Question

In a particular plant, height is under the control of a single gene that has two alleles: the dominant A (Tall) and the recessive a (Dwarf). A cross of two heterozygous tall plants produces 200 offspring, of which 120 are tall. What is the penetrance of the dominant height allele?

A. 50%
B. 60%
C. 70%
D. 80%
E. 90%

Answer 1

In the given plant genetics scenario, the penetrance of the dominant height allele is 80%, as 120 out of the expected 150 tall offspring were observed to be tall in a cross of two heterozygous plants that resulted in 200 total offspring.

Step-by-step explanation:

The student is inquiring about the penetrance of the dominant height allele in a plant genetics scenario. In the scenario, a cross of two heterozygous tall plants results in 120 tall offspring out of 200. To determine the penetrance, which is the proportion of individuals with a given genotype who exhibit the phenotype, we refer to the expected Mendelian ratio for a cross between two heterozygous individuals, which is 3:1 for the dominant trait to the recessive trait. This means out of four offspring, three are expected to be tall. However, in this student's experiment, only 120 of 200 offspring were tall, indicating incomplete penetrance.

To find the penetrance, we calculate the percentage of observed tall offspring (120) out of the expected number. Since we expect 3 out of every 4 offspring to be tall in the case of complete dominance and 150 tall offspring (200 total × 0.75), the penetrance is the observed number of tall offspring divided by the expected number: 120/150 × 100% = 80%.