Question

A cross between a purebred black mouse and a purebred white mouse yields all black F, offspring. These black F, sibling mice are crossed to produce an F generation. You observe the following F phenotypic ratio: White: 22 Black: 175 Gray: 114 a. Draw out the crosses described above, showing the genotypes of the parents, F. and F. b. You cross white mice from the F, generation X black mice from the F, generation. What is the probability of getting black offspring from this cross?

Answer 1

The cross between a purebred black mouse and a purebred white mouse suggests incomplete dominance, with the F1 generation being all black (BW genotype) and the F2 generation showing a phenotypic ratio corresponding to a complex inheritance pattern. To determine the probability of black offspring from an F2 white and black mouse cross, information on the genotypic ratio of the black mice is needed.

Step-by-step explanation:

To answer the question about the cross between a purebred black mouse and a purebred white mouse that yields all black F1 offspring, and the F2 generation phenotypic ratio of White: 22, Black: 175, Gray: 114, we need to consider a form of incomplete dominance, since we observe a third gray phenotype.

For the F1 generation, all offspring are black, which suggests that black (B) is dominant over white (W) and gray is a result of heterozygosity (BW). The parental generation (P) would therefore have genotypes BB (black) and WW (white). The F1 generation, which is all black, would have the genotype BW.

For the F2 generation, crossing two BW genotyped mice, we would expect the following phenotypic ratio: 1 BB (black): 2 BW (gray): 1 WW (white). However, the observed phenotypic ratio is roughly 9 (black): 6 (gray): 3 (white), suggesting that a 9:3:4 ratio occurs due to a more complex inheritance pattern.

When crossing the F2 white (WW) mice with the F2 black mice (which could be BB or BW), we cannot determine the probability of black offspring without knowing the genotypic ratio of the black mice. Assuming all black mice are BB, all offspring would be black. If the black mice are a mix of BB and BW, then the probability of a black offspring will depend on the presence of the B allele from the black parent.

Since this calculation relies on the precise genotypic makeup of the F2 black mice, which we do not have, we cannot calculate the exact probability without further information.

Answer 2

The probability of getting black offspring from a cross between white mice and black mice is 50%.

Step-by-step explanation:

To determine the probability of getting black offspring from a cross between white mice from the F1 generation and black mice from the F2 generation, you need to know the genotypes of the mice involved. The white mice from the F1 generation are heterozygous for the black color gene (Bb), and the black mice from the F2 generation can be either homozygous black (BB) or heterozygous black (Bb). When you cross a heterozygous black mouse with a black mouse, there is a 50% chance of getting black offspring. This is because the heterozygous black mouse can pass on either a black allele or a white allele, and the black mouse can only pass on a black allele.