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In a certain breed of dog, the alleles B and b determine black and brown coats respectively. However, the allele Q of a gene on a separate chromosome is epistatic to the B and b color alleles resulting in a gray coat (q has no effect on color). If animals of genotype B/b ; Q/q are intercrossed, what phenotypic ratio is expected in the progeny

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Answer:

12 gray , 3 black, 1 brown

Explanation:

If Q allele of a gene on a separate chromosomes is epistatic to the B (black) and b (brown) color alleles, in cross between two animals with genotypes BbQq produces 12 gray coat color, 3 black coat color and 1 brown coat color animals.

                                        BbQq      x      BbQq

                                   Gray coat        Gray coat

                   BQ                  Bq                 bQ                 bq

   BQ    BBQQ(gray)  BBQq(gray)   BbQQ(gray)   BbQq(gray)

   Bq     BBQq(gray)   BBqq(Black)  BbQq(gray)   Bbqq(Black)

   bQ     BbQQ(gray)  BbQq(gray)   bbQQ(gray)   bbQq(gray)

   bq     BbQq(Gray)   Bbqq(Black)  bbQq(gray)    bbqq(brown)

So the phenotypic ratio is  Gray : Black : Brown

                                        =      12  :      3   :      1

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