THE PROS AND CONS OF CLONING (AND OTHER REPRODUCTION TECHNOLOGY TECHNIQUES)
This article looks at several areas of what is known as 'reproduction technology' and how it could affect cat breeders and cat owners. These pros and cons will also apply to other pets. Reproduction technology includes cloning, artificial insemination, egg donation, embryo transfer and IVF. It also includes information on genetic modification, a further technique which could be applied during cloning. I have basic knowledge and understanding, but do not claim to be an expert in these fields. I have written this so that an owner or breeder with little or no prior knowledge can understand it. I have included general interest comments about some of the wider issues of cloning in species other than cats. (This is still a working draft and will be updated and refined)
Cloningis the creation of a genetically identical cat from a cell taken from a host (the genetic parent) and grown into a kitten inside a surrogate mother.
Artificial insemination using stored sperm is the gathering of sperm from an unneutered cat and the impregnation of a female cat using that sperm.
Egg donation is the harvesting of a freshly ovulated, unfertilised egg from one female; the egg is fertilised in vitro (i.e. "test tube fertilisation") and implanted into a surrogate who cannot ovulate
Embryo transfer is the implantation of an embryo or fertilised egg (one which has already begun to divide ad grow) into a surrogate mother. The embryo (or the egg and the sperm used to make it) might have been kept stored in liquid nitrogen for a period of time before being implanted into the surrogate mother.
IVF is in vitro fertilisation, often known as 'test tube fertilisation'.
Ova means 'egg cells'.
A FEW BASICS
The following is greatly simplified and is based on information in Matt Ridley's excellent book "Genome" and has been adapted for cat owners. However, you can skip this section if you prefer. It is provided to give an understanding of cell division and why there are still problems with cloning technology.
The cells in a cat's body continually divide and replace themselves. Cells multiply during growth to make more tissue and skeleton as the kitten grows and matures. When the cat is full grown, cells continue to reproduce themselves. Cells wear out and die and are replaced by newer ones copied from the old cell. As the cat gets older, the cells are less efficient at making exact copies of themselves and mistakes creep in. It's like monks copying books by hand - sometimes a spelling error creeps in; the monk who copies the new manuscript also copies the spelling error and maybe adds another error. As the mistakes accumulate, the cat (the host body that the cells live in) shows signs of ageing.
How does the cell know how many time it has divided? The genes (lengths of DNA) are stored as strings called chromosomes in the cell nucleus. DNA is like an alphabet; the gene is like a word and the chromosome is like a sentence. At the ends of each chromosomes is a telomere - these are like strings of full stops. In young kittens, the telomeres are relatively long and there are lots of full stops in each telomere. Each time the cell divides, the telomere gets shorter as a full stop is lost off of the end. This is part of the ageing process and seems to be why animals grow old. The telomeres are also like a clock, telling the chromosome in the cell how old the cat is.
In effect, a cell taken from a cat knows how old it is. For instance, a kitten might be cloned from a cell from a ten year old cat. Although the kitten is newborn, all of its cells are saying that they are ten years old. Most likely the clone will age faster than a kitten produced in the normal way. It seems like premature ageing but it isn't, those cells are already older than the host body and older cells don't copy themselves as efficiently. Scientists are already seeing this in Dolly the sheep - when Dolly was three years old, all her cells were six years old because they had already aged three years in her 'mother' before being passed on to the clone (I forget how old Dolly's 'mother' actually was, but hopefully you get the idea).
Dolly the cloned sheep died aged six in February 2003 of a progressive lung disease. Sheep can live to 11 or 12 years old and the disease is normally associated with older sheep (especially those housed indoors). This suggests that clones made from the cell of an adult animal are inheriting "pre-aged" cells (an analogy is old wine poured into a new bottle continues to be old wine, it does not become young wine again; only the container is new).
At present, the only way to overcome the problem of premature ageing in clones is to clone very young animals or to take a fertilised egg which has begun to divide and to split it into several parts (the same way nature creates identical twins and triplets).
Although premature ageing is the normal rule, there have been instances in cattle cloning where the telomeres have not only rejuvenated, but are actually longer than normal. The clones are potentially longer-lived than the donors. At present, no-one is ceertain why these clones (calves) are the exception to the rule.
CHRONOLOGICAL AGE AND BIOLOGICAL AGE
Chronological age(calendar age) is the time elapsed from date of birth to present day. In normally conceived animals, the chronological age is what we refer to simply as "age" - the number of years we have existed, the number of birthdays we have celebrated.
THE FIRST CLONED CAT
On 14th February 2002,cloning scientists in Texas publicly announced the world's first "Copy Cat" - a cloned kitten named Cc. Cc (nicknamed "Copycat" or "Identicat" by the media) was made from a cell taken from an adult tortoiseshell female. The nucleus of this cell was inserted into an egg in a technique called "nuclear transfer" - the same technique used to make Dolly the sheep. It is believed to be the first time a domestic cat has been cloned; attempts to clone a dog had failed.
Mark Westhusin and his colleagues from the College of Veterinary Medicine at Texas A&M University fused a cell from one of the adult cat's ovaries with an egg from which the nucleus had been removed. Genetic material from the adult cell was transferred into the egg. This grew into an embryo and was implanted in a surrogate mother. Out of 188 attempts to create embryos, 87 cloned embryos were made and transferred into 8 surrogate mothers. Only two resulted in pregnancies and only one pregnancy was successful.
Cc was born by Caesarean section on December 22nd 2001. She was reported to be vigorous at birth and appeared to be completely normal. Despite being a clone, Cc's coat has a different pattern from that of the donor cat because the pattern of pigmentation in multi-coloured animals is not solely caused by the genes, but also by the way the cat develops i.e. what genes are switched on or off in each individual skin cell (though the cells may be identical, some have "black" switched on while others have "orange" switched on).
Although the reports describe Copycat as a tortoiseshell, the photos issued to the media very clearly show a tabby-and-white, not a tortoiseshell (black-and-orange) which suggests scientists (or more like reporters) may be improving the cloning process, but they have a great deal to learn about cats in general! The donor is a tabby-tortie-and-white called Rainbow. Cc's disposition is also very different from that of her genetic mother. Temperament is controlled partly by genes and partly by environment, both inside the womb and during a cat's lifetime.
Though this seems a great step forwards, the failure rate is still extremely high - only 1 out of 87 attempts resulted in a clone - and the kitten was not born naturally. There will also be other DNA present because only the nucleus was transferred to the egg - other parts of the cell (the mitochondria) will not have come from the clone donor cell but from the egg cell.
Cc came from a cumulus cell - a type of ovarian cell which surrounds developing eggs and which is, therefore, found only in female animals. Other implanted embryos came from skin cells. Cc's birth may mean scientists have found a reliable method for producing female cat clones. In mice, male clones have been created from Sertoli cells which come from the testes; this could also work in cats.
On the day Cc was born, 6,000 unwanted pet cats and kittens were destroyed in the USA.
LIMITATIONS OF CLONING 1 - GENETIC DEFECTS AND GENDER
A clone will be identical to the genetic parent (tissue donor). It will be the same sex and it will have the same genetic defects or mutations which were present in the tissue donor. Genetic research is advancing so that one day genetic defects might be weeded out of individual cells and healthy genes inserted instead (e.g. using a virus to carry healthy genes into the cell) but at present the clone will be as healthy or as unhealthy as the tissue donor.
Cloning relies on the fact that all cells contain the instructions for making a whole body. For example, in its DNA a skin cell contains the instructions for making an eye. In the normal run of things, the skin cell doesn't make eyes so if something goes wrong with its copy of the "make eye" genes (e.g. damage from sunlight or chemicals) it is not disastrous, because the skin cell is making skin cells (which will inherit the damaged "make eye" genes) and not eyes. However, if that skin cell is used to make a clone, the clone will inherit damaged "make eye" genes. Something will go wrong with the formation of eyes in the embryo.
In the normal run of things, an embryo inherits a set of genes from each parent, giving it a "back-up" copy if any genes are damaged or defective. It is very bad luck if both copies of a particular gene are defective. In a clone, there are no back-up copies of genes. Localised damage in the donor cell are passed on to the clone. The older the donor, the more likely there is to be damage. Though the damage might be invisible in the donor cell, it could be disastrous in the clone. This may be why so many attempts at cloning produce defective embryos - they are being made from cells with damaged DNA. The damage will show up when the cell tries to run certain instructions which it would not normally run when doing its normal function (e.g. being skin).
The clone will be the same as the original was before any accident, illness or surgery. If the original was neutered, the clone will be unneutered because "acquired traits" (things done to the animal during its life) cannot be inherited. The only exceptions to this is cell mutations caused by cell poisons or radiation; clones made from radiation-damaged cells will be equally damaged because the DNA itself has been damaged.
When the highly successful American racehorse, Cigar, was put to stud, he proved to be infertile. There was talk of cloning Cigar. However, if the original Cigar is infertile because of a genetic defect, his clone will also be infertile. If the original Cigar is infertile because of an illness or injury, the clone should be fertile.
A clone will be the same gender as the tissue donor. At present there is no way to change a clone's gender. The chromosomes which determine gender are the sex chromosomes. Females have 2 'X' chromosomes (XX) and males have one X and one Y (XY). A few individuals have multiple sex chromosomes or only one sex chromosome, but these are out of the scope of this article.
Scientists have considered creating female clones from male cells by removing the Y chromosome and somehow duplicating the X chromosome. This is fine in theory but may not work in practice because some genes on the sex chromosomes HAVE to be inherited from the father if the offspring is to be normal. These issues are complex and are discussed in detail in Matt Ridley's "Genome".
In humans there are all sorts of conditions which arise if genes are inherited from 'the wrong parent' . This occasionally happens in nature if 2 ova (egg cells, these always contain an X chromosome) fuse to create an XX embryo without any genes from a male parent. Also, there isn't yet a way of turning an X chromosome into a Y chromosome to get a male clone from a female tissue donor.
LIMITATIONS OF CLONING 2 - COLOUR AND PATTERN
There's bad news for owners of tortie and calico cats.
DNA tests have confirmed that Cc is a clone of her genetic mother. Yet her coat colour and pattern is different from that of her mother because the pattern of pigmentation in multicoloured animals is the result of genetic factors combined with developmental factors within the womb. This means bad news for owners who want an exact replica of a tortoiseshell or calico cat.
Cc’s genetic donor is a calico (the American term for tortoiseshell and white) domestic shorthair. Cc is a tabby-and-white domestic shorthair. Why isn't Cc a calico like her genetic mother? The answer is due to ‘X-linked Inactivation'.
Tortoiseshell and calico cats are almost always female, which means they have two X chromosomes. One of those X chromosomes contains the gene for orange coat colour. The other X chromosome contains the gene for black coat colour. As the embryo develops, a process called ‘X-linked inactivation’ occurs in its tissues. One or the other X-chromosome in every cell in a tortoiseshell or calico cat embryo is randomly inactivated.
This shows up in hair and skin cells as patches of different colours. If the X-chromosome containing the gene for orange coat colour is inactivated, that cell goes on to produce black coat colour. If the X-chromosome containing the gene for black coat colour is inactivated, the cell produces the orange coat colour. If the deactivation happens early on, it produces relatively large and well-defined patches of colour. If it happens later during development, it produces a brindled effect.
The white patches and the tabby pattern are both caused by different genes entirely.
Regardless of which cell was used to produce Cc, because that cell is already an adult cells, one or other of its X chromosomes would have been inactivated while the donor cat was an embryo. Cc had an equal chance of being orange-and-white (or orange-tabby-and-white) or black-and-white (or tabby-and-white), but would never be calico. Unless a way can be found to undo X-linked inactivation at the embryo stage, owners wishing to clone a tortoiseshell cat will have to settle for a cat of a different colour entirely. If the X-linked inactivation can be reset, the inactivation appears to be a random process so the clone will have the right colours, but not in the same places as the donor cat.
HOW IS CLONING DONE?
Genetic copying involves transferring a cell nucleus from the donor cell (the one to be copied) into a recipient cell (typically an unfertilised egg token from an animal soon after ovulation). Cc (Copycat) was made from an ovarian cell, but the idea of cloning is that any body could be used.
The vet takes a small skin sample (much like taking a skin punch biopsy) from the abdomen of a living cat or one which has just died. This requires only local anaesthesia and a small shaved area in a living cat. The punched out area is closed with a couple stitches. This tissue sample is sent (or taken by courier) to a biotechnology lab in a special mailing package to preserve it.
At the laboratory, the cells are grown, harvested and frozen in liquid nitrogen. When needed, the tissue cells are put in petri dishes and provided with nutrients so that they divide and multiply. They may need chemical treatment to stimulate cell division. Within days, new skin cells appear and within one month, the new cell count totals in the millions. This is much like growing skin for skin grafts and this method could be used to grow new tissues for transplant.
Nuclei can now be extracted from these cultured cells of the tissue donor (the biological "parent"). The extracted nuclei are inserted into recently ovulated egg cells (ova), which have had their original nucleus removed in a process called nuclear transfer. The egg cell donor may have been chemically stimulated into producing these eggs. Since cats are induced ovulators (ovulation is triggered by the act of mating) they could be made to ovulate by physical rather than chemical means. The egg cells which now contain transplanted nuclei from the tissue culture are chemically treated to stimulate the normal division of a fertilised egg cell into an embryo. This is implanted in the womb of a surrogate mother cat. If all of the preceding stages have been successful, the embryo continues to develop. If the foetus is carried to term, the surrogate mother will give birth to offspring that will be genetic matches of the original cat.
At present, the success rate is still very low. In rabbit cloning experiments at the National Institute for Agricultural Research in Paris, researchers discovered that one of the keys to success is in the timing of various steps, such as how long to expose the early embryos to certain chemicals and when to implant them in the host mother's womb. Even so, the success rate was 4 live rabbit kits from 371 implanted cloned embryos.
Scientists have shown that clones can be created from a donor which has already died. In April 2002 at the University of Georgia, a calf was produced from cells taken from a kidney cell from a standard slaughterhouse side of beef, 48 hours after slaughter. This demonstrated the viability of cells for 48 hours after the death of the donor animal.
During 2004, a method called chromatin transfer was pioneered. Only the donor chromosomes are transferred into the host egg. This is in the early stages, but seems more efficient and reliable than nuclear transfer and less prone to abnormalities.
WHEN WILL CAT CLONING BECOME AVAILABLE?
Many of the individual techniques already exist. The technology for storing tissue has long been available. It similar to that which is used for storing sperm, eggs or embryos for human fertility treatment. Stored sperm has long been used for artificial insemination of cattle so that the farmer doesn't have to keep a bull (most bulls are aggressive and difficult to handle). Skin can be grown in the laboratory allowing a patient's own skin to be grafted onto him.
Scientists have already split fertilised eggs into individual cells to give rise to multiple foetuses. They have merged pairs of fertilised eggs into a single egg to give rise to a "mosaic" offspring (one which looks perfectly normal but which a mixture of genetically different cells in its body). Most of these things have been done with mice, however scientists have merged the embryos of a sheep and a goat to create a hybrid called a "geep". Cloning a new individual from a cell other than an egg cell has always been a challenge. For many years it was possible to clone simpler animals e.g frogs, but not more complex ones.
Cloning hit global headlines in 1997 after Scottish scientists at the Britain's Roslin Institute, UK, successfully cloned Dolly from an adult sheep cell. Since then, researchers have replicated mice and other creatures including an endangered Gaur (a cow bore the Gaur calf; the calf died of dysentery but this was not related to the fact that it was a clone). Sheep, goats, cows and pigs have been cloned. In the most efficient and successful cloning experiment to date, dozens of mice over six generations were cloned from a single mouse. This has led to several avenues of research such as the cloning of a mammoth from tissue frozen in Siberia or the cloning of dinosaurs (such as depicted in "Jurassic Park"). There is hope for resurrecting recently extinct species such as the quagga (a type of zebra), thylacine (Tasmanian wolf) or dodo using DNA from taxidermised or preserved specimens. "As dead as a dodo" might no longer be true.
Right now, mammoths and dinosaurs are a long way into the future as well as being a long way in the past. However, scientists at commercial cloning companies are feverishly manipulating genes in hopes of becoming the first to clone a domestic cat. But to do this, there are major problem areas to be overcome,
Nearly all of the animal cloning experiments to date have suffered high rates of foetal and neonatal mortality in the resulting offspring. All sorts of things go wrong, according to George Seidel, a cloning researcher at Colorado State University. For example cloned cattle and sheep are often born dangerously large. "Normally you might expect a 100-pound birth-weight in a calf, but with a clone, you might get 160 pounds," said Seidel (i.e. between one and a half to twice the size and weight). Genes which control the "switching on" and "switching off" of growth may not work correctly in clones.
Oversized foetuses don’t have room to wriggle around in the uterus and can be born with limb deformities. They may have to be delivered by caesarian section or may die in utero. Seidel points out that ‘Sometimes the kidneys aren’t right, they’re just plain put together wrong - or the heart is, or the lungs, or the immune system.’ Currently, nobody really knows why, but the abnormality rate is around 30 per cent in cloned animals. The normal rate of congenital defects (i.e. non-cloned offspring) is probably less than 5 per cent, which is possibly why most species use sexual reproduction - it has a form of error correction mechanism.
Among the defects found in cloned animals are developmental abnormalities where a vital organ is only partially formed or is formed largely out of undifferentiated cells. The organ cannot function once the offspring is born; it does not contain the appropriate cells. A normal fertilized egg contains instructions to tell tissues when to make specialized cells and also when stop developing. In cloned animals this can go wrong - blood vessels may be four or five times too large and the heart cannot cope with pumping blood around these enormous vessels; the liver or lungs might be little more than tumours of non-specialized cells which cannot act as liver cells. It appears that genes which were active in a fertilized egg and then switched off later in life are not "switched on again" if a clone is attempted using a cell from an adult animal. This may be why there has been greater success with creating clones from embryos - the crucial "switching on" and "switching off" genes are still active in embryos.
Some abnormal embryos may be due to damage caused by handling the cell during nuclear transfer or when handling the early embryo; conventional IVF in cattle can also result in oversized offspring. Embryos are usually nurtured to the blastocyst stage (about 120 cells) in the laboratory before being implanted into a surrogate mother. The chemical soup used to nurture early embryos may not be quite right, resulting in abnormal development. The donor cell may contain mutations or damaged DNA; this is invisible when the cell is a tissue cell, but it causes deformities when the cell is used to build a whole organism.
In 2002, American scientists identified a single gene which could explain why most attempts to clone mammals end in failure. It is believed that cloning failures happen because genes from a tissue cell are not reprogrammed into being able to produce a new individual. For cloning to succeed, tissue cell nuclei (which would simply produce more tissue cells) must be reprogrammed in to behaving as embryo cell nuclei (able to produce a whole individual). It appears that gene-reprogramming often fails to occur adequately during cloning attempts. As a result, only about 1% of manipulated eggs lead to a live animal. Of those clones which are born live, many have abnormalities.
Scientists examined cloned cells for a gene which only appears if donor nuclei can reprogramme themselves to develop as embryos rather than as tissue cells. Only a third of donor nuclei showed the gene at all. Many of those did not show it at the right levels. Those cells either do not develop or do not produce a normal embryo. Experiments with mouse embryos, suggest that one particular gene (the Oct4 gene) crucial for early development is often not reprogrammed properly during cloning. Its level of activity is inappropriate for creating a new individual and the cloning attempt fails. With a few famous exceptions (Dolly the sheep and Cc the cat) surviving clones are often short-lived and have abnormal tissues. Though this single gene does not explain every failure, it could account for as many as 90% of failures.
The more recent method of chromatin transfer is claimed to be less prone to producing abnormal foetuses and more reliable at producing clones with correctly formed and correctly functioning internal organs. However only time will tell if it is truly safe.
A controlled study of the lifespan of clones produced through nuclear transfer, almost all of a batch of cloned mice produced by the National Institute of Infectious Diseases in Tokyo died earlier than their naturally bred cousins. The experiment suggests that some effects of cloning aren't apparent in early life. Twelve male clones were compared with control groups of 7 naturally conceived males and 6 "test-tube" conceived mice. Just over 2 years later, 10 of the cloned mice had died compared to 3 of the non-cloned mice. Contributory causes of death included pneumonia, liver disease/cancer and poor immune systems. In an experiment with cloned mice at the University of Hawaii, 1 in 3 clones born looking normal became massively overweight within a few weeks.
Cc the cloned kitten may have given pet owners false hopes for re-creating deceased pets in the near future. Cloning will never be an efficient form of reproduction until scientists find a way to reprogram genes vital for building a healthy embryo. Chromatin transfer may be a partial solution.
Whether the cat fancy is ready for it or not, experts believe that cat cloning isn't far away. The first feline clone might be seen as early as 2001 according to Richard Denniston, president of Lazaron Biotechnologies and a member of the animal science faculty at Louisiana State University, Baton Rouge, USA. Already, experts and researchers from the fields of cell banking, cloning, tissue culture and feline reproduction are working on cat clones.
WILL PET OWNERS BENEFIT?
The company that produced Cc (nicknamed Copycat or Identicat by the media) could charge wealthy pet owners thousands of pounds to replicate animals which die. It could also be used to replace socially valuable animals such as outstanding guide dogs, search and rescue dogs or transgenic animals such as pigs bred for organ donation to humans. It could be used to increase breeding stocks of endangered wild animals, but it will not widen the gene pool. It is claimed that commercial pet cloning will be the first breakthrough in cloning technology to directly benefit the public.
In Britain, the Animal Procedures Committee, which advises the home office, says cloning for such frivolous purposes should be banned. At present, cloning a single cat would cost £7000, but this could fall to £700. Dogs are more expensive because a bitch (surrogate mother) comes on heat less often than a queen (unspayed cat) - a cloned dog could cost £70,000, falling to £5,000. In the USA, there is currently no legislation against animal cloning. Officials in California have banned genetically modified, fluorescent (but sterile) zebra fish on ethical grounds; there may be restrictions on cloning on similar grounds. Lou Hawthorne, CEO of the Californian animal cloning company "Genetic Savings & Clone" (which worked with Texas A&M University in producing Cc) believes regulation would drive out charlatans, but would not affect companies such as his own. His company hopes to clone thousands of pets annually in five years' time, when the cost should be down from $50,000 to $10,000 for a cat clone ($20,000 for a dog clone).
When Cc was born in 2002, it was believed that the first feline clones would be laboratory animals for scientific research. Several species have been successfully cloned around the world, including mules and horses. In 2004, Genetic Savings & Clone launched a cloning service for pet owners. Even before that date, some American cat owners had tissue samples from their cats stored ready for commercial cloning. The banking of tissue samples for cloning cost approximately $700 - $1000 plus $100 - $150 per year to keep the sample in storage (maintenance costs). Cells for banking are harvested through a tissue biopsy performed by a vet. Coin-sized samples are taken from the pet's stomach and from inside its mouth.
When CCc was born, no-one knew how much commercial cloning would cost, though the price would fall once the technology was perfected and more reliable. At present cloning is costly since out of 200 attempts, only one or two clones might be born. Many eggs containing transplanted nuclei simply fail to develop or develop in an abnormal way and die in utero.
If the process is perfected, cloning could lead to mass-production of genetically identical animals destined for far less happy lives in experimental laboratories. Cats are used as experimental subjects in a number of laboratory and medical experiments. Reducing the genetic variation between cats removes many unknowns from experimental procedures e.g. their reaction to drugs, disease or surgical procedures. Cloning potentially gives researchers the ability to create large numbers of genetically identical cats. It would allow the mass-production of kittens with genetic defects such as missing enzymes or abnormal organs; a single genetically defective kitten (which would not reach reproductive age) born through random mutation could give rise to a multitude of defective, short-lived kittens destined purely for research.
Such cats would be born and raised in a pathogen-free environment, mass-produced to order and destroyed during or after experimentation. This raises concerns not only about the clones' welfare (mass-production already reduces experimental animals to nothing more than "living tools"), but also about the welfare of the surrogate mothers who would be kept in sterile surroundings and regularly anaesthetised to allow embryo implantation - and possibly for routine caesarian births.
At first, cloning pets will be something only wealthy owners can afford. In 2004, Genetic Savings & Clone reported that five customers were having cats cloned at a cost of $50,000 each. Work was due to start in May; if successful, the first kittens would be born in November. The company had already begun to clone three other cats for staff members, including a clone of Hawthorne's own Bengal cat. The clones would be presented to the American Veterinary Medical Association conference next year. The company gives an important "buyer beware" warning: the clones will be unique, newborn animals, not the full-grown exact replicas depicted in movies such as "The Sixth Day". Cloning is resurrection of genetic content, but is not resurrection of an individual animal.
In August 2004, Genetic Savings and Clone announced 2 further cloned kittens, by hen 8 weeks old: Tabouli and Baba Ganoush. They are clones from a one year old female Bengal, were cloned by chromatin transfer and belong to GSC's CEO. The kittens are described as strong, healthy and identical to their genetic (donor) mother. This is unlike CC who, although healthy, had different colouring and a different disposition to the donor cat. DNA tests will confirm that the kittens are identical to the donor cat, Tahini and they will be exhibited at the Cat Fanciers Association Show in New York in October 2004. Two more cloned kittens are due, being clones from GSC employees' cats. Five cat owners have already applied to have their pet cloned at a cost of $50,000 each.
According to GSC, chromatin transfer is safer and more efficient and reliable than previous nuclear transfer methods of cloning. Chromatin transfer is apparently responsible for the kittens' likeness to their mother. It is a more advanced technology than that used to produce CC. However, critics of cloning point out that the kittens could have hidden defects, including premature ageing. GSC has said that clients will get their money back or a another clone for free if cloned pets had any genetic defects.
Chromatin transfer is more successful than nuclear transfer because all of the genes are expressed at the right levels and correctly form the right cell types e.g. lung tissue forms correctly and behaves like lung tissue should. This means the clones are healthier. It also produces the correct coat colouration, size, conformation and facial features. One reason for the kittens' strong resemblance to the donor is that Bengal cats (like other pedigree breeds) have already been selectively bred for consistent pattern and conformation. The patterns of tortoiseshell, tortie-and-white and bicolour cats are determined during embryo development, making it impossible to create identical clones.
Curt Youngs of the Animal Science Department of Iowa State University fears that some pet owners will still not understand that clones are not reincarnations of the animal that donated the cells. David Magnus, of the Center for Biomedical Ethics at Stanford University, said that people could be spending huge sums of money in the mistaken belief their pet would be immortalised or to get an identical copy. According to Hawthorne, anyone who is not happy will get a full refund and the animal will be put up for adoption.
The Humane Society of the United States has also taken issue with pet cloning. In addition to the concerns over the welfare of surrogate mothers, the USA already has a chronic feline overpopulation problem. Shelters kill around four million healthy, but unwanted, animals every year. The HSUS feels that owners will have animals cloned because the owners are unable to deal with bereavement. There is the possibility of unwanted clones - either because the cloning process produced multiple individuals, or because of owner disappointment. Some owners might also request "enhancements" to the clones e.g. genetic modification to create a hypoallergenic copy.
Although CC is currently a healthy two year old, Dolly the sheep showed signs of premature ageing. Owners and adopters of clones could be in for a nasty surprise if their expensive clones turn out to be shorter-lived than conventionally conceived animals.
Doggy Note: The Missyplicity project, originally run from Texas A&M University and now moved to Genetic Savings & Clone, was founded in 1997. The project aims to clone an elderly mongrel called Missy whose traits were considered worthy of perpetuating (Missy had been spayed). It originally aimed to create dog clones by the year 2000, but cloning canines is problematical due to their reproductive cycle. There is a shortage of donor eggs because the eggs of a bitch mature just before she goes into heat; this only happens every few months and is unpredictable times (but might be overcome with hormone treatment). When a cloned canine embryo is made, a suitable surrogate, also in heat, is needed to implant the embryo into; the unpredictable reproductive cycle could mean freezing any cloned embryos for implantation later (and risking damage). Missy died in 2002, but her banked tissue continues to be used.
WHY CLONE PETS?
The question is not "when will a cat be cloned?" but "why do we want to clone a cat?" There are ethical and emotional issues surrounding cloning. These issues affect cat owners, vets, animal shelters and scientists. There is also the bio-ethical argument of meddling with nature. Many people believe that science is already meddling too much with nature and that the human race is trying to "play God". Many believe that we are a short step away from designer babies - and designer pets.
Despite the portrayal of instant clones in the movie "The Sixth Day", it is not possible to grow blanks which can be impregnated with an individual's DNA. It is also not possible to transfer memories from an individual (the cell donor) to a fast-grown clone which then becomes a near-perfect duplicate of the original.
Companies in the US are already storing tissue samples from pets. Genetic Savings & Clone (GSC) of Texas, owns the commercial rights to the cat-cloning technique and plans to offer cloning services to a few clients in the near future. Genetic Savings and Clone will apparently not accept customers who have unrealistic beliefs that cloning can recreate their pet. Such unrealistic hopes have been made worse due to "The Sixth Day".
Charles Long of Genetics Savings and Clone said "We try to make it clear to them we can't resurrect their animal. The best we can do is make a genetic duplicate." Even this is misleading because the clone contains mitochondrial DNA from the host egg; this mitochondrial DNA also has an effect on the end result.
Herb Neiburg, Director of Behavioural Medicine at Four Winds Hospital near New York, provides pet bereavement counselling and he feels that these warnings may not be strong enough. He has seen people abuse or abandon normal replacement pets which don't live up to an owner's expectations. Those people are likely to have even higher expectations of a clone and should receive professional counselling to determine whether cloning their previous pet is really the answer to their grief.
However, some owners will do almost anything to get a beloved cat back, even after the pet has died. Some owners want their cat's likeness and personality restored in a clone. They argue that a similar looking cat of the same breed is no substitute. Cloning is of special interest to owners of mixed breed cats which have been neutered. Owners have very strong emotional bonds to their individual cats and the emotions of grief and loss can be so overpowering that the only comforting thought is that a deceased pet can be somehow brought back to life. However, the cat is not being resurrected except in a genetic (breeding stock) sense since the clone is a different individual. It may be physically identical but it is not the same animal in personality.
However, most cat owners will adopt another cat when the pain of grief becomes bearable or because they cannot imagine a life without a feline companion. Some get a cat which is similar in looks and temperament, others want a cat which does not resemble the deceased pet. A few never get another cat, but rarely solely because the previous cat was irreplaceable. The cloning of the deceased pet might deny a home to the cats that would otherwise have adopted. For this reason, many cat rescuers oppose cloning as being based in selfishness. With so many cats destroyed in shelters every day, why add to the feline population through cloning? In the USA, 5 to 7 million unwanted cats and dogs are destroyed at animal shelters each year. Although the clone will be wanted, it potentially denies another cat a home. In addition, several egg cells may be implanted into a surrogate mother (in case some do not develop) so what happens if the surrogate mother gives birth to two, three or even more clones? Will the owner of the biological parent want all of the kittens?
The clone will simply not be the same animal as the original. A cat's personality is shaped by a combination of nature (genetics) and nurture (environment). The clone may be physically identical and inherit a similar temperament (e.g. the laid back temperament of Ragdolls), but it will not have an identical personality. The owner will also be 10-15 years older and will have changed - personality traits which were endearing when the owner was single might be a nuisance in a busy household. The clone itself would be forever living in the shadow of the original without getting a chance to be itself and maybe failing to live up to the owner's expectations.
In Feb 2001 the results of the Human Genome project showed that humans have far fewer genes than previously thought - a mere 30,000 - 40,000 rather than 150,000. There simply aren't enough genes to have one each for all the characteristics that have been associated with them e.g. personality traits. This will be equally true for other animals, such as cats, and it indicates that nurture is a far more important force than previously believed. Genes provide the potential for certain traits, but environment determines whether or not those traits will be expressed. Using a simple analogy: a person with the aptitude for being a gifted pianist will never achieve this if they never see or use a piano. The vital role of nurture is an especially important consideration where an owner wants to "bring back" a cat they adopted as an adult without knowing much about its formative years. The different nurture received by the clone means that the clone will grow up to be a far different individual to the original pet.
Very few people value their cat purely for its appearance. They value its personality, something which has developed over the cat's lifetime. The clone will not inherit the original cat's memories and since the original cat's cute antics were learned, not inherited, the clone will act in a different way as it lays down its own memories. Personality and behaviour are not the product of a few genes, they are also the product of a lifetime's experience which cannot be inherited. The owner could be seriously disappointed that the clone does not match their memories of a previous pet.
The physical resemblance to the deceased cat combined with this disappointment could be so great that the owner begins to resent the clone for not being identical in personality to the previous cat. I have seen this when an owner adopts a cat which is "the spitting image of my old one" . Resented for being itself, the cat is all too often returned to the shelter or breeder, or worse it is neglected or abandoned. A resented clone, or multiple clones, could simply add to the feline overpopulation problem.
GENETICALLY MODIFIED CLONES
In 2001, it was announced that hypoallergenic cats could be produced. Transgenic Pets of Syracuse, New York announced plans to create GM cats whose skin doesn't secrete the Fel d 1 protein that causes most allergies. David Avner Transgenic Pets has a patent pending on the idea of hypoallergenic GM pets and has a contract with a cloning expert at the University of Connecticut, to produce the cats. If all goes to plan, GM cats could be produced as early as 2004 and cost $1000 each. All would be spayed or neutered prior to sale.
The gene which produces the Fel d 1 protein may play a minor role in protecting the cat from bacteria. Scientists don't know how minor or major its role is - they plan to just remove it or knock it out and see what happens. Skin cells altered in this way can then be used to create clones. Both male and female clones would be required and if those clones prove healthy, they can be bred in the normal way and their offspring sold. However, those clones could carry subtle defects which manifest later in life and which have already been passed on to their descendants.
People for the Ethical Treatment of Animals (PETA) in Virginia are unhappy with the "try and see" approach to knocking out a gene which may play a role in the cat's defence against bacteria. The note that disabling it could have adverse effects which lead to suffering. The anaesthesia of host mothers for implantation of embryos, often repeatedly, also has potential to cause suffering.
GM also has the potential to create pets which are longer-lived, have breed-specific genetic defects corrected or are disease-resistant. Advocates of biotechnology and GM techniques claim this is merely speeding up the selective breeding processes which have been used for centuries. It could also produce pets which don't moult (shed), which are more docile and which have hitherto unseen coat patterns and colours - for example cats with the coat pattern of a tiger or the mane of a lion. If this seems far-fetched, consider the fluorescent green rabbit which has already been produced and imagine a calico cat with patches of ginger, black and fluorescent green.
For pet owners seeking replacements for a pet which died of an inherited condition, GM could potentially be used to eliminate a genetic factor which caused the condition and produce a disease-free clone. All of this is still years away.
As with hypo-allergenic cats, the first step would be manipulate cells which would be grown into clones. Those clones would be the foundation of the new improved breed.
A potential downside of GM is that GM and transgenic pets could interbreed with closely related wild species and pass on their modified genes. Some species are already endangered due to interbreeding with domestic pets e.g. the Scottish Wildcat and the wolf. Without knowing the long term effect of genetic modification in the domestic animals, the long-term effects on wild species would be hard to predict. The modified genes might simply be a tiny drop in a huge genetic ocean and might be bred out. Or they might lurk there like a genetic time-bomb in a small gene pool among animals already badly inbred. The effect of those genes might be insignificant compared to existing interbreeding with domestic stock or it might be the final nail in the coffin for the wild species.
Although would-be cloning companies (whether intending straightforward cloning or GM cloning) claim that all the animals they create will be adopted as pets, this will be at the expense of millions of naturally conceived animals. Already 6,000 unwanted cats are destroyed daily in the USA and this number could increase if owners prefer to acquire cloned or GM cats.
LOSS OF DIVERSITY AND CLONING FOR CURIOSITY
Cloned animals have the same genetic make-up as the tissue donor. You can breed the clones together and get different-looking offspring, but there is only a limited variety of genes which can be passed around. Using clones in a breeding program means losing genetic diversity while increasing the incidence (concentration) of other genes in the breeding population. Using clones of stud cats is likely increase the incidence of inbreeding.
The problem of inbreeding is covered in my article "The Pros and Cons of Inbreeding". Because the clones are genetically identical, genetic diversity will being lost. This could lead to lower disease resistance especially to a new disease, greater incidence of harmful defects (as more of the breeding population carry the genes for those defects) and reduced fertility when breeding in the time-honoured male-impregnates-female way. It leads to what is known as a genetic bottleneck and a loss of hybrid vigour.
People for the Ethical Treatment of Animals (PETA) are opposed to the cloning of endangered species, fearing that the cloned animals will be bred for zoos and that nothing will be done about preserving the species in the wild by preserving its wild habitat. Take it one step further and there is the problem of resurrecting an animal e.g. a mammoth whose habitat has already vanished. This is cloning for curiosity's sake. What does this have to do with cats? What if a mutated cat is born which is so deformed it cannot breed, but which breeders think is 'kinda cute'? Create a few clones and use surrogate mothers of course! Curiosity might clone the cat.
There are benefits in cloning endangered species or cloning livestock for selective breeding e.g. cloning from animals which don't carry harmful genetic traits, cloning those which are genetically resistant to certain diseases or rapidly increasing the breeding population of an endangered species. Cloning technology could produce cattle herds free of the prion protein gene which causes BSE (mad cow disease) and which appears to be transmissible to humans, causing New Variant CJD (vCJD).
Surrogate mothers don't even have to be the same species as the clone, as long as they are from a closely related species (and even that barrier is being overcome by the manipulation of the immune system). In the field of embryo transplantation, a domestic cat could give birth to kittens from an endangered wild species of cat. At the Audubon Institute’s Centre for Research of Endangered Species there is a "frozen zoo" of cells from exotic and endangered animals. In 2000, researchers implanted caracal embryos in a domestic cat. She gave birth to twin test-tube caracals. A domestic cow carried a cloned Gaur calf.
Looking for a moment at the wider issue of cloning, it is a concern to those who are opposed to other forms of animal exploitation. Laboratory animals (including cats and dogs) could be cloned for experimentation, especially if they come from a genetically engineered individual. A goat could be genetically engineered to produce substances in its milk; a whole herd of goats can be cloned from that individual so that the yield is increased. It's not so far-fetched - antithrombin-3, a protein in goat’s milk can be a valuable source in heart medications. Other specific animal proteins could be mass produced through cloning to provide necessary ingredients for medications to help people with diseases such as cystic fibrosis, diabetes or degenerative diseases. Transgenic animals (animals containing implanted genes from another species) could be cloned, perhaps because their organs can be transplanted into humans.
ARTIFICIAL INSEMINATION, IVF AND EMBRYO TRANSFER
Cloning may be the most advanced and ambitious aspect of reproductive technology, but it is not the only technique. Other techniques have already been refined for use in livestock breeding and in human fertility treatments.
Sperm can be obtained from an anaesthetised stud cat by electrical stimulation of the prostate gland. Anaesthetic is required because the stud cat will almost certainly resent this sort of handling. All anaesthetics carry a small amount of risk. An alternative would be to collect the semen in a sort of 'condom' placed inside the queen's vagina, but to the best of my knowledge this has not been tested.
The collected sperm is diluted in a suspension fluid so that the sample can be divided up into a number of portions. These can be frozen or used immediately to inseminate a number of cats. This has the advantage of allowing a cat to impregnate a greater number of queens, but the disadvantage of increased inbreeding. In the queen, ovulation is triggered by the stud's penetration and withdrawal; this would have to be simulated if artificial insemination was to be used.
In addition there is a chance that sperm samples get mixed up so that a kitten with 'Stud Cat X' on its pedigree was in fact fathered by 'Stud Cat Y'. In a breeding program this could cause havoc as the 'wrong genes' get passed on and inadvertent and undesirable cross-breeding might occur. Artificial insemination is not permitted in breeding programs. Breeders prefer to verify that the correct genes are passed on by putting the two cats together to mate physically.
Test tube methods such as IVF and embryo transfer are potentially useful is a queen can ovulate, but is unable to carry a litter to term or if the queen can ovulate but the sperm cannot reach the eggs. The ova can be removed and fertilised using test tube methods. The fertilised eggs could be implanted back into the queen or into a surrogate mother who has ovulated but not been impregnated by a stud cat. Once again there is a possibility of genetic mix-ups if the surrogate mother has been impregnated.
Egg donation isn't really an issue in cats, because it is used for the benefit of infertile females who want to have babies. An infertile female cat doesn't benefit a breeding program by passing on someone else's genes when it is the infertile cat's genes which are needed.
PARTHENOGENESIS AND EGG FUSION
While much attention is currently turned to cloning an individual from a body cell, there is another form of cloning, or at least of producing an individual from donor cells without fertilization. Human fertility studies have shown that an egg cell can be made to divide and develop without it being fertilized by a sperm. This would create an individual whose genes all come from a single parent.
Egg cells contain only half the number of chromosomes that are found in body cells (because the other half of the set is contributed by the sperm cells). The "clone" would not contain any back-up copies of genes to compensate for faulty ones. The offspring would be female (since they only inherit an X gene) and would contain different combinations of the mother's genes. They could look quite different e.g. different eye colour/fur colour because the mother may carry traits which are masked by other traits. They would not be true clones, but they could possibly produce clones themselves.
The drawback is that an offspring whose cells contain only half the normal complement of chromosomes would probably be sterile because it would be unable to form egg cells. This is because it only has one set of chromosomes, not the normal two sets - the chromosome set cannot be split any further. Either the unfertilized egg must be induced to make a second set of chromosomes (which would be identical to the original set) or the egg must be fused with a second egg cell. If the chromosomes spontaneously doubled in the unfertilized egg, the individual would be homozygous (true-breeding) for every gene and trait. If it went on to produce offspring by the same method, those offspring would be identical to it. Barring any spontaneous mutation, they would be true clones. This is parthenogenesis (virgin birth) and is seen in aphids.
Fusing 2 eggs from the same donor would provide 2 sets of chromosomes, with a little genetic variation since each egg gets a slightly different mix of genes when it is formed. The offspring would be female, but not identical to the mother. This sounds straightforward but there is a problem. In humans, it appears that a few genes need to be inherited from a male parent even though they are not on the Y chromosome. If those genes are inherited from the female parent (the "wrong" parent), abnormalities apparently occur. So far, no-one knows whether this is true for cats as well as for humans, or whether it is true for embryos created by egg-fusion where both parents are female.
CLONING AND THE CAT FANCY
Can the cat fancy keep up with reproductive technology and what impact do these techniques have on pedigree cats? Cloning and artificial insemination carry plenty of implications for the cat fancy. For example, a show-stopping neuter could be cloned and the unneutered clone used for breeding. Or an excellent stud cat might be cloned (or sperm might be banked) and its clones or stored sperm might be used in several breeding lines, passing its genes on to far more offspring than that single stud cat could have fathered in its lifetime. A cat rendered infertile by an accident could be cloned and the clone (or banked sperm) could pass the genes on.
Cells or banked sperm from a deceased cat could be used many generations after the cat has died. Genes which have accidentally been bred out could be re-introduced. Breeds which produce small litters could be propagated more quickly using clones, IVF and surrogate mothers. Suddenly there is no apparent limit to inter-generational matings, back-crossing and litter sizes (where litters are spread across several surrogate mothers)!
Because the DNA of the clone is identical to the DNA of the donor but in a younger body, this can lead to more inter-generational matings - both planned and accidental (if record-keeping is poor). A female who has offspring fathered by a clone could, in essence, be mating with someone from a previous generation. If clone embryos are frozen before re-implantation, she could be mating with a cat which died years or decades previously. Back-crossing is already used in selective breeding of animals (seeThe Pros and Cons of Inbreeding), cloning increases the number of generations a breeder can back-cross to.
Back-crossing might slow down the accumulation of genetic changes by using "old" genes from previous generations instead of using "new" (possibly slightly changed) versions of those genes. Sticking with "old" genes slows down the rate of change. At worst, the gene pool could stagnate, missing out on beneficial minor mutations. At best, random harmful mutations might be avoided and a type would be "fixed" for longer. Unless cloning becomes the norm, there is little danger of gene pool stagnation since there will be far more cats reproducing in the conventional manner. However, selective breeding has already greatly reduced the gene pool of some animals and breeds, in which case cloning and breeding from clones will worsen the situation by reducing genetic variation.
A breeder might want to perpetuate a mutation but there is a limit to the number of females a stud cat can mate with or to the number of kittens a female cat can have. For example what if a female gives birth and then contracts such a serious uterine infection after giving birth that she has to be spayed to save her life? Her genes could be saved by creating a clone. What if a potential cat had already been castrated by a previous owner? Cloning will create an uncastrated cat which can pass on its genes in the normal way.
Sometimes the desirable trait is rare so that breeders want to increase the number of cats carrying that trait . Cloning means that several copies exist and can be used as foundation stock in several breeding lines at the same time, overcoming the physical limitation of having a single cat. This will get a breed going much quicker than with just one foundation stud. Cloning and genetic engineering provides the potential for designer cats.
Neutering and spaying will no longer be a dead end. In one sense this could be a lifeline in preserving a rare trait, but it also means that pedigree cats sold with a neutering/no-breeding agreement could be cloned to create a fertile individual used by a backyard breeder.
The impact on pedigrees will be many and varied and potentially serious. Although reputable breeders will abide by registry regulations or seek special dispensation for certain activities e.g cloning a genetically important stud cat killed in a freak accident, there will be unscrupulous individuals who will take advantage of the new techniques, especially as the cost comes down.
There will have to be limits if pedigrees are to be valid and breed records maintained. How will the clones be identified on the pedigree? Is it necessary to identify which clone sired which kittens since all the clones are identical? Should there be restrictions on the use of clones because of inbreeding concerns? What of the problem of premature ageing because a 2 year old clone contains 12 year old chromosomes?
Reproductive technology is a Pandora's Box. There are no simple solutions to the potential impacts of these techniques, but hopefully an awareness of the possibilities will allow cat breeders and owners to make their decisions wisely.
CLONING TO SAVE A SPECIES - THE CHEETAH & RUSTY SPOTTED CAT
In January 2003, India announced plans to clone cheetahs to help restore the Indian sub-continent's cheetah population (which has been wiped out in India). India asked Iran to provide cheetahs for cloning. The Asiatic cheetah, once found throughout Southwest Asia and the South Asian subcontinent, is now restricted to about 50 individuals in a few locations in Iran, with possibly a few in Pakistan and Afghanistan. Scientists at Hyberabad's Centre for Cellular and Molecular Biology plan to create the clones from live cells from the Iranian cheetahs. Scientists are aware that it will not be an easy experiment and will take a lot of research, dedication and hard work. They plan to use a leopard as surrogate mother to produce the cloned cheetah cubs.
Domestic cats have successfully carried transplanted embryos of endangered wild small cat species (see below) and domestic cattle have successfully carried cloned calves of endangered bovine species so there a leopard could theoretically carry a cheetah cub. If they use an egg cell from the leopard, the cubs' mitochondrial DNA will be from the leopard, however, the offspring will be a cheetah (have nucleus DNA from cheetah cell donor), not a leopard/cheetah hybrid.
Following the birth of domestic cat clone Cc in 2001, Martha Gomez's team at the Audubon Center for Research of Endangered Species (New Orleans, Louisiana, USA) cloned the African wild cat in 2003, using domestic cats as surrogate mothers. The results were 2 males (a third male did not survive) and 5 females that will now be bred in the conventional manner. They were created using African wildcat DNA with the domestic cats used as egg donors and surrogate mothers. The next step is to demonstrate that the clones breed normally.
In January 2005, Gomez's team announced their attempts to clone the rare Black-Footed Cat (a southern African small cat) and the intention to clone the Rusty Spotted Cat (a small cat from India and Sri Lanka). In 2004, cloned Black-Footed Cat embryos, were implanted into a domestic cat surrogate mother, but none survived to full term. It is possible that the two species are too distantly related for the surrogacy to work. To clone the Rusty Spotted cat, preserved cells from a deceased US zoo specimen will be used. There are 13 rusty spotted cats in captivity and their wild counterparts are endangered by hybridisation with domestic cats. Their ability to hybridise means they should be closely enough related that domestic cat surrogates can be used.
Cloning could also be used to help endangered tigers. Because lions and tigers can interbreed, tiger DNA could be implanted into a lion donor egg and lion surrogate mother. However, a more obvious and less expensive method would be to stop zoos and private menageries from breeding trash tigers (where they indiscriminately mix different subspecies) including white tigers (heavily inbred mutants) and to concentrate on breeding tiger subspecies. This would prevent the need for cloning tigers.THE "END OF EXTINCTION" SCENARIO
This note has been added for those interested in the cloning of extinct species.
There are several obstacles to be overcome in resurrecting extinct species through cloning. Firstly, there is the problem obtaining intact DNA. The DNA in preserved specimens is fragmented; many preserving processes damage the DNA. Reassembling fragmented DNA may not be possible; errors in the reassembly equate to mutations and will most likely be lethal. It might be possible to "borrow" DNA from a suitable closely related living species to compensate for damaged stretches of DNA. Even where good tissue samples are available, there is the problem of surrogate mothers. Cloned embryos must be implanted into compatible mothers (e.g. same gestation period).
To resurrect an extinct animal, both males and females must be cloned in order to breed. If only one gender is available for cloning, it may be possible to cross a clone with an individual of a closely related species and then back-cross the crossbreed offspring to the original (pure-bred) clone. Over five to seven back-crossings will result in an almost pure-bred population. There might not be a compatible, closely related species to hybridise with. It might be possible to "borrow" DNA from a suitable closely related living species to do a sex-change on a cloned embryo. This is less of an issue in reptiles where sex determination depends on incubation temperature.
To establish a successful breeding population, there must be genetic diversity i.e. as many different individuals as possible must be cloned. If this is not possible, cross-breeding may be needed. The clones would not have adults of their own species to learn from and might not learn certain skills e.g. hunting, social behaviour. There also needs to be a habitat to release the resurrected species into, otherwise they will end up as novelties in zoos and safari parks.
Recently extinct species where good quality DNA samples are preserved in tissue banks and where closely related species can provide surrogate mothers are more likely to be successfully resurrected. There is some hope of finding preserved DNA in frozen mammoths and using elephants as surrogates. Some extinct subspecies of big cat might be candidates for resurrection as they have living relatives. At our present level of knowledge, a lack of undamaged DNA means species such as moas, dodos, warrahs, quaggas and thylacines will remain extinct for the foreseeable future.
CLONING AND INHERITANCE
Note: This diversion from the main feline topic is included at the request of correspondents requesting information on how cloning could affect evolution.
Over the years there have been several theories of inheritance, only one of which works in reality.
Maternal Impression: This theory says that an unborn offspring is affected by the mother's environment i.e. if the pregnant animal is housed in close proximity to outstanding examples of her own species, she will somehow impress their characteristics on the foetus even if she was mated to a mediocre stud. If the pregnant mother is exposed to a bad example, these will be transmitted to her foetus. It was used to explain human birth defects i.e. a baby born with a hare-lip was due to maternal impression when the pregnant mother being "startled by a rabbit". The only things that can cause a form of maternal (environmental) impression are certain drugs and environmental chemicals (teratogens).
Paternal Impression (Telegony): This theory says that a female's first mate will affect all of her subsequent offspring, even those fathered by different mates. Basically this says that if a female is mated to an outstanding stud for her first litter, his characteristics will turn up in all her later litters fathered by other studs. Dog breeders attempting to breed terriers which strong jaws believed that mating a terrier bitch to a Bulldog stud would cause all her later puppies (sired by ordinary terrier studs) to have stronger jaws. It is also the basis of the myth that if an female animal is mis-mated to a poor quality male she will be "ruined for life" i.e. she will always bear poor quality offspring due to paternal impression.
Lamarckism: Characteristics inherited by an individual in his or her own lifetime will be passed on genetically to the offspring. If this actually worked, generations of declawing would already have resulted hereditary clawlessness in cats. The only instance in which it can work is if a cell mutation affects the egg-forming cells in the ovaries or the sperm-forming cells in the testes of the parent - the mutation would not show up in the parent, but would show up in the offspring. This is a germ-line mutation because it affects the germ (egg/sperm) cells and can be inherited.
Mendelism: (Greatly over-simplified explanation) All individuals carry information (now called genes) which is passed on and shuffled into new combinations in their offspring. This is the basis of modern genetics and is well documented elsewhere.
Cloning would bypass Mendelism. With no sperm and egg meeting to contribute information to the new individual, genes do not get shuffled into new combinations. A form of Lamarckism would happen where acquired damage to DNA during the donor's lifetime would be passed on to the offspring (mentioned in the earlier example of a skin cell with damaged DNA). Change would occur, but it would be based on cell mutation, not on gene shuffling. It would occur at a far slower rate. Cloning is comparable to parthenogenesis with the exception that both males and females can be cloned.
SOCIAL ISSUES OF HUMAN CLONING
Note: This diversion from the main feline topic is included at the request of correspondents requesting information on how cloning could affect human society.
Many of the above can be applied to humans as well as to cats. The underlying biology and genetics are essentially the same. In November 2002 it was announced that the world's first cloned baby was due. The clone was said to be of an "important, wealthy personality". Scientists warned other hopeful parents that only 1% to 6% of cloned embryos survive to birth, and that many of those die soon after due to malformations. In humans, the mother could be at risk from choriocarcinoma, a form of cancer unique to humans. Choriocarcinoma develops from the trophoblast (the embryonic part that invades the womb wall and becomes the placenta). Poorly regulated genes controlling placental growth are believed to be the cause of this. The additional risk is because those genes remain switched on in cloned embryos and cause abnormal growth of tissues.
Even if the potential problems of rare cancers are overcome in human cloning, the cultural, moral and social issues are different. In humans, there is already a problem of "hidden incest" due to sperm donor insemination - i.e. half-brother and half-sister may marry unwittingly. Because of the incest taboo, cloning presents social and moral consequences for humans which are not an issue in cats.
Consider a human society where the incest taboo means a woman (Ms X) cannot marry her male cousin. For whatever reason, the cousin is cloned. The clone is carried by a surrogate mother not related to the family. Genetically, the cousin's clone is identical to the cousin. Socially, the clone is not related to Ms X. Does the incest taboo still hold?
The question is does the incest taboo apply to the cousin's body (and therefore not to his clone) or to the cousin's genes (and therefore to the clone)? If human cloning occurred, women could find themselves mating with a clone who is, genetically at least, their own grandfather! The concept of incest would have to be redefined and how would a clone fit into a family tree? As an offspring of the donor? As the donor's identical twin? As the offspring of the surrogate mother (a woman could carry her own clone)? The same problem applies to feline pedigrees and to human family trees.
If the clones are not tracked somehow, a woman could find herself marrying a genetic copy of her own father or grandfather; a son could end up dating a younger clone of his own mother or grandmother. Is it still incest to have sex with a younger version of your own parent? Legal and religious prohibitions would become a minefield; couples might have to produce "pedigrees" before being permitted to marry.
Who would be cloned? The fittest? This would be most beneficial for the gene pool. The richest? This is more likely. Unless the wealth is inherited, rich people are often older people; they might want to achieve a form of immortality through cloning, but premature ageing would be a danger here. For example: a 40 year old is cloned. When he is 70 and his clone is only 30 both could be suffering the same age-related diseases due to the problem of cellular age/biological age. Accumulated cell damage would be passed on from donor to clone and, if the clone passes the genes on to his/her children, this would weaken the gene pool. As long as clones are in the minority, the damage will be limited but once in the gene pool, the damaged genes may be passed from one generation to the next and cause problems many generations later.
The social and moral considerations would be more worrying to humans than the genetic considerations.