Question

When exposed to bright sunlight, some people involuntarily sneeze. This reaction is known as a photic response. It is controlled by a single gene with two alleles, H and h. A man and a woman who sneeze when exposed to bright sunlight are both heterozygous for the photic response trait. Draw a Punnett Square using the allele symbols H and h to show the expected genotypes of the man and woman’s biological children. Identify all possible phenotypes of the offspring and their expected percentages.

Answer 1

The correct answer is explained below:

Step-by-step explanation:

• According to the question,
• The dominant allele for the photic response gene is: H
• The recessive allele for the photic response gene is: h.
• It is said that both the man and the woman are heterozygous for the photic response trait, that is, both of them have the Hh genotype.
• Both sneeze when exposed to bright sunlight, hence both of them show the photic response phenotype.
• This means the photic response trait is a dominant trait.
• Gametes produced by both the man and woman are: H and h.
• Mating the man with the woman, we get offspring with the following genotypes and phenotypes.

H h

H HH Hh

Photic Response Positive Positive

h Hh hh

Photic Response Positive Negative

• From the above Punnett square we get,
• Percentage of offspring expected to show photic response trait =
  `(3)/(4) = 75` %.
• Percentage of offspring expected to not show any photic response trait =
  `(1)/(4) = 25` %.