Genetic Equilibrium

Chapter 16- Section 1

What is a population?A group of individuals of the same species that routinely interbreed

Population Genetics – the study of evolution from a genetic point of view

Microevolution- the change in the collective genetic material of a population

Biston betularia f. typica is the white-bodied form of the peppered moth

Biston betularia f. carbonaria is the black-bodied form of the peppered moth.

Variation of Traits within a population

Within a population, individuals will vary in observable traits

Ex. Fish of a single species in a pond will vary in size

Few fish are very short or very long

Causes of variationVariations influenced by environmental factors

Ex. Amount or quality of food, sunlight, living space

Variations in genotype1. Mutation – a random change in a gene2. Recombination – reshuffling of genes in a diploid3. Random pairing of gametes – millions of sperm are produced, 1 gets to fuse with egg

The Gene PoolA population’s gene poolgene pool is the total of all genes in the population at any one time.

• If all members of a population are homozygous for a particular allele, then the allele is fixed in the gene pool.

The Hardy-Weinberg The Hardy-Weinberg TheoremTheoremUsed to describe a non-evolving populationnon-evolving population..

Natural populations are NOT expected to actually be in Hardy-Weinberg equilibrium

Deviation from Hardy-Weinberg equilibrium results in evolution

Understanding a non-evolving population, helps us to understand how evolution occurs

*Genotype frequencies in a population tend to remain the same from generation to generation unless acted on by an outside source

Conditions of the H-W Conditions of the H-W TheoremTheorem

1.Large population size - small populations can have chance fluctuations in allele frequencies (e.g., fire, storm).

2.No migration- immigrants can change the frequency of an allele by bringing in new alleles to a population.

3.No net mutations- if alleles change from one to another, this will change the frequency of those alleles

Conditions of the H-W Conditions of the H-W TheoremTheorem

3.Random mating- if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.

4.No natural selection- if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

•Hardy-Weinberg Equilibrium                                   The gene pool of a non-evolving population remains constant over multiple generations; i.e., the allele frequency does not change over generations of time. •The Hardy-Weinberg Equation:                                     1.0 = p2 + 2pq + q2

                                                where p2 = frequency of AA genotype; 2pq = frequency of Aa plus aA genotype; q2 = frequency of aa genotype

Hardy-Weinberg Equilibrium

Population of cats n=10016 white and 84 blackbb = whiteB_ = black

Can we figure out the Allele frequencies of individuals BB and Bb?