I used to have a tri-colored cat. She had black, white and ginger patches. She was a little mad and she also ate my neighbor's pet rabbit but that's another story. What was I saying? Oh, yeah, I really like this question as it's a good example of how gene inheritance works. It's quite complicated but it's pretty cool when you understand it all.
OK, so lets think about genes and inheritance. We all know that animals (including humans) get half their genes from their mum and half from their dad, right? Our genes decide pretty much everything about us and in cats, genes decide what color their fur will be. Now, like humans, cats have two copies of most genes (one from dad, one from mum). The combined effects of these two genes determine whether our eyes are blue, whether we have ginger hair, long legs, tiny brains etc. etc.
Now, there aren't actually two copies of every gene. To explain this we need to think about sex chromosomes. Sex chromosomes decide whether a baby will be a girl or a boy. You always get an X chromosome from your mother but can get an X or a Y from the father. So half of all babies will end up with two X's and the other half will have an X and a Y. XX=girl, XY=boy. It just happens that the Y chromosome is very little and is missing lots of the genes that are on the X. So while girls have two copies of all the genes found on the X chromosome, boys only have one copy of those genes missing from the Y chromosome as they only have one X chromosome.
So back to the cats. Most of the genes involved in deciding what a cat's coat will look like are found on the autosomes (normal chromosomes that have nothing to do with sex). However, one of the color genes is found on the X chromosome. This gene is the orange fur gene. It can come in two forms. I should explain at this point that not all genes are created equal. Sometimes one gene is dominant, this means that it will over-rule whatever the other gene is trying to do. We call the other gene recessive and it only gets a say if it is partnered with another recessive gene that isn't strong enough to over- rule it. So we call the dominant form of the orange gene O (a big O) and this gene tries to make a cat orange. The recessive version of the gene is called o (a little o) and this stops a cat from being orange, letting some black or brown genes choose the color of the cat.
So male cats can either have O or o, and will therefore be either
orange or black/brown. Females cats have two copies of the orange
gene and can be OO (orange), oo (black). Or they can be Oo. This
means they have both versions of the gene. Now, I know I said
that O could over rule o. So why aren't these cats all orange?
Well, what happens is that, during development of the embryo,
one of the X chromosomes gets turned off in each cell and the
genes on this chromosome don't get to do anything. So different
bits of the cat have different X chromosomes turned on and this
gives them the patchwork effect. Where the O is turned on, they
will be orange and where the o is turned on, they will be black/brown.
You never get this happening in male cats as they have only one
X chromosome and this is switched on in every cell.
