Population genetics

In the early 1900’s the science of population genetics was born.In the early 1900’s the science of population genetics was born. This science explained the relationship between genetics and evolutionThis science explained the relationship between genetics and evolution. Wilhelm Weinberg Population genetics

Population genetics was an important discovery because populations are the smallest unit that can evolve.Population genetics was an important discovery because populations are the smallest unit that can evolve. Traits within populations show variation.Traits within populations show variation. Genetic Equilibrium Peppered moths Think: What conditions would favor black moths over white?

Some variations are discontinuous.Some variations are discontinuous. –Ex: male Vs female –Ex: Tall pea plants Vs short pea plants. Some variations are continuous.Some variations are continuous. –Polygenic traits usually cause continuous traits –Ex: human height –Ex: human skin color –Ex: size of fish in a pond. Variation Within A Population

Continuous traits demonstrate a bell shaped curveContinuous traits demonstrate a bell shaped curve –Most individuals are in “average”. –Individuals with “extreme” variation are few in number. think: Explain the change in the graph after selection occurs. Distribution of traits

Traits are caused by:Traits are caused by: –Environment –Heredity Usually both factors play a role.Usually both factors play a role. Causes of Variation Are these plants different heights because of genetics or nutrition?

3 causes of variation in a population. 1.Mutations to DNA. 2.Independent assortment & crossing over. 3.Random fertilization. What Increases Variation?

Gene Pool;Gene Pool; –All genes found in an interbreeding population. Allele frequency;Allele frequency; –% of a particular allele in a population. Allele Frequencies In A Gene Pool

Hardy-Weinberg Genetic Equilibrium Flamingo population Allele frequencies remain the same generation after generation.Allele frequencies remain the same generation after generation. This will be true if 5 conditions are met.This will be true if 5 conditions are met.

Hardy-Weinberg Genetic Equilibrium Tule Elk population at Pt Reyes 1.No change due to mutations. 2.Individuals do not move in or out of the population. 3.The population is and remains large. 4.Random mating. 5.No selection

Disruption of Genetic Equilibrium Tule Elk population at Pt. Reyes If any of the 5 factors do not occur, they can cause the gene frequency to change in a population.If any of the 5 factors do not occur, they can cause the gene frequency to change in a population. If the gene frequencies change evolution has occurred.If the gene frequencies change evolution has occurred.

Summary review 1.What is the shape of a graph of normal distribution? 2.What is a gene pool? 3.What are 3 causes of genetic variation? 4.Given the requirements of genetic equilibrium do populations remain unchanged? Why?