Genetics and Environment — Why the First Cloned Cat Looked Nothing Like Her Mom and Other Stories

Photo by Cong H on Unsplash

In 2001, Texas A&M University made history with the birth of a kitten named CC.

CC was the first ever cloned cat. Her gene mother was a calico cat named Rainbow.

CC?

CC wasn’t calico. At first they thought they had an oops…how did they clone a calico cat and get a tabby and white. Genetic testing, though, confirmed that CC (short for Copy Cat) was, indeed, identical to the donor.

So, what was going on here?

X-Chromosome Inactivation, Otherwise Known as Why There Are So Few Male Tortoiseshells

Cats have a fairly compact genome. And at some point in their evolution, the color genes ended up…on the sex chromosomes.

Or rather, on the X chromosome. Yup, a cat’s coat color is determined by genes on the X chromosome.

In this specific case, we’re looking at the gene which determines whether a cat’s coat is red-based or black-based. This gene lives on the X chromosome, so female cats have two copies, but genetically normal male cats only have one (all male tortoiseshells are, in fact, intersex).

So, there’s an issue with carrying double genes when you only need one set. All female mammals have a mechanism called XCI (X-chromosome inactivation). This mechanism turns off one X chromosome in each cell.

You can see where this is going. Calico and tortoiseshell cats carry both genes, for red and black. Depending on which X chromosome gets randomly turned off in which skin pigmentation cell, the cell produces red and black. For some reason, likely related to how mammals make sure that internal organs get the same activated X, they clump together making those oh so pretty red and black patterns.

For some reason, every single one of CC’s skin cells got the black gene active. This may happen more than we thing as we don’t generally gene test our tabby cats.

CC also had different white spotting pattern. Let’s look at that next.