Question

Alkaptonuria is a metabolic disorder which results from an allele (a) that is recessive to the allele for the normal gene (A). Sally has normal metabolism, but her brother and father have alkaptonuria, and her mother has normal metabolism.

A) Give the genotypes of Sally, her mother, father and her brother.
B) If sally's parents have another child, what is the probability that this child will have alkaptonuria?
C) If Sally marries a man with alkaptonuria, what is the probability that their first child will have this metabolic disorder?

Answer 1

Sally and her mother are likely heterozygous (Aa) carriers, while her brother and father are homozygous recessive (aa) for alkaptonuria. The probability of Sally's parents having another child with the disorder is 25%, and if Sally marries a man with alkaptonuria, the probability of their child having the disorder is 50%.

Step-by-step explanation:

Alkaptonuria is an autosomal recessive metabolic disorder that affects an individual's ability to properly metabolize the amino acids phenylalanine and tyrosine. Given that Sally has normal metabolism but her brother and father have alkaptonuria, we can infer the following genotypes:

• Sally must be heterozygous (Aa), as she has a normal metabolism but has a parent and sibling with the disorder.
• Her father and brother must be homozygous recessive (aa) given they express the disorder.
• Her mother must also be heterozygous (Aa), as she has normal metabolism but has produced a child with the disorder.

B) The probability that Sally's parents have another child with alkaptonuria is 25%, as there is a 1 in 4 chance when two heterozygous individuals (Aa) mate.

C) If Sally were to marry a man with alkaptonuria (aa), the probability that their first child will have alkaptonuria is 50%, as there would be a 1 in 2 chance from a heterozygous (Aa) by homozygous recessive (aa) mating.