Question

In the seawolf (a rare hypothetical animal), the dominant allele R causes solid tail color, and the recessive allele r results in white spots on a colored background. For coat color, a separate trait, the black coat color allele B is dominant to the brown allele b, but the B and b alleles can only be expressed if the animal has an M_ genotype at a third gene locus. Animals that are mm are yellow regardless of which allele from the B locus is present. A mating between a solid yellow-tailed male seawolf and a solid brown-tailed female seawolf produces 16 offspring with the following tail phenotypes: six solid yellow, two spotted yellow, three solid black, one spotted black, three solid brown, and one spotted brown. What is the MOST likely genotype of the male parent?

Answer 1

Answer:

The most likely genotype of the male parent is RrBbmm.

Explanation:

First of all, we have 3 genes and 6 alleles:

For color pattern:

- RR or Rr: Solid tail color

- rr: Spotted tail

For coat color:

- BB or Bb: Black coat color

- bb: Brown color

Expression of gene B/b depends on M:

- MM or Mm: B/b is expresed.

- mm: B/b is not expresed, yellow coat.

So, a cross between a solid yellow-tailed male and a solid brown-tailed female was made, and the offspring was:

- 6 solid yellow

- 2 spotted yellow

- 3 solid black

- 1 spotted black

- 3 solid brown

- 1 spotted brown

Total: 16

If it was produced all possible phenotypes, it means that parents have to be carriers of R/r, B/b, and M/m alleles. Male parent is yellow, so he has to be mm for this gene, but for the two other alleles he should be heterozygous:

RrBbmm

And female parent is solid brown-tailed, so she has M allele, (probably heterozygous), and Rr and bb (color brown),, like this:

RrbbMm

When these two genotypes are crossed, 8 gametes are generated for each parent, and 64 possible combinations. This cross in the attached Punnett Square.

As a result, the phenotypicial ratios are in the attached table and they are the same as the reported in the question:

Punnett Square

- 24 (6) solid yellow

- 8 (2) spotted yellow

- 12 (3) solid black

- 4 (1) spotted black

- 12 (3) solid brown

- 4 (1) spotted brown

Total: 64