In humans, hemophilia A (OMIM 306700) is an X-linked recessive disorder that affects the gene for factor VIII protein, which is essential for blood clotting. The dominant and recessive alleles for the factor VIII gene are represented by H and h. Albinism is an autosomal recessive condition that results from mutation of the gene producing tyrosinase, an enzyme in the melanin synthesis pathway. A and a represent the tyrosinase alleles. A healthy woman named Clara (II-2), whose father (I-1) has hemophilia and whose brother (II-1) has albinism, is married to a healthy man named Charles (II-3), whose parents are healthy. Charles's brother (II-5) has hemophilia, and his sister (II-4) has albinism. The pedigree is shown below.

Determine the probability that the first child of Clara and Charles will be a

i. boy with hemophilia
ii. girl with albinism
iii. healthy girl
iv. boy with both albinism and hemophilia
v. boy with albinism
vi. girl with hemophilia <>

Key Concepts

X-linked Recessive Inheritance

X-linked recessive inheritance refers to genetic conditions that are associated with genes located on the X chromosome. In this mode of inheritance, males (XY) are more likely to express the disorder because they have only one X chromosome. Females (XX) can be carriers if they have one affected X chromosome and one normal X chromosome, but they typically do not express the disorder unless both X chromosomes are affected.

Autosomal Recessive Inheritance

Autosomal recessive inheritance involves genes located on non-sex chromosomes (autosomes). For an individual to express an autosomal recessive condition, they must inherit two copies of the mutated gene, one from each parent. Carriers, who have one normal and one mutated allele, do not show symptoms but can pass the mutated allele to their offspring, making it crucial to understand family history when assessing risk.

Punnett Square Analysis

A Punnett square is a tool used in genetics to predict the genotypes of offspring from parental crosses. By organizing the alleles of each parent, it allows for the visualization of potential genetic combinations and the probabilities of inheriting specific traits. This method is particularly useful for determining the likelihood of offspring having certain genetic conditions, such as hemophilia or albinism, based on the parents' genotypes.