In rats, gene B produces black coat color if the genotype B-, but black pigment

Question

In rats, gene B produces black coat color if the genotype B-, but black pigment is not produced if the genotype is bb. At an independent locus, gene D produces yellow pigment if the genotype is D-, but no pigment is produced when the genotype is dd. Production of both pigments results in brown coat color. If neither pigment is produced, coat color is cream. Determine the genotypes of parents of litters with the following F2 phenotype distribution. a. 9 black, 7 brown b. Provide a genetic explanation for these genotypic and phenotypic results.

Explanation / Answer

Answer:

a. Parents genotype:
BbDd* BbDd

b. Because of complementary gene action in F2 generation 9:7 ratio between Black and Brown pigment is found. Due to epistasis alterration in 9:3:3:1 ration gives 9:7 ratio, the dominant phenotype in rat that have at least one dominant allele of EACH of the two genes; otherwise we get the recessive phenotype. So, the observed ratio in the F2 generation is 9:7

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