|MadSci Network: Genetics|
Well, in the case of your cat "Miss Kitty" the calico it is due to what is called Barr Body, or an inactive X-chromosome. Females have 2 X-chromosomes, but since the cell only needs to have one active, it shuts the other one down so it is not in use. Now for calico's, the gene for black or orange fur lies on the X-Chromosome. A female cat may inherit one gene for Orange fur from her mother, and a gene for black fur from her father. When the zygote(a fused sperm and egg) start to divide to form a kitten, the embryonic cells will inactivate one X-Chromosome, but this occurs randomly. Then at a later stage of development, these emryonic cells give rise to skin and tissue cells that have the same x-chromosome inactivated giving multiple populations of cells that have the same barr body(inactivated X-chromosome). So there may be clusters of cells that have an active X-Chomosome that express the orange color, yet another cluster of cells may have the black expressing X-chromosome active. That is why calicos have those random black and orange patches of fur and are almost always female. There are sometimes gentic mutations that can cause males to express calico patterns such as XXY inheritance. There may be white fur as well, but that is probably caused by a gene on another chromosome. Now, males also have one X-Chromosome(and one Y-Chromosome), but the X is always active because it is the only one present. So males for the most part don't have calico patterns, except in the rare case explained above. The patterns on the fur, and other shades of fur are again probably due to color genes being expressed on other chromosomes. Patterns in embryonic development, and subsequently tissues are very organized. That is why cats with the genes to express say the Tabby patterns are all very similar in pattern. Minor variations occur due to size of the cat, genes for fur color and just individual cell differentiations between one cat and another, but the pattern is still roughly the same. Your cat's litter inherited lots of different color patterns from each parent, but some colors are dominant over others which is why you saw a mixture. But the question is, are the two calico's female? I bet they are. Hope this answers your question. Mark Sullivan
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