Hemophilia A Inheritance Probability

This question requires understanding the principles of X-linked recessive inheritance.

Understanding Hemophilia A

Hemophilia A is an X-linked recessive disorder. This means the gene causing it is on the X chromosome. Males have XY chromosomes, and females have XX. A male with one affected X chromosome will express the disorder. A female must have the affected gene on both X chromosomes to be affected, but can be a carrier if she has it on only one.

Genetic Cross Setup

• Mother: Carrier for hemophilia A. Her genotype is $X^HX^h$, where $X^H$ represents the normal allele and $X^h$ represents the hemophilia allele.
• Father: Genetically normal male. His genotype is $X^HY$.

Calculating the Chance for Male Offspring

To find the probability of having a male offspring with hemophilia, we need to consider the chromosomes passed from each parent to a son:

• A son inherits the Y chromosome from his father.
• A son inherits one X chromosome from his mother.

The mother ($X^HX^h$) can pass either her $X^H$ allele or her $X^h$ allele to her offspring.

• If she passes $X^H$, the son's genotype is $X^HY$ (normal).
• If she passes $X^h$, the son's genotype is $X^hY$ (affected with hemophilia).

Since the mother has a 50% chance of passing on the $X^h$ allele, the probability that her male offspring will have hemophilia is 50%.

Punnett Square Analysis

The Punnett square shows the possible genotypes of the offspring. For male offspring (inheriting Y from the father), the possibilities are $X^HY$ (normal) and $X^hY$ (affected). Each has an equal probability, leading to a 50% chance of an affected male.