Kaplan Nursing Entrance Practice Exam

If a homozygous dominant parent is crossed with a homozygous recessive parent, what phenotype might appear in the F2 generation that is absent in the F1 generation?

1. Recessive phenotype

2. Dominant phenotype

3. Intermediate phenotype

4. Co-dominant phenotype

The correct answer is: Recessive phenotype

In a cross between a homozygous dominant parent and a homozygous recessive parent, the F1 generation will display only the dominant phenotype because the dominant allele masks the expression of the recessive allele. However, when the F1 generation is allowed to self-fertilize or is crossed with another F1 individual, the resulting offspring, known as the F2 generation, can exhibit a variety of phenotypes in accordance with Mendelian inheritance patterns. In this scenario, the homozygous recessive phenotype, which was absent in the F1 generation, re-emerges in the F2 generation. This occurs due to the segregation of alleles during gamete formation, leading to a combination of genotypes among the F2 offspring. As a result, the presence of two recessive alleles can bring about the recessive phenotype in some of the F2 individuals. This is a classic example of how recessive traits can be hidden in one generation but can reappear in subsequent generations when the right genotypic combinations occur.