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.

What are the genotypes of the four parents (I-1 to I-4) in this pedigree? <>

Key Concepts

X-linked Recessive Inheritance

X-linked recessive inheritance refers to genetic traits that are carried on the X chromosome. In this pattern, males (XY) are more likely to express the trait because they have only one X chromosome, while females (XX) can be carriers if they have one affected X and one normal X. Hemophilia A is an example of this, where the presence of the recessive allele on the X chromosome leads to the disorder in males and can be passed from carrier mothers to their sons.

Autosomal Recessive Inheritance

Autosomal recessive inheritance involves genes located on non-sex chromosomes (autosomes). For an individual to express a recessive trait, they must inherit two copies of the recessive allele, one from each parent. Albinism, caused by mutations in the tyrosinase gene, exemplifies this inheritance pattern, where both parents must either be carriers or affected for their offspring to exhibit the condition.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance of traits through generations in a family. It visually represents family relationships and the presence of specific genetic traits, allowing for the determination of genotypes based on observed phenotypes. In the context of the question, analyzing the pedigree helps deduce the genotypes of the parents based on the inheritance patterns of hemophilia and albinism in their children.