Question

Two people have a child together. The mother is known to be lactose intolerant, a recessive trait. The father has never exhibited lactose intolerance. The child is also found to be lactose intolerant. What does the child’s lactose intolerance say about its parents’ genetic composition? Explain your answer. Support your answer with a Punnett square and highlight the genetic composition of the child.

Answer 1

Answer:

Father= Aa (heterozygous carrier)

Mother= aa (homozygous recessive)

Lactose intolerant child = aa (homozygous recessive)

Explanation:

Lactose intolerance is an autosomal recessive trait. Let's assume that the recessive allele "a" is responsible for lactose intolerance while the dominant allele "A" gives normal phenotype. The mother is lactose intolerant and therefore, should be homozygous recessive since the recessive disorders are expressed in homozygous genotype only.

The genotype of the mother would be "aa". Father exhibits normal phenotype and therefore, may be homozygous or heterozygous dominant for the trait. However, since they have a "lactose intolerant" child (aa), the father should also have at least one copy of "a" allele. Therefore, the genotype of the father is "Aa" (heterozygous carrier).