Expert: Norman Auspitz - 3/20/2011

Question
QUESTION: I am fostering a young (under 1 yr) female blue short-haired cat for our local animal shelter so she could have her litter and all could be eventually neutered and adopted. She looks so much like a Russian Blue, gold/green eyes, blue silky double coat with the silver tippings, mauve colored paw pads, etc. She was turned in as a "stray" so I figured she'd have a Heinz 57 variety of offspring. To my surprise she gave birth to 5 kittens all blue like herself, with the 2 males being somewhat lighter gray and slightly fluffier.  What are the genetic odds of that??  Could she have been bred to another Russian Blue and then owner could not keep for some reason.  What kind of random pairing could produce all blue kittens from a blue female??

ANSWER: Sheila,

If the two males are "light gray", are they not blue?  Are their paw pads mauve to slate gray?

OK, the density gene is what is called the dilute gene. The wild allele has no affect on coat color, whereas the allele that reduces density will give you blue, but it has to be homozygous (i.e. both parents either have to be dilute or carry dilute).  In this case, given the litter, the odds are that both parents were also homozygous for the dilute gene. Certainly the mama is homozygous and if the males in question are, indeed, blue (read light gray), they also were probably homozygous for the dilute allele.

As to hair length, the long hair allele of hair length is also a recessive, so both parents have to be long haired or at least carry long hair to have "fluffy" kittens. The litter appears to be all short hairs, so one may suggest mama is probably not carrying the long hair allele.

As to your speculation about coming from a breeder, it is, certainly, possible, but, probably, not likely.

Please let me know if this is sufficient explanation, or you need any of the above further explained.

Best regards... Norm



---------- FOLLOW-UP ----------

QUESTION: Just a little more clarification. What are the other colors of male (homozygous--dilute) cats that could have fathered the kittens in addition to a male colored just like her? I know a buff/cream cat has the dilute gene but wouldn't that add in the red gene and make some torties?? And once again, what are the odds of this if it was a random wild pairing out on the streets?  I'm thinking this is pretty unusual for a random pairing, but maybe I'm wrong??  BTW all four kittens have the same mauve to slate blue colored paw pads. Thanks so much for your info.

Answer
Sheila,

The odds of a blue male with no tabby markings mating with this girl in the wild are astronomically small!!!!!!!!  It is very, very unlikely this was an accidental breeding with a random male.

If there were a cream male, then females would be blue creams!  Males could be blue or cream. So, yes it would add in the red gene (also called "sex-linked orange")

Also, the fact that there are no tabby markings is also very, very remote given the wild population!!!!!!!!!!

Best regards... Norm.