Kaplan Nursing Entrance Practice Exam

In the context of genetics, what is the expected phenotype ratio from a monohybrid cross?

1. 3:1

2. 1:2:1

3. 9:3:3:1

4. 1:1

The correct answer is: 3:1

In a monohybrid cross, where one trait is being examined, the expected phenotype ratio is indeed 3:1. This classic ratio derives from the work of Gregor Mendel, the father of modern genetics, who conducted experiments with pea plants. In a monohybrid cross, typically involving two heterozygous parents (both carrying one dominant and one recessive allele), the potential offspring can display two different phenotypes based on the dominant and recessive traits. When these two heterozygous parents are crossed, the resulting genotype of the offspring can be represented as follows: - 1 homozygous dominant (AA) - 2 heterozygous (Aa) - 1 homozygous recessive (aa) In terms of phenotype, the homozygous dominant and heterozygous offspring will display the dominant trait, while only the homozygous recessive will show the recessive trait. This leads to three offspring exhibiting the dominant phenotype for every one offspring that exhibits the recessive phenotype, resulting in the 3:1 ratio. The other ratios mentioned in the choices refer to different genetic scenarios. The 1:2:1 ratio is specifically indicative of the genotypic ratios from a monohybrid