Cat Genetics

I’m teaching a bio course this term and I’ve been looking for ways to engage students in lab type activities given that we can’t go into a lab. When someone sent me an article about why most of the human genetic traits we like to use in genetics lessons are inaccurate I was, shall we say disappointed. I knew that many of them weren’t as simple as we taught but to see so many fall to inaccuracy was tough. If you’re interested you can check out the article “Myths of human genetics“. On the upside, the article also links to one about a lesson on cat genetics. This is right up my alley as I’m a bit of a cat person and my cats have their own instagram account (@arielandtempest) which I’ve been using to document their journey’s through life as well as to share information about adoptable animals from the local area.

I’ve simplified the activity by Christensen (2000) a bit to suit my audience and I’ll try to post the whole activity up here when I finish it. But in the meantime, here is some cat coat genetics.

My intention is to use mainly currently adoptable animals but I admit that finding a long hair, white cat in need of a home would take a lot more time than I have. So why did I want a long haired, white cat. Well let’s break it down.

First, let’s talk Mendelian genetics. Traits that follow Mendelian patterns have one form that is clearly dominant to the other. Mammals (and many other groups) have two copies of each chromosome. I describe a chromosome as one of the recipe books on your recipe book shelf (yes, I realize that is becoming outdated with apps and other online recipes but students still follow it). Each recipe book, or each chromosome, carries the recipes (genes) for a bunch of different items (proteins). We get two copies of all of our chromosomes (except X and Y), one from each genetic parent. So now we have two recipe books that each contain the same dishes, but there may be differences. One book might have chocolate chip cookies, while the other one may have oatmeal chocolate chip cookies. In Mendelian genetics, one of those recipes will be dominant over the other (which would then be considered recessive).

In cats, the recipe for short hair is dominant over long hair. This means that the only way the recipe for long hair shows up is if both recipe books have that exact recipe (or, in genetic speak, two copies of the same allele). Conversely, a short hair cat could have two copies of the short hair allele, or it could have one short hair and one long hair allele. This is because the short hair is dominant and will overrule the long hair allele if it is present.

We use letters to symbolize the different alleles. Conventionally, we use a capital letter for the dominant allele, and a small letter for a recessive allele. Letter choice for some things is standardized but for the purposes of my intro class, the students can choose which letter they use. So we could use L = short hair and l = long hair. So the cat above is ll because it has long hair.

So now let’s think about the white fur. White is a dominant allele. It’s kind of interesting too because if you have even one copy of the W allele, it will block all the other colour genes. Because the cat above only needs one copy of the W allele to be white we can’t actually tell what the second allele would be.

Therefore, the above cat is llW_.

Now the fact that this cat has two different eye colours is a different set of genes that I may go into at a later date. But I think that’s good for now. My intention is to bring in some other coat colour traits for future posts so stay tuned if you are interested.