Hardy-Weinberg Principle

Gene pool

• combination of all genes (including alleles) present in a reproducing population or species

• large gene pool has extensive genomic diversity and is better able to withstand environmental challenges

• can be any population - frogs in a pond, trees in a forest, or people in a town

gene or allele frequency

• relative frequency of an allele (variant of a gene) at a particular locus in a population

• fraction of all chromosomes in the population that carry allele over total population or sample size

EX: in population of pea plants purple (W) and white (w) alleles can be found

hardy-weinberg equilibrium

• population in which allele frequencies do not change over time = genetic equilibrium (Hardy-Weinberg equilibrium HWE) / stable non-evolving state.

Factors that disrupt genetic equilibrium

in a large random-mating population, genotype + allele frequencies remain constant in the absence of any evolutionary influences from one to another generation

• mutations

• natural selection

• nonrandom mating

• genetic drift

• gene flow

mutations

• disrupt equilibrium of allele frequencies by introducing new alleles into a population

• permanent changes in the gene sequence of DNA

  • alter genes + alleles leading to genetic variation in a population

natural selection & nonrandom mating

• result in gene frequencies

• occurs because certain alleles help or harm reproductive success of organisms that carry them

Genetic drift

• occurs when allele frequencies grow higher or lower by chance and typically takes place in small populations

Gene flow

• occurs when breeding between two populations transfers new alleles into a population

FORMULAS

Allele Frequency

• p + q = 1

p: dominant allele frequency (A)

q: recessive allele frequency (a)

Genotype Frequency

• p²+2pq+q²=1

p²: Homozygous dominant (AA)

2pq: Heterozygous dominant (Aa)

q²: Homozygous recessive (aa)