Question

In a study of black guinea pigs and white guinea pigs, 100 black animals were crossed with 100 white animals and each cross was carried to an f2 generation. In 94 of the crosses, all the F1 offspring were black and an F2 ratio of 3:1 (black:white) was obtained.In the other 6 cases half of the F1 animals were black and the other half were white. Why? Predict the results of crossing the black and white guinea pigs from the 6 exceptional cases.

Answer 1

Answer:

The genotype of parents for 6 exceptional cross was

Bb * bb

Result for crossing the black and white guinea pigs from the 6 exceptional cases.

Bb * bb

Bb, Bb, bb, bb

Explanation:

Here trait for black guinea is dominant over the trait for white guinea

There is a possibility that for remaining 6 crosses, the genotype of parents would be as follows

Black guinea pig - Bb

White guinea pig - bb

Now when these two genotypes are crossed the following offsprings are produced

Bb * bb

Bb, Bb, bb, bb

Thus, out of four offspring half of them are heterozygous black and remaining half of them are white in color.

Now if these black and white guinea pigs from the 6 exceptional cases with genotype Bb and bb are crossed respectively, then following offspring are produced

Bb * bb

Bb, Bb, bb, bb