Two genes interact to produce various phenotypic ratios among F2 progeny of a di

Question

Two genes interact to produce various phenotypic ratios among F2 progeny of a dihybrid cross. Design a different pathway explaining each of the F2 ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F2 progeny produced by crossing wild-type F1 organisms with the genotype RrTt.

15/16 black : 1/16 white

A. One copy of any dominant allele results in black. The absence of either dominant alleles results in white.

B. The only way to produce black is to have at least one dominant allele at one specific locus and homozygous recessive alleles at the other locus. The second dominant allele functions as a suppressor; therefore, if both dominant alleles are present, it will suppress the expression of the first.

C. At least one copy of both dominant alleles is required for black pigment. The absence of either dominant allele results in white.

Explanation / Answer

A ratio of 15:1 indicated duplicate dominant interaction. Its a kind of epistasis wherein both genes produce the same products/color.

                                    Enzyme or prodct of gene R

Colorless precursoe ------------------------------------------------------> COlored product

                                 Enzyme or prodct of gene T

Only the prganism with genotype rrtt will produce white color

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