A woman with hypoplasia marries a man with the same defect.

A woman with hypoplasia marries a man with the same defect. A healthy child is born from this marriage. What is the probability of a healthy boy, a girl, in this family?

Enamel hypoplasia is caused by a dominant gene (denote it C), inherited in a form linked to the X chromosome. We write the chromosome with the hypoplasia gene as X C, and the chromosome with the gene that causes the normal development of tooth enamel – as X c.

Since a healthy child is born from a marriage of two persons with hypoplasia, and the male sex is heterogametic, it should be assumed that a woman with hypoplasia is heterozygous and carries in her genotype the gene for healthy enamel – X C X c. Her body produces two types of eggs – X C and X c.

Male with hypoplasia – X C Y. He produces sperm cells X C and Y.

The offspring of this married couple are represented by the following theoretically possible options:

boys with enamel hypoplasia (X C Y) – 25%;

girls with enamel hypoplasia (X C X C and X C X c) – 50%;

boys with normal tooth enamel (X with Y) – 25%.

Answer: the probability of a healthy boy appearing in this family is 25%, and a healthy girl – 0%.