Wednesday, August 17, 2011

Genetics Punnet Square Challenge?

In cats, Black is dominant over white. Cats that are zygous recessive for white are always white regardless of other genes present. However, a co-dominant linked gene diverts black pigment molocules into a pathway that makes them orange. The non orange allele allows black pigment to be produced. In males with one X chromosome with orange or females with 2 X chromosomes with orange, the entire cat is some shade of orange,providing the cat has at least one black gene. A cat with an orange allele on one X chromosome and a non orange allele on the other, has a mottled pattern of orange and black spots called tortoiseshell. Such a cat is almost always female since only females normally have 2 X chromosomes. The tortoiseshell pattern develops from X chromosome inactivation early in the cat's embryonic development. If the chromosome with the orange allele remains active, the cell's decendants form a patch of orange fur. If the chromosome with the non orange allele is active then the patch is black. Construct a Punnet Square for an orange tom heterozygous at the black locus crossed with a tortishell female heterozygous at the black locus. What is the Genotype and Phenotype ratios for such a mating?

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