Trimethylaminuria is a genetic condition in humans which cau

Trimethylaminuria is a genetic condition in humans which causes them to have a \'fishy\' odor. This is because they have a defect in the enzyme flavin-containing monooxygenase 3 (FMO3). This enzyme converts trimethylamine to trimethylamine N-oxide. Trimethylamine N-oxide is odorless, but trimethylamine has a fishy odor (and indeed is what gives fish their fishy smell, but also protects the fishes\' proteins from destabilization. The allele that produces the functioning form of the enzyme (use the symbol F) is dominant, and the nonfunctioning form of the enzyme is produced by a recessive allele (f). The alleles follow the rules of Mendelian inheritance. In a population of 500 individuals the allele frequencies are F=0.8 and f=0.2. Assuming that there is no immediate selection on this trait, what are the genotype frequencies? How many individuals are there with each genotype?

Solution

The gene coding for functional enzyme if F and the gene coding for nonfunctional enzyme is, f; F is dominant over f.

The frequency of F = 0.8 and the frequency of f = 0.2

The frequency of FF genotype in the population is = 0.8*0.8 = 0.64

The population frequency with FF genotype is = 0.64*500 = 320

The frequency of Ff genotype in the population is = 2*0.8*0.2 = 0.32

The population frequency with FF genotype is = 0.32*500 = 160

The frequency of ff genotype in the population is = 0.2*0.2 = 0.04

The population frequency with ff genotype is = 0.04*500 = 20