A woman with severe discoloration of her tooth enamel has four children with a man who has normal tooth enamel. Two of the children, a boy (B) and a girl (G), have discolored enamel. Each has a mate with normal tooth enamel and produces several children. G has six children—four boys and two girls. Two of her boys and one of her girls have discolored enamel. B has seven children—four girls and three boys. All four of his daughters have discolored enamel, but all his boys have normal enamel. Explain the inheritance of this condition.

Key Concepts

Autosomal Dominance and Recessiveness

In genetics, traits can be inherited in dominant or recessive patterns. A dominant trait only requires one copy of the allele to be expressed, while a recessive trait requires two copies. In this case, the discoloration of tooth enamel may be a dominant trait, as it appears in some children of a parent with normal enamel, suggesting that the mother carries the allele for the condition.

Sex-Linked Inheritance

Some genetic traits are linked to sex chromosomes, particularly the X chromosome. If the condition affecting tooth enamel is X-linked, it would explain why more males in the family exhibit normal enamel, as males have only one X chromosome. This could indicate that the mother carries the allele on one of her X chromosomes, leading to a higher incidence of the trait in her sons.

Punnett Squares and Genetic Probability

Punnett squares are tools used to predict the probability of offspring inheriting particular traits based on the genetic makeup of the parents. By analyzing the genotypes of the parents and their children, one can determine the likelihood of the enamel discoloration appearing in future generations, helping to clarify the inheritance pattern of this condition.