Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

If the first son of the woman described in (a) is affected, what is the probability that her second son is affected?

Key Concepts

X-linked Recessive Inheritance

X-linked recessive inheritance refers to genetic conditions that are associated with genes located on the X chromosome. Males, having one X and one Y chromosome, are more likely to express these disorders if they inherit a mutated X chromosome. Females, with two X chromosomes, can be carriers if they have one mutated X, but typically do not express the disorder unless both X chromosomes are affected.

Probability in Genetics

Probability in genetics involves calculating the likelihood of inheriting specific traits based on parental genotypes. In the case of X-linked disorders, the probability of a son being affected can be determined by considering the mother's genotype and whether she is a carrier or affected. This involves using Punnett squares or basic probability rules to assess the chances of inheritance.

Carrier Status

Carrier status refers to individuals who possess one copy of a mutated gene but do not exhibit symptoms of the associated disorder. In X-linked recessive conditions, a mother who is a carrier has one normal X chromosome and one mutated X chromosome. This status is crucial for determining the risk of passing the disorder to her offspring, particularly sons, who will inherit their X chromosome from her.