Genotype Frequencies flashcards 9-10

Homozygous Dominant

A genotype with two identical dominant alleles, typically written as AA.

Heterozygous

A genotype with one dominant and one recessive allele, written as Aa.

Homozygous Recessive

A genotype with two identical recessive alleles, written as aa.

Genotype Frequencies

The proportion of each genotype (AA, Aa, aa) in a population. They must sum to 1: f(AA) + f(Aa) + f(aa) = 1.

Allele Frequencies (p and q)

The relative proportion of specific alleles (e.g., A as p, a as q) in a population. p + q = 1. Derived from genotype frequencies as p = f(AA) + \frac{1}{2} f(Aa) and q = f(aa) + \frac{1}{2} f(Aa).

Hardy
Weinberg Equilibrium

A theoretical state where genotype frequencies in a population remain constant across generations because specific conditions are met (large population, random mating, no evolutionary forces). Under HW equilibrium, frequencies are f(AA) = p^2, f(Aa) = 2pq, and f(aa) = q^2.

Calculating Genotype Frequencies (Direct Counting)

To calculate genotype frequencies by directly counting the number of individuals with each genotype (x for AA, y for Aa, z for aa) in a sample of n individuals: f(AA) = \frac{x}{n}, f(Aa) = \frac{y}{n}, f(aa) = \frac{z}{n}.

Relationship between Allele and Genotype Frequencies

Allele frequency p is the frequency of the homozygous dominant genotype plus half the frequency of the heterozygous genotype (p = f(AA) + \frac{1}{2} f(Aa)). Similarly, q = f(aa) + \frac{1}{2} f(Aa).