Question

Two normal parents have three normal children: one son and two daughters. Their son and one of their daughters marry and also have normal children. Their second daughter, Mary, marries a man with a rare, recessive blood disorder. They have two children, and both children develop the blood disorder. What were the genotypes of Mary's parents?

Answer 1

Answer: Either one of her parent or both have heterozygous as trait.

Explanation:Heterozygous refers to when you inherited a particular form of gene from each parent. Heterozygous occurs when two allele of a specific gene locus are different. Heterozygous

Means one of each type of allele. Mary parent are (AA) (Aa) respectively.

Answer 2

Answer: Mary's parents' genotype are Aa and AA.

Explanation: Suppose the recessive blood disorder has a genotype of aa.

Mary's husband's genotype, as he has the trait, is aa. Both of their children also have it, so they are aa as well. To have a child with this genotype, Mary must have been a carrier, so her genotype is Aa.

Now, for Mary to be a carrier and since none of her siblings has the disorder,  one of her parents must be heterozygous for the trait (Aa), while the other is homozygous for the trait (Aa).

In other words, Mary's parents' genotypes are Aa and AA.