Wednesday, 3 August 2011

Genetics: Make Me Orange!

So last time we learned that all cats are basically all black cats, but the interaction of other genes or gene modifiers change cats from basic black into the multitude of colours you see in the feline population.

The orange gene is the one I'm looking at today.

Cats carry the orange gene on their X chromosome, it's a sex linked gene.The presence of the gene masks a cat's black colouring -often called brown or seal in the cat fancy- and replaces it with orange, often called 'Red' in the cat fancy.

Boy cats have one X chromosome, from their mother, and one Y, from their father, and so can have one orange gene (from their mother) Boy cats can therefore either be black (in the absence of the orange gene) or orange (if it is present) but not both.

Girls, on the other hand, have two X chromosomes, one from their mother and one from their father, and so can have two, one or no orange making genes. If they have none, the cat will be a black cat. If they have two, the cat will be an orange cat. If they have the orange making gene on ONE chromosome only, and the other chromosome does not have it, then that's when you get a tortoiseshell cat.
Boy cats only have one X chromosome, remember, so can only have the orange making gene, or not have it, they cannot be tortie (but they will still have an underlying colour (brown etc) that they can pass on genetically- this one caught me out with our last litter!)  Girls can have the make me orange gene on one and not have it on the other. This is why all torties are female. Unless there's an underlying major chromosomal difference, such as an XXY cat... which is WAAAAAY beyond the scope of this blog!

None of my cats are orange or tortoiseshell. None of them have the make me orange gene. So it doesn't explain their colouration... we'll get onto that soon. Lisl and Lottie are torties though... because I mated my 'brown' (lilac!) cat Indigo with an 'orange' (apricot) cat Harry. And very beautiful they are too.

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