A black guinea pig crossed with a guinea pig with albinism produced 12 black offspring. When the albino was crossed with a second black animal, six blacks and six albinos were obtained. What is the best explanation for this genetic situation?
A) Albinism is a recessive trait; black is a dominant trait.
B) Albinism is a dominant trait; black is incompletely dominant.
C) Albinism and black are codominant.
D) Albinism is a recessive trait; black is codominant.

Question

Quizplus · Accepted Answer

The first cross resulted in 12 black offspring, which suggests that the black parent was homozygous dominant for the black trait. When this parent was crossed with an albino parent, all of the F1 offspring were black, suggesting that the albino parent was homozygous recessive for the albino trait. When two F1 black offspring were crossed, the resulting offspring ratio of 6 black to 6 albino suggests that the F1 black offspring were heterozygous for the albino trait, and that albinism is a recessive trait while black is a dominant trait.

A Black Guinea Pig Crossed with a Guinea Pig with Albinism