In a particular plant height is under the control of a singl

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%

Solution

Answer: (C) 70%

Penetrance is the proportion of individuals carrying a particular allele of a gene that expresses an associated trait. Penetrance of a disease causing mutation is the proportion of individuals with the mutation that exhibit the symptoms of the disease.

If we cross two heterozygous plant: Aa * Aa, the proportion of the expressing dominant tall allele A is 0.5.

Again, considering the phenotype, 120 out of 200 expresses the dominant trait.

So, proportion of tall phenotype = 120/200 = 0.6

But, the proportion of the A allele = 0.5

So, proportion of A allele that is expressing = 0.6 * 0.5 = 0.3

Therefore, penetrance = 0.7 = 70%