Have you ever wondered why pretty much all Calico cats are female? Well, it’s all about the power of genetics! So here's a little genetics 101 that will help explain this very interesting phenomenon. If you'd like to read more information to help build your foundation in genetics then have a read at this basepaw's blog!
Every animal has pairs of different chromosomes, this is species specific! Cats have a total of 19 pairs of chromosomes; whereas, dogs, have 39 pairs of chromosomes (and giraffes have a wooping 30 pairs!). On each pair of chromosomes, you have alleles which basically has genes which will code for what your pet inherits. Now, you have XX chromosomes and XY chromosomes; XX is what makes a female kitty female and XY ,"Y" is what makes a male a male.
Coat color is often carried ("expressed") on these genes and this is referred to as Sex-linked. With female kitties, what geneticists see is this inactivation of a random X chromosome; a term often called Lyonization. The entire process is a bit long to explain but we’ll make it simple.
Look at the picture below: The black X on the left shows that X chromosome will express the black fur coat, whilst the on the right you have an X chromosome encoding for the orange coat color. So what’s happening is that the second X chromosome becomes a Barr body; which is a very condensed chromosome that is inactive. (think of this as a scrunched up paper that’s not useful).
Well, what about male cats? Can’t they be tortoiseshells as well? Without a doubt, yes they can! These are rare cases though which often occur due to misdivision resulting a male cat gaining an extra X-chromosome making them code XXY. Interesting fact: In human males, this term is referred to as Klinefelter syndrome and often leave both male cats and male humans infertile.
Now, wasn’t this interesting phenomenon just Meoowwgic!