Unit 11 - IV. Hardy-Weinberg Principle

Hardy-Weinberg Principle

outlines conditions necessary for genetic equilibrium in a population to be maintained (no evolution)

Allelic frequency

term used to describe how often a particular allele occurs in a population

Gene pool

all of the possible alleles that exist in a population

There are 5 conditions necessary to

maintain genetic equilibrium

1. No

mutations

2. Individuals cannot enter

nor leave a population

Emigration =

leaving

Immigration =

entering

Gene flow

movement of genes from 1 population to another

3. Large population

(prevents genetic drift)

Genetic drift

change in the allelic frequency of a small population due to chance

2 important causes of

genetic drift

Founder’s Effect (reduces genetic variation)

populations started by a few pioneering individuals moving into a new region

Bottleneck Effect (reduces genetic variation)

small group of surviving members of a population breeding together

4. Individuals mate randomly;

no selective breeding

5. No natural selection

(equal survivorship)

Since these conditions can never be met, genetic equilibrium can’t

possibly exist (evolution must occur)

Evolution

• allelic frequencies are never in equilibrium

• gene pools change over time

• phenotype frequencies are changing

Hardy Weinberg mathematical formulas were

used to predict

• allele & genotype frequencies in a population

• (can predict) occurrence of hidden genotypes

Formula for freq. of dominant & recessive alleles in population

p + q = 1

Formula for freq. of genotypes in population

p² + 2pq + q² = 1