[Cats] Saturday's trivia answer

[MJ]

Question:

What conditions need to be met for a pair of cats to produce 
calico-colored kittens?

Answer:

It's a rather interesting process that produces calicos.  It's all in 
the genes.  Calico is a coat color and not a breed, of course, so the 
inherited genes that control coat color and pigment are responsible. 
The gene that determines coat color in cats is contained in the X 
chromosome.  Since females inherit two X chromosomes, they can inherit 
two coat color genes.  White (as we saw before in terms of deaf white 
cats) is not a color - it's a result of the pigment gene shutting off 
during fetal development.

Coat colors in cats can be only two colors: black and/or red, and the 
variations of these colors are basically due to the degree of density 
of these colors (controlled by the dense pigment gene).  Which is why we 
see combinations of chocolate/cream/white or blue/cream/white in the 
dilute calico/tortie.

Okay.  So, in order to produce one or more calicos in a litter, you must 
have one parent pass on the red color gene and have the other parent 
pass on the black gene.  The chances of tortoiseshell kittens being born 
to these parents are higher than that of them producing calicos, because 
it's all a matter of chance as to if/when the pigment gene inactivates 
in hair cells and produces a white hair instead of the inherited color.

So, why are calicos and torties primarily female?  Well, a cat has to 
inherit two X chromosomes to be two colors (particolor).  Females are 
genetically XX, and males are genetically XY.  This means that any males 
who are born calico or tortie must be genetically XXY - and will be 
sterile (a side effect of having XXY chromosomes, or Klinefelter's 
syndrome).

BTW, did you know that all cats are genetically tabbies?

-Marie