Population and Speciation Population Genetics: The study of Evolution from a genetic point of view.
Variations of Traits • Biologists measure traits in large samples when studying variation. • Bell curves show that average populations have similar traits. A few display the extremes of a trait. • Varying genotypes arise in 3 ways • Mutations from flawed copies of genes • Recombination from an independent assortment of genes during meiosis • Random fusion of gametes, combination of one sperm and one egg.
Allele Frequency and the Gene Pool • Gene pool: the total genetic information available to a population • Allele frequency: determined by dividing the number of a certain allele by the total number of alleles of all types in a population. • Phenotype frequency: The number of individuals with a certain phenotype divided by the total number of individuals in a population.
Harvey-Weinberg Genetic Equilibriumbased on an ideal hypothetical population not evolving- This is not real life • 1. no net mutations occur • 2. individuals neither enter or leave a population • 3. The population is large • 4. individuals mate randomly • 5. Selection does not occur
Requirements for Genetic Equilibrium.Mutation: • Mutation: spontaneous mutation is slow over a longer period of time • Mutagens force mutations from chemical or radiation exposure • They produce new alleles that may be harmful or beneficial to a population
Migration • Immigration: the movement into a population • Emigration: the movement out of a population • Gene Flow: the process of genes moving from one population to another.
Genetic Drift • The phenomenon by which allele frequencies in a population change as a result of random events or chance. • Small populations experience a large amount of drift, they lose genetic diversity • Large populations maintain a small amount of genetic drift
Nonrandom Mating • Random mating doesn’t always occur in a population because of geographic proximity • Nonrandom mating is selection which may result in genes being to similar, which cause genetic disorders in a population • Selection of a mate based on similar characteristics is assortative mating
Natural Selection • Members of a species more likely to pass on their genes to the next generation • Stabilization selection: individuals with average form of a trait have the highest fitness • Directional selection: individuals that have a more extreme form of a trait have a greater fitness than those with average form of a trait. • Disruptive selection: individuals with extreme variation have greater fitness than the average form of a trait. • Sexual selection: Males must be selected by females based on traits that are desired. The genes of successful reproducers not just survivors are amplified through natural selection.
Concept of Species • Speciation: Some species are very similar to their ancestral species while other populations become quite different • Morphology: the internal and external structure and appearance of an organism • Biological species concept: a species is a population of organisms that can successfully interbreed but can not breed with other groups.
Isolating Mechanisms • Geographic isolation: physical separation • Reproductive isolation: barriers to successful breeding between groups in the same area. • Broad type: prezygotic-before fertilization and postzygotic-after fertilization
Rates of Speciation • Speciation may take millions of years, some may occur more rapidly, it may not occur smoothly and gradually. • Punctuated equilibrium: a sudden shift in form that is often seen in the fossil record.