Kaplan Nursing Entrance Practice Exam

If one parent is homozygous dominant and the other is homozygous recessive, which phenotype might appear in the F2 generation?

1. Dominant phenotype

2. Recessive phenotype

3. Codominant phenotype

4. Incompletely dominant phenotype

The correct answer is: Dominant phenotype

In a situation where one parent is homozygous dominant (having two dominant alleles) and the other is homozygous recessive (having two recessive alleles), the first generation of offspring (F1 generation) will all inherit one dominant allele from the dominant parent and one recessive allele from the recessive parent. This results in all F1 individuals expressing the dominant phenotype because the dominant allele masks the effect of the recessive allele. When these F1 offspring are crossed to produce the F2 generation, the genetic combinations will provide the opportunity for different phenotypes to arise. The F2 generation will exhibit a phenotypic ratio that stems from the segregation of the alleles during gamete formation in the F1 generation. Depending on the specific ratios obtained from the genetic cross, the potential for both dominant and recessive phenotypes exists. However, because one of the parents is homozygous dominant, the dominant phenotype is expected to occur more frequently. Thus, in the F2 generation, the presence of the dominant phenotype is guaranteed due to the homozygous dominant nature of one parent contributing that gene, which is why this answer is the most appropriate. Recessive phenotypes can also emerge but will be less common relative to