30 March Pop_Genetics.ppt1 Population Genetics Selection at the genetic level

30 March Pop_Genetics.ppt2 Observations Diversity Adaptation Variation High reproductive rates = overproduction “struggle for existence”

30 March Pop_Genetics.ppt3 Variation Darwin did not know what causes variation. Experiments with plants  3:1 phenotypic ratio, but Darwin couldn’t/didn’t apply correct math. Mendel published on peas (1866) Copy of Mendel’s paper found in Darwin’s library years after his death. Darwin did read German; but... No evidence Darwin ever read Mendel’s paper, or understood it

30 March Pop_Genetics.ppt4 Variation Mendel’s genetics rediscovered, 1900 Correns, Tschermak, DeVries Years of dispute over cause of evolution Natural selection vs. genetics “Modern Synthesis” 1930’s Genetics and natural selection reconciled

30 March Pop_Genetics.ppt5 Variation Sources of variation Point mutation: Change in one base pair in DNA directs production of modified protein, or no product

30 March Pop_Genetics.ppt6 Variation Sources of variation Chromosomal mutation (mice on Madeira) Rearrangement of genes (loci) on chromosomes Alters expression of some genes Gene duplication

30 March Pop_Genetics.ppt7 Variation Sources of variation Sex and Recombination Crossing-over, independent assortment, fertilization Alters expression Produces new combinations in genotypes Produces new combinations of phenotypes

30 March Pop_Genetics.ppt8 Population Genetics Essential concept: Gene pool “Collection” of all alleles of all individuals in a population Within a gene pool, alleles have frequencies Allele frequency = proportion of an allele among all alleles of a given gene.

30 March Pop_Genetics.ppt9 Population Genetics Gene pool Allele frequency = proportion of an allele among all alleles of a given gene. In population of 500, = 1000 alleles at “eye color” locus 700/1000 are “red” »f(A) 70%, or f(A) 0.70 = p 300/1000 are “sepia” »f(a) 30%, or f(a) 0.30 = q

30 March Pop_Genetics.ppt10 Population Genetics If we know allele frequencies, we can calculate genotypic and phenotypic frequencies.

30 March Pop_Genetics.ppt11 Population Genetics Appears that recessive allele/phenotype is disappearing! Puzzled early geneticists ~ Have allele frequencies changed? NO Change !

30 March Pop_Genetics.ppt12 Population Genetics Hardy-Weinberg Principle/equilibrium G. H. Hardy ( ) English mathematician Wilhelm Weinberg ( ) German physician & geneticist

30 March Pop_Genetics.ppt13 Population Genetics Hardy-Weinberg Principle/equilibrium Allele frequencies remain unchanged generation to generation

30 March Pop_Genetics.ppt14 Population Genetics Hardy-Weinberg Principle/equilibrium Mathematical model Assumptions/conditions Large population Random interbreeding No selection No mutation No gene flow (migration among populations)

30 March Pop_Genetics.ppt15 Population Genetics Violation of Hardy-Weinberg equilibrium Small, NOT Large, population “Genetic drift”

30 March Pop_Genetics.ppt16 Population Genetics Violation of Hardy- Weinberg equilibrium Small population “Bottleneck” effect Founder effect

30 March Pop_Genetics.ppt17 Population Genetics Violations of Hardy-Weinberg equilibrium  NON-Random breeding Sexual selection & female choice  Pea-fowl Male dominance, combat  Big-horn sheep

Population Genetics Violations of Hardy-Weinberg equilibrium Mutation Introduces/ adds new alleles 30 March Pop_Genetics.ppt18

30 March Pop_Genetics.ppt19 Population Genetics Violations of Hardy- Weinberg equilibrium Gene flow Migration among populations; Interbreeding with members of other populations.

30 March Pop_Genetics.ppt20 Population Genetics Violations of Hardy-Weinberg equilibrium Gene flow (migration among populations) Movement of pollen from one population to another

30 March Pop_Genetics.ppt21 Population Genetics Violations of Hardy-Weinberg equilibrium Movement of pollen from one population to another

Population Genetics 30 March Pop_Genetics.ppt22 Violations of Hardy- Weinberg equilibrium YES, selection Relative fitness Balancing selection, “heterozygote advantage” Frequency-dependent selection

30 March Pop_Genetics.ppt23 Evolution & Population Genetics Limitations of evolution Selection can only act on existing variations. Genes, alleles, phenotypes (anatomy and physiology) are limited by historical & developmental constraints. Adaptations are compromises. Better adaptations can be imagined, designed by engineers, but the genes or alleles don’t exist. Chance, natural selection, and environment interact.