Population Genetics and Evolution Population genetics: the study of properties of genes in a population. Macroevolution: change over a long period of time including evolutionary trends, new organisms penetrating new habitats, and major episodes of extinction.

Microevolution: change within populations, change in allele frequencies ( populations will gradually favor individuals with characteristics that provide an advantage, assuming the characteristics have a genetic basis- Charles Darwin.

Hardy-Weinberg Equilibrium: Evolution as changes in the frequencies of alleles in a population

Hardy-Weinberg Equilibrium Assumes five conditions are met in order to have not change in allele frequencies over time. Used as a “yard stick” to determine if evolutionary change has occurred. If one condition in not met, the result is a change in allele frequencies, therefore, evolution has taken place.

Lab 7 A and a are alleles in a population, individuals are diploid and have 2 alleles. -p is designated the frequency of “A” -q is designated the frequency of “a” p + q = 1 Diploid combinations of alleles would be AA, Aa and aa: p2 + 2pq + q2 = 1.0 “A” “Aa” “a”

The Five Conditions: The breeding population must be large. If small, Genetic Drift can occur: - Bottle neck effect -Founder effect

a. Bottleneck Effect A population is reduced due to flood, drought…where surviving individuals make new populations. Ex. Cheetahs

b. Founder Effect Few individuals disperse and become the founders of a new population. Rare alleles can be enhanced Ex. Galapagos, Hawaii

Random mating There cannot be any preferential breeding or selection of mates

3. There can be no immigration or emigration of individuals of the population.

4. There is no mutation. (random mutations are about 1 in every 100,000 cell divisions)

There is no selection Selection: The rate at which an individual leaves behind progeny that is affected by their inherited characteristics. It act directly on the phenotype because it is determined by the interaction of the genotype and the environment. Types of Selection -Natural -Artificial

Natural Selection The environment is the selection pressure (imposes conditions that determine the results of selection and effecting the direction of evolution)

Artificial Selection Desired traits are selected

Types of Selection When selective pressures select against the two extremes of a trait, the population experiences stabilizing selection. Ex. plant height might be acted on by stabilizing selection. A plant that is too short may not be able to compete with other plants for sunlight. Extremely tall plants may be more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The number of plants of medium height will increase while the numbers of short and tall plants will decrease.

In directional selection, one extreme of the trait distribution experiences selection against it. The result is that the population's trait distribution shifts toward the other extreme. In the case of such selection, the mean of the population graph shifts. Using the familiar example of giraffe necks, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks.

In disruptive selection, selection pressures act against individuals in the middle of distribution. The result is a two-peaked curve in which the two extremes of the curve create peaks. Ex. imagine a plant of extremely variable height pollinated by three different pollinators, one that was attracted to short plants, another that preferred plants of medium height and a third that visited only the tallest plants. If the pollinator that preferred plants of medium height disappeared from an area, medium height plants would be selected against and the population would tend toward both short & tall, but not medium height plants.