Question

In the mating of an Aa female and an Aa male, the genotypic outcome predicted by a Punnett square is ________.

1) three-quarters Aa and one-quarter AA

2) All offspring will have the genotype Aa

3) one-quarter AA, one-quarter aa, and one-half Aa

4) one-half AA and one-half aa

5) three-quarters Aa and one-quarter aa

Answer 1

The predicted genotypic outcome from the mating of Aa individuals is one-quarter AA, one-quarter aa, and one-half Aa, following Mendelian inheritance with a genotypic ratio of 1:2:1.

Step-by-step explanation:

In the mating of an Aa female and an Aa male, the genotypic outcome predicted by a Punnett square is one-quarter AA, one-quarter aa, and one-half Aa. These expected genotypic proportions come from the random fertilization of gametes where each parent contributes either an 'A' or an 'a' allele. By constructing the Punnett square, you can see that there are four potential allelic combinations: AA, Aa, aA (which is the same as Aa), and aa. Since Aa and aA are genetically the same, we combine these to observe that roughly 25% of the offspring would be AA, 50% would be Aa, and 25% would be aa, resulting in a genotypic ratio of 1:2:1. This is a classic example of Mendelian inheritance, where the predicted phenotypic outcome for the dominant trait would be expressed in a 3:1 ratio because both AA and Aa exhibit the dominant phenotype.