Question

In gerbils, the pathway for pigment production has the following characteristics: the dominant T allele converts a colorless precursor into a colorless intermediate which is then converted by the dominant E allele into a yellow pigment. Neither of the recessive alleles for these two loci produces a functional gene product. What portion of yellow progeny would you expect from matings between TTee X ttEe?

Answer 1

From a cross between TTee and ttEe gerbils, 50% of the offspring are expected to be yellow, because they require at least one dominant T allele from the TT parent and one dominant E allele from the Ee parent.

Step-by-step explanation:

In gerbils, determining the portion of yellow progeny from a cross between TTee and ttEe requires understanding of epistasis, which is the interaction between genes where one gene masks the expression of another. Since the T allele is needed to convert the precursor into an intermediate and the E allele converts this intermediate into yellow pigment, both alleles are necessary for yellow coloration.

The TTee parent can only pass on alleles T and e to the offspring, and the ttEe parent can pass on alleles t and either E or e. From this, we can set up a Punnett square to predict the offspring's genotypes and conclude that any offspring must inherit a T from one parent and at least one E from the other parent to be yellow.

When we perform the cross, we have:

• For the T locus: Tt (all offspring will be heterozygous since one parent is homozygous TT and the other is tt)
• For the E locus: Ee or ee (there is a 50% chance the offspring will receive an E allele from the ttEe parent)

To have a yellow offspring, we need at least one E allele, therefore 50% of the offspring will be yellow (TtEe), while the other 50% will be colorless intermediates (Ttee).