Hardy-Weinberg Genetic Equilibrium Flamingo population

Remember: to maintain 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 occur, they can cause the gene frequency to change in a population. If any of the 5 factors 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.

Mutations Mutations occur normally but at extremely low rates. Mutations occur normally but at extremely low rates. Mutations do not cause gene frequencies to change. Mutations do not cause gene frequencies to change.

Migration Immigration (movement in) or emigration (movement out) can effect gene frequencies. Immigration (movement in) or emigration (movement out) can effect gene frequencies. Movement of individuals from one population to another results in gene flow. Movement of individuals from one population to another results in gene flow.

Genetic Drift Small populations are subject to genetic drift. Small populations are subject to genetic drift. Random events lead to changes in gene frequencies. Random events lead to changes in gene frequencies. Each line represents a different population. Each starts with the same number of allele A. over time the number of individuals with that allele changes. If a population is small enough over several generation the allele will either be 0 or 100% present.

Nonrandom Mating Random mating throughout a population does not occur. Random mating throughout a population does not occur. – Geographical regions. – Sexual selection Ex: birds of paradise Ex: birds of paradise – Assortive mating Ex: Fruit flies. Ex: Fruit flies.

Directional Selection Cactus and wild pigs Wild pigs impose selection upon the cactus population. Wild pigs impose selection upon the cactus population. – Cactus that have fewer needles do not survive to reproduce. – Cactus with more needles survive to reproduce.

Result of directional selection is a shift in the population towards more spines. Result of directional selection is a shift in the population towards more spines. One extreme is selected for and one against. One extreme is selected for and one against. Ex: cliff swallows after a cold snap. Ex: cliff swallows after a cold snap. Directional Selection results I’ve posted a short article on how cliff swallow wing length has shorted due to new selective pressures. Read it and refer to it in your summary.

Both extremes are selected against. Both extremes are selected against. The average is selected for. The average is selected for. Population becomes more similar due to average being selected for. Population becomes more similar due to average being selected for. Ex: human birth weight Ex: human birth weight Stabilizing Selection

Extremes are selected for. Extremes are selected for. Results in two distinctly different populations. Results in two distinctly different populations. Disruptive selection can lead to two species. Disruptive selection can lead to two species. Average is selected against. Average is selected against. Ex: finches in west Africa, eat different sized seeds. Ex: finches in west Africa, eat different sized seeds. Disruptive Selection

Calculating allele frequencies Use the Hardy-Weinberg equation: – p² + 2pq + q² = 1 –“q” is the recessive trait and q² is homozygous recessive – “p” is the dominate trait and p² is homozygous dominant. –pq is heterozygous – added together you have 100% of the individuals in a population

Disruption of Genetic Equilibrium - Summary of Selection

Summary Review 1.Describe the 3 types of selection. 2.What is genetic drift, what causes it, an what results from it? 3.What can cause new genes to enter a population? 4.What do these two pictures illustrate?