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.

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

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.

Answer 2

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 3

To determine the expected genotypes of the man and woman's biological children, let's use a Punnett Square. The man and woman are both heterozygous for the photic response trait, which means they have the genotype Hh.

Punnett Square:

| H | h |
--------------------
H | HH | Hh |
--------------------
h | Hh | hh |

From the Punnett Square, we can see that there are four possible genotypes for the offspring: HH, Hh, Hh, and hh.

Now let's determine the corresponding phenotypes for each genotype:

- HH: This genotype represents individuals who sneeze when exposed to bright sunlight.
- Hh: This genotype also represents individuals who sneeze when exposed to bright sunlight.
- Hh: This genotype, again, represents individuals who sneeze when exposed to bright sunlight.
- hh: This genotype represents individuals who do not sneeze when exposed to bright sunlight.

So there are three possible phenotypes: individuals who sneeze when exposed to bright sunlight (HH and Hh), and individuals who do not sneeze when exposed to bright sunlight (hh).

Now let's calculate the expected percentages for each phenotype:

- Individuals who sneeze (HH and Hh): Since HH and Hh both represent individuals who sneeze, the probability of having this phenotype is 3/4 or 75%.
- Individuals who do not sneeze (hh): Since hh represents individuals who do not sneeze, the probability of having this phenotype is 1/4 or 25%.

Therefore, the expected percentages of the phenotypes are 75% for individuals who sneeze and 25% for individuals who do not sneeze when exposed to bright sunlight.

Answer 4

To answer this question, let's start by understanding the Punnett square and how it helps predict the genotypes and phenotypes of the offspring.

A Punnett square is a visual tool used to determine the possible combinations of alleles from each parent and predict the genotypes and phenotypes of their offspring. In this case, we have a man and a woman who both carry the alleles H and h for the photic response trait.

Here's how we can use a Punnett square to predict the genotypes of their biological children:

1. Write the alleles of one parent (man) along the top of the Punnett square, and the alleles of the other parent (woman) along the left side.

Man's alleles: H h
Woman's alleles: H h

2. Combine one allele from each parent by drawing lines from the man's alleles to the woman's alleles.

H h
______________________
H | HH Hh
______________________
h | Hh hh

Now, let's determine the possible genotypes and phenotypes of the offspring based on the Punnett square:

1. HH: This genotype represents individuals with two dominant alleles. They will always exhibit the photic response trait, sneezing when exposed to bright sunlight.

2. Hh: This genotype represents individuals with one dominant allele (H) and one recessive allele (h). They will also exhibit the photic response trait, sneezing when exposed to bright sunlight.

3. hh: This genotype represents individuals with two recessive alleles. They will not exhibit the photic response trait and will not sneeze when exposed to bright sunlight.

Identify the possible phenotypes and their expected percentages:

From the Punnett square, we can see that there are three possible genotypes: HH, Hh, and hh. To determine the expected percentages, we need to consider the ratio of each genotype:

- HH: There is one possible way to obtain this genotype, which is 1 out of 4 (25%) in a square starting with 2 rows and 2 columns.
- Hh: There are two possible ways to obtain this genotype, which is 2 out of 4 (50%).
- hh: There is one possible way to obtain this genotype, which is 1 out of 4 (25%) in a square starting with 2 rows and 2 columns.

So, the expected percentages of the phenotypes in the offspring are as follows:

- 25% chance of having the genotype HH, resulting in the phenotype with the photic response and sneezing when exposed to bright sunlight.
- 50% chance of having the genotype Hh, resulting in the phenotype with the photic response and sneezing when exposed to bright sunlight.
- 25% chance of having the genotype hh, resulting in the phenotype without the photic response and not sneezing when exposed to bright sunlight.

I hope this explanation helps you understand the Punnett square and how to predict the genotypes and phenotypes of the offspring.