12-23-2008, 06:47 AM
OK, guess what -- this is a fairly common question on one of my Genetics exams.
The answer is -- there are rare male calico cats. (You are right, and your girlfriend is wrong.) The traditional calico cat color (black and orange spots on a white background) comes from X chromosome inactivation ("Lyonization" ) -- which occurs in a random manner, such that-- in a female cat-- one X containing the orange color is inactivated, versus the other X containing the black color. Whichever X is NOT inactivated, that color appears. It is random as to which X gets inactivated, so you end up with a mosaic of cells. Males, having only one X chromosome, can therefore either have orange spots OR black spots on a white background, but not both. One exception to that is a cat with the equivalent of human Klinefelter's Syndrome, XXY -- this is a male cat but with an extra X chromosome.
More reading:
http://en.wikipedia.org/wiki/Tortoiseshell_cat#Genetics
http://en.wikipedia.org/wiki/Cat_coat_ge...ted_colors
Edit: drat, Stephanie and vp beat me to it...
The answer is -- there are rare male calico cats. (You are right, and your girlfriend is wrong.) The traditional calico cat color (black and orange spots on a white background) comes from X chromosome inactivation ("Lyonization" ) -- which occurs in a random manner, such that-- in a female cat-- one X containing the orange color is inactivated, versus the other X containing the black color. Whichever X is NOT inactivated, that color appears. It is random as to which X gets inactivated, so you end up with a mosaic of cells. Males, having only one X chromosome, can therefore either have orange spots OR black spots on a white background, but not both. One exception to that is a cat with the equivalent of human Klinefelter's Syndrome, XXY -- this is a male cat but with an extra X chromosome.
More reading:
http://en.wikipedia.org/wiki/Tortoiseshell_cat#Genetics
http://en.wikipedia.org/wiki/Cat_coat_ge...ted_colors
Edit: drat, Stephanie and vp beat me to it...