unit two: evolution of populations

Define population genetics and describe how scientists use population genetics in studying population evolution

• population genetics: processes that cause changes in allele and genotypic frequencies in population across generations

• scientists definition: how does genetic variation within organisms change over time?

Define the Hardy-Weinberg principle and discuss its importance

• allows calculation of allele and genotypic frequencies from one generation to the next

• principle: allele and genotypic frequencies stay constant from generation to generation because of the absence of evolutionary influences

Describe the different types of variation in a population

• phenotypic variation: diversity in traits

• genetic variation: diversity of alleles and genotypes

Explain why heritable variation is necessary for evolution by natural selection

• heritable variation: traits that can be passed down from parent to offspring through genes

• non-heritable variation: differences in traits that CANNOT BE PASSED DOWN and are caused by external factors

Describe genetic drift and the bottleneck effect

genetic drift

• random change in allele frequencies from one generation to the next.

• decreases variation within a population, increases among populations

bottleneck effect

• when populations are reduced near extinction

Explain how each evolutionary force can influence a population's allele frequencies

directional selection: reduces the abundance of the other genotypes

stabilizing selection: favors the most common phenotype (heterozygous); further reduces the other phenotypes

disruptive selection: favoring phenotypes on either extremes

Explain the different ways natural selection can shape populations

• directional selection: trait value SHIFTS (you’re new flop era)

• disruptive selection: favors the two extremes (mid is bad)

• stabilizing selection: favors the average traits (mid is good!)

Describe how different selective forces can lead to different outcomes in terms of population variation

• random genetic drift: DECREASES within populations, INCREASES among populations

• migration: INCREASES within populations, DECREASES among populations

• mutation: INCREASE or MAINTAIN

• natural selection: MAINTAIN or DECREASE

Define sexual selection and discuss how/why certain traits may evolve by sexual selection

selection on traits in males and females that increase mating success

• intrasexual selection: members of the same sex compete for mates (male against male)

• intersexual selection: members of the opposite sex choosing mates (female choosing male)