Chapter 16 Population Genetics and Speciation

Objectives CLE Explain how genetic variation in a population and changing environmental conditions are associated with adaptation and the emergence of new species. CLE Explain how genetic variation in a population and changing environmental conditions are associated with adaptation and the emergence of new species.

Darwin’s Finches

Five conditions under which evolution may take place Genetic mutations Genetic mutations Gene flow Gene flow Genetic drift Genetic drift Nonrandom mating Nonrandom mating Natural selection. Natural selection.

Mutation Mutations are changes in the DNA. Mutations are changes in the DNA.

Gene Flow Emigration and immigration cause gene flow between populations and can thus affect gene frequencies. Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.

Genetic Drift Genetic drift is a change in allele frequencies due to random events. Genetic drift is a change in allele frequencies due to random events. Genetic drift operates most strongly in small populations. Genetic drift operates most strongly in small populations.

Nonrandom Mating Mating is nonrandom whenever individuals may choose partners. Mating is nonrandom whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual’s success at mating. Sexual selection occurs when certain traits increase an individual’s success at mating. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual.

Natural Selection Three general patterns Three general patterns Stabilizing Selection Stabilizing Selection favors the formation of average traits. favors the formation of average traits. Disruptive Selection Disruptive Selection favors extreme traits rather than average traits. favors extreme traits rather than average traits. Directional Selection Directional Selection favors the formation of more-extreme traits. favors the formation of more-extreme traits.

The Concept of Species Biological species concept Biological species concept a species is a population of organisms that can successfully interbreed but cannot breed with other groups a species is a population of organisms that can successfully interbreed but cannot breed with other groups

Isolation and Speciation Geographic Isolation Geographic Isolation Results from the separation of population subgroups by geographic barriers. Results from the separation of population subgroups by geographic barriers. Allopatric Speciation Allopatric Speciation Speciation due to separation of subgroups of a population Speciation due to separation of subgroups of a population Reproductive Isolation Reproductive Isolation Results from the separation of population subgroups by barriers to successful breeding. Results from the separation of population subgroups by barriers to successful breeding. Sympatric Speciation Sympatric Speciation Reproductive isolation within the same geographic area Reproductive isolation within the same geographic area

Allopatry vs Sympatry

Reproductive isolation: Monkeyflower

Reproductive isolation

Rates of Speciation Gradualism Gradualism species undergo small changes at a constant rate. species undergo small changes at a constant rate. Punctuated equilibrium Punctuated equilibrium new species arise abruptly, differ greatly from their ancestors, and then change little over long periods. new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.

Variation of Traits Within a Population Variations in genotype arise by mutation, recombination, and the random pairing of gametes. Variations in genotype arise by mutation, recombination, and the random pairing of gametes.

The Gene Pool The total genetic information available in a population is called the gene pool. The total genetic information available in a population is called the gene pool. Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population Predicting Phenotype Predicting Phenotype Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population. Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population.

The Hardy-Weinberg Genetic Equilibrium Allele frequencies in the gene pool do not change unless acted upon by certain forces. Allele frequencies in the gene pool do not change unless acted upon by certain forces. Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable. Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable.

Phenotype Frequency

Calculating using the Hardy Weinberg equation Dominant allele frequency = p Dominant allele frequency = p Recessive allele frequency = q Recessive allele frequency = q p + q = 1 p + q = 1 p 2 +2pq+ q 2 = 1 p 2 +2pq+ q 2 = 1