Chapter 17.1+2 State Standard: 8a. Students know how natural selection determines the differential survival of groups of organisms. Objectives: How does natural selection determine the survival of groups of organisms? What are the mechanisms that change population genetics over time?

I. Population Genetics Studying microevolution by observing changes in the numbers and types of alleles in populations. Microevolution is the change of inherited traits in a population over time. Explained: We are looking at the changes in genetic variation in a given population.

I. Population Genetics Scientists study polygenic phenotypes by measuring each individual in the population and then analyzing the distribution of those measurements. Distribution is an overview of frequency and range of values. “Hill” or “Bell” shaped curves show normal distribution. “Normal height” would fall in the center of the hill.

II. Sources of Genetic Variation: Genetic Variation is all of the available alleles in a gene pool. The number one source of new alleles in a population is: Mutation!! Caused by: 1. Nature 2. Exposure to mutagens

III. Measuring Variation and Change Scientists record the frequency of alleles in the gene pool of a population. Frequency – a ratio of a group that is of one type. Scientists gather and analyze data on a specific trait, measuring each individual in a population.

III. Measuring Variation and Change Changes can be measured in: genotype frequency (RR, Rr, rr) OR allele frequency (R or r) Populations in which no change has occurred between generations is considered to be in a state of genetic equilibrium. Hardy-Weinberg Principle states that a population will not change unless one of 5 forces acts upon it.

IV. Forces of Genetic Change Gene Flow – genes are added or removed from the population (migration) Immigration – Into the group Emmigration – exit the group Nonrandom Mating – limits in the choice of mates Limited genotypes can change population Examples: Mating behaviors and inbreeding

IV. Forces of Genetic Change Genetic Drift – random or chance events Fire or flood kills many, leaving few alleles 4. Mutation – can add alleles 5. Natural Selection – Survival of Fittest Can eliminate certain traits

V. Results: Small Populations: Large Populations: Drifts occur more easily Limit mating choices Large Populations: Likely to remain more stable.

Summary: Natural Selection acts in populations Forces effect Variation overproduction, genetic variation, adaptations, selection Forces effect Variation Gene Flow, Nonrandom Mating, Drift, Mutation Changes may occur in the population Scientists measure the changes