Ecology and Evolution

FALL 2026

Population Genetics

• the study of allele frequencies and how they change over time in a population

Genotype

a combonation of alleles at a locus (genetic feature)

Phenotype

a visible attribute

Locus

specific DNA location

Hardy Weinberg Equation

• is a null equation (base-line)' and can be used to find allele frequencies or phenotypes or individual organisms possessing a trait

• if = 1 there is no evolution is occurring in the population

• if the equation does not equal one than there IS evolution occurring

• p²+2pq+q²=1 and p+q=1

Calculation of allele frequencies and genotype frequencies

Genetic Drift

: random change in allele frequencies due to pure chance

• can cause fixation or loss of alleles

• MORE SEEN IN SMALL POPUALTIONS

Fixation of Alleles

two variants of the same allele compete, and one wins becoming “fixated”/permanent while the other is lost

Bottleneck Event

: any circumstance that causes a severe reduction of a population size

• followed by a huge loss of alleles

• TEMPORARY

Founder Effect

: when a population colonizes a new location and the original allele frequencies begin to differ

• the small changes in allele frequencies compound over time

Fitness

: reproductive success of a genotype or phenotype within a population/ species

Average EXCESS of fitness

: determining factor of what phenotypes or genotypes increase or decrease over time from one population to then next

Mutation

change in a genotype

Genetic Drift

: random change of allele frequencies due to pure chance

• loss or fixation

• occurring more in smaller populations

Gene flow

: introduction of new alleles into a population (migration)

Selection

: natural selection of phenotypes as they are more aligned with the environment

Label the Hardy-Weinberg equation and tell me how to use it

p² + 2pq +q² = 1 and p+q =1

• p² : homozygous dominant

• 2pq : heterozygous

• q² : homozygous recessive

• p : dominant trait

• q : recessive trait

: p+q=1 helps me find an allele frequency

p² + 2pq +q² = 1 helps me find phenotypes or info for an individual

always find p and q first!!!