Question

FMO3 is an enzyme that helps break down a chemical in humans, trimethylaamine, that produces the smell of rotting fish. The gene for FMO3 is located on chromosome 1. The functioning form of the enzyme is coded for by a dominant allele, and the nonfunctioning form of the enzyme is coded for by a recessive allele. Individuals with the nonfunctioning from of the enzyme have trimethylaminuria, also known as fish odor syndrome. Neither Maggie nor Mark has the fish odor syndrome, but their daughter Melissa does. If Maggie and Mark have another baby, what is the chance that child will also have fish odor syndrome?

Answer 1

The fish odor syndrome is a recessive disorder, and thus, requires two alleles in order to manifest the condition. In the given case, both the parents do not exhibit the syndrome, however, their daughter does. It signifies that both the parents are carriers, and thus, are heterozygous.

In such situations, the heterozygous parents exhibit a 25 percent chance of having a child with the condition, while 75 percent chance of having a non-affected child. Thus, they have zero percent chance of exhibiting a child with fish odor syndrome.