Brona McVittie reports :: June 2006

I named our last cat after the famous Irish black beer because her mottled fur coat reminded me of a settling pint of Guinness. Had I £25 000 to spare, and were Guinness still alive, I might consider getting her cloned. But I’d be a little miffed with my new moggy because it’s unlikely she would resemble my beloved puss. The first cloned cat, Carbon Copy, was created in Texas from a calico cat like Guinness. But the kitty didn’t turn out to be a ‘carbon copy’ despite having identical DNA to her genetic ‘mother’ Rainbow.

This can be partly explained by an epigenetic phenomenon known as X-inactivation. Calico cats are always female, which means they have two X chromosomes in every cell. The gene for orange coat colour is located on the X chromosome, but there is another version (allele) of this gene that results in black fur. In female cats (XX), one X chromosome gets switched off (inactivated) in every cell, so if a female inherits one of each allele (orange and black) then her coat will exhibit patches of both colours.

The process of inactivation is random, which is why cloning a calico cat will never produce the same pattern. In the case of Carbon Copy, she was created from an egg cell that had its nucleus replaced with one from Rainbow. Although the cell from which Carbon Copy was cloned had one inactive X, the developmental programme reactivates both X-chromosomes, and the process of inactivation recurs in a random manner. This results in an entirely different coat pattern even when two individuals are genetically identical.

The handful of millionaires that have banked the cells of their prized pets may be paying over the odds for an animal which has no guarantee of being the same. Instead of paying over £400 for the privilege and £50 annual maintenance, plus the rather exorbitant cloning fee when their pet pops its clogs, perhaps they might be persuaded to take in one of the many millions of abandoned pets that will otherwise be euthanised.