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

Assuming this is a recessive trait.

HH = doesn't express trait

Hh = carrier

hh= express trait

Genotype:

1 HH

2 Hh

1 hh

1:2:1

Phenotype:

3:1

Doesn't express: express

25% chance of expressing trait.

Answer 2

Cont.

Assuming this is a dominant trait.

HH = Express trait

Hh = Express trait

hh= doesn't express trait

Genotype:

1 HH

2 Hh

1 hh

1:2:1

Phenotype:

3:1

Express: doesn't express

75% chance of expressing trait.

The wording of the question indicates autosomal dominant. The trait is expressed although both are heterozygous.