How do we know if a population is evolving?

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Presentation transcript:

How do we know if a population is evolving?

When is a population not evolving? How do we know if a gene pool has changed? The Hardy-Weinberg Principle can help answer these questions.

The Hardy-Weinberg Principle states: Genetic equilibrium will be reached if the frequency of alleles remains stable generation after generation. Genetic equilibrium = no evolution occurring.

Hardy-Weinberg Principle Conditions necessary for genetic equilibrium are: No mutation occurs Immigration and emigration do not occur (population is isolated from other populations) - no gene flow. Population is very large Mating is totally random All individuals survive and reproduce equally (no natural selection)

Hardy-Weinberg Principle It is virtually impossible to meet these conditions. Allelic frequencies do change in populations, therefore evolution occurs. The main application of this principle is calculating allele and genotype frequencies in a population.

In a population, the sum frequency of alleles will equal 1. This can be expressed as: p + q = 1 Where: p = frequency of the dominant allele q = frequency of recessive allele

Hardy-Weinberg Equation p2 + 2pq + q2 = 1 Where: p2 = frequency of individuals homozygous for the dominant allele 2pq = frequency of heterozygous individuals q2 = frequency of individuals homozygous for the recessive allele