Question

"In humans, photic sneezing (sneezing when exposed to sunlight) and wet ear wax are both the result of dominant alleles, P and E, respectively. If a woman who is unaffected by photic sneezing but is heterozygous for wet ear wax marries a man who is heterozygous for photic sneezing but has dry ear wax, what percentage of their children would likely both sneeze when exposed to sunlight and have dry ear wax?"

Answer 1

The correct answer is explained below:

Explanation:

• According to the question, photic sneezing and wet ear wax are dominant traits.
• The dominant and recessive alleles for photic sneezing is represented by P and p respectively.
• Therefore, PP and Pp genotype individuals are photic sneezing positive and pp genotype individuals are photic sneezing negative.
• The dominant and recessive alleles for wet ear wax is represented by E and e respectively.
• Therefore, EE and Ee genotype individuals have wet ear wax and ee genotype individuals have dry ear wax.
• The woman is said to be unaffected by photic sneezing and is heterozygous for wet ear wax, so her genotype would be ppEe.
• The gametes produced by the woman are: pE and pe.
• The man is said to be heterozygous for photic sneezing  and has dry ear wax, so his genotype would be Ppee.
• The gametes produced by the man are: Pe and pe.
• Mating the man and the woman we get the following offspring,

                                                           pE                            pe

                                   Pe                 PpEe                        Ppee

Photic sneezing/Ear wax          Positive/Wet             Positive/Dry

                                   pe                 ppEe                        ppee

Photic sneezing/Ear wax          Negative/Wet            Negative/Dry

• The genotypes and the phenotypes of the offspring obtained by the mating is represented in the Punnett square shown above.
• The percentage of children who would sneeze when exposed to sunlight, that is, photic sneezing positive and have dry ear wax $=\frac{1}{4}= 25$%.