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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?.
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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
Small Populations: Drifts occur more easily Limit mating choices Large Populations: Likely to remain more stable. V. Results:
Summary: • Natural Selection acts in populations • overproduction, genetic variation, adaptations, selection • Forces effect Variation • Gene Flow, Nonrandom Mating, Drift, Mutation • Changes may occur in the population • Scientists measure the changes