Let’s Take a Bet: Almost All Tri-Colour Cats Are Females!

Awwwww, cute cats! Is this why you are reading this post now, cat-lovers?

Cats are such fun companions to have around. They sometimes make you laugh so hard and other times really annoy the hell out of you.

Surely by now you have noticed all those beautiful coat colours on our furry friends. Although you might secretly keep a coat colour ranking in heart, you completely ignore that preference list and think your cat at home is the most beautiful creature in the entire world. Am I right? But that’s okay, we are all guilty of it.

Personally, I’m not picky on this matter, but one type of coat absolutely captures my attention: the tri-colour coat. These cats covering in white, orange and black patches, regardless of their breeds, are called Calico or tortoiseshell cats.

Calico cat with orange and black patches on her coat. Image via Flickr, by Carmen.

Interestingly, these tri-colour cats are almost always females. You can confidently bet on this with a guaranteed win. (Just don’t try this on Sphynx cats, trust me!)

You might be puzzled now, thinking how is coat colours linked to genders? How is this a guaranteed win?

There are seven genes that controls the coat colour, giving cats white, grey, or chocolate hair, but only the orange/black patches are tale-telling. This is because the gene contributing to orange hair is on X-chromosome, which is a sex chromosome.

Like humans and other mammals, female cats have two X-chromosomes (XX), while males have only one X and one Y-chromosome (XY). Now because there are two versions of this orange gene, either active or inactive, female cats can have one version on each X-chromosome, giving them the potential to develop both orange and non-orange hair.

But how are the patches formed?

Aha, that’s exactly what captures my attention the most. The patches are there because of a phenomenon called the X-inactivation. In short, females (XX) need to randomly shut down one X-chromosome when growing up, because females have one extra copy of X, compared to males (XY).

Female cats with different versions of the orange gene on each X-chromosome, randomly shut down either the orange or the non-orange version of the gene.

If the non-orange gene is silenced and the orange gene is active, then that patch of coat would be orange in colour; if the orange gene is silenced and the non-orange gene is active, the coat would have a black patch.

On the other hand, male cats only have one copy of X-chromosome, carrying either the orange or the non-orange gene, which gives only one colour coat.

There you go, this is why all Calico or tortoiseshell cats are female, because males simply cannot produce the third colour in the coat with only one copy of X-chromosome.

To add a bit more fun, the seven coat colour genes actually interplay to produce the final coat colour. The orange and black patches could be diluted by another gene! Just like this cutie below.

This Calico cat has diluted orange and black patches because of another gene. Image via Flickr, by Cliff

As you might have guessed, the X-chromosome inactivation process might be more complicated than what is described in this post. Here is a bit more on this topic if you would like to read more.


3 Responses to “Let’s Take a Bet: Almost All Tri-Colour Cats Are Females!”

  1. Jasmine Rhodes says:

    I love all cats, but MY CAT IS THE MOST BEAUTIFUL CREATURE IN THE WORLD.

    Thanks for this cat post, Jing! It fulfilled my hopes for a cat post perfectly!

  2. Jing Deng says:

    Thanks for reading my post, Yvette! Really glad you enjoy it.

  3. Yvette H. says:

    This was a very interesting read Jing! Whilst I’ve always held a place in my heart for calico coat patterns on our sweet furry friends, I’ve never stopped to think how the patches can occur. Thanks to you now I know 😀