Population Genetics Biological Anthropology Population A potentially interbreeding

Population Genetics Biological Anthropology

Population • A (potentially) interbreeding group of organisms • (usually) a subset of a species

“Populations” Differ

How Should We Describe Populations? Monogenic Traits Polygenic Traits • Qualitative • Quantitative • Discontinuous graph • Continuous graph

Use Polygenic Traits? • Advantage: often easily observable • Disadvantage: can change over an individual’s life time • Poorly suited for population studies

Racism • A social/cultural phenomenon • Attempts to distinguish between human populations on the basis of polygenic traits • Used to justify hierarchies within society • Is not based on scientifically valid criteria

Use Monogenic Traits! • Disadvantage: not always easily observable • Advantage: do not change over an individual’s life time • Useful in the study of populations • Genetic Markers = monogenic traits in which the genotype is known

Genetic polymorphism When two or more phenotypes exist within a population that means that the population exhibits variation for that trait and variation is what makes evolution possible

Adaptation a trait that increases an organism’s reproductive success What adaptation is being measured here? How might this adaptation increase an individual’s reproductive success?

Adaptation (a classic example) The wing color of the Peppered Moth is a monogenic trait

Adaptation produced by natural selection in the context of a particular environment A light variant mating with a dark variant Light and dark variants on light and dark backgrounds

Adaptation produced by natural selection in the context of a particular environment Smokestacks during the Industrial Revolution

Evolution defined drum roll please… A change in allele frequency from one generation to another

This means that… the unit of selection is the individual while the unit of evolution is the population

Population Genetics • Studies how evolution occurs in populations of organisms • Population – a (geographically localized) group of individuals in a species that share a common gene pool and tend to find their mates within this group

Let’s run away! (and establish a population) Fabulous Baker Island

What are the factors that could influence the evolution of our population? • Founder’s effect • Natural selection • Mutation • Migration • Assortative mating – Positive – negative • Genetic drift

Founder’s effect • How well would we represent the population from which we are derived? • So. Cal!

Natural Selection • Do blondes have more fun (and more early onset skin cancer)? • Is it better to be redder? • Hereditary diseases, anyone? • Other possibilities?

Mutation • Random mutations • Heightened mutation rates? • Cosmic rays? Uranium ore

Migration • Do some people leave? • Do others arrive? • Did some “visit”? • Gene flow vs. migration Hypothesized migration pattern of the Pacific Islands

Assortative Mating Positive Assortative Mating Negative Assortative Mating • phenotypically similar organisms • phenotypically dissimilar organisms • increases homozygosity • increases heterozygosity • decreases variation • increases variation