What type of inheritance is characterized by dominant traits related to the X chromosome?

• A. Autosomal Dominant
• B. X-linked Dominant
• C. Y-linked
• D. Autosomal Recessive

Answer: (B)

The correct answer is B, X-linked Dominant, because this type of inheritance occurs when a dominant allele is located on the X chromosome. In X-linked dominant inheritance, only one copy of the mutated gene—present on either of the X chromosomes in a female (XX) or on the single X chromosome in a male (XY)—is sufficient to express the trait or disorder.

Males are generally affected more severely because they possess only one X chromosome, so any mutation on that X leads to expression of the trait. Females, having two X chromosomes, may exhibit the trait if they have the mutation on either one or both X chromosomes. A prime example of an X-linked dominant condition is Rett syndrome, which primarily affects females.

This inheritance pattern can result in a higher prevalence of the trait in females compared to males, and it often manifests regardless of whether the affected individual has a father with the condition, since fathers pass their Y chromosome to sons. The mother has a 50% chance of passing the affected X chromosome to her children, meaning both sons and daughters can inherit the trait, making the pattern distinct from autosomal inheritance.

In contrast, autosomal dominant traits do not involve the sex chromosomes, while Y-linked traits are exclusively