Kaplan Nursing Entrance Practice Exam

What is the likely result of crossing a homozygous red plant with a white plant?

1. All offspring will be red

2. All offspring will be white

3. Some offspring will be red

4. No red offspring will be produced

The correct answer is: All offspring will be red

The result of crossing a homozygous red plant with a white plant is that all offspring will be red if the allele for red is dominant over the allele for white. In genetics, a homozygous red plant means it has two identical alleles for the red trait (let’s represent the red allele as 'R' and the white allele as 'r'). When a homozygous red plant (RR) is crossed with a white plant (rr), all offspring produced will inherit one allele from each parent. This results in all offspring having the genotype Rr, which expresses the red phenotype due to the dominance of the red allele. Therefore, all offspring will exhibit the red trait, making the conclusion unequivocally linked to the principles of Mendelian genetics regarding dominance and recessiveness. A clearer understanding of dominance helps in predicting the outcomes of such genetic crosses. The other options assume varying ratios of red and white phenotypes, which contradict the genetic principles at play in a simple cross involving a homozygous and a homozygous recessive organism.