A woman's father has ornithine transcarbamylase deficiency (OTD), an X-linked recessive disorder producing mental deterioration if not properly treated. The woman's mother is homozygous for the wild-type allele.

What is the woman's genotype? (Use D to represent the dominant allele and d to represent the recessive allele.)

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 pattern, 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 they are homozygous for the recessive allele.

Genotype and Alleles

A genotype is the genetic constitution of an individual, represented by the alleles inherited from their parents. In this case, 'D' represents the dominant allele and 'd' represents the recessive allele. The woman's genotype will depend on the alleles she inherited from her parents, particularly considering her father's X-linked condition and her mother's homozygous wild-type status.

Homozygous vs. Heterozygous

Homozygous refers to having two identical alleles for a particular gene, while heterozygous means having two different alleles. The woman's mother is homozygous for the wild-type allele (DD), meaning she can only pass on the dominant allele (D) to her offspring. The woman, therefore, must inherit one X chromosome from her father (which carries the recessive allele d) and one X chromosome from her mother (which carries the dominant allele D), resulting in a heterozygous genotype (Dd).