Population Genetics The science of genetic change in population. Population – all the members of a species that occupy a particular area at the same time Gene Pool – all the genes in all the members of a population

Genes and Variation Genetics Joins Evolutionary Theory Variation is the raw material for natural selection Gene pool – consists of all the genes, including all the different alleles for each gene, that are present in a population Relative frequency – the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur Therefore – evolution is any change in the relative frequency of alleles in the gene pool of a population over time 3 Sources of Genetic Variation Mutations Genetic Recombination in Sexual Reproduction (Ind assortment and crossing over) Lateral Gene Transfer (conjugation) Single-Gene (2 pheno) vs. Polygenic Traits (many pheno/bell curve) ***Natural Selection acts directly on PHENOTYPES not actual alleles*** some phenotypes are better suited to an environment than others and they will survive, reproduce and pass on their genes.

Evolution as Genetic Change in Populations How Natural Selection Works – 3 Types Stabilizing Selection Individuals with the average form of a trait have the highest fitness Represents the optimum for most traits Results in a similar morphology between most members of the species Directional Selection Individuals that display a more extreme form of a trait have greater fitness than individuals with an average form of the trait A shift in one direction Peppered moth Disruptive Selection Individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait A shift in both direction, away from the center Shell color (dark rocks and light sand)

Genetic Drift Random changes in the frequency of a gene in the absence of natural selection  occurs because of CHANCE Occurs efficiently in small populations because small changes affect more members Two examples: a. Bottleneck effect b. Founder effect

a. Bottleneck Effect Genetic drift (reduction of alleles in a population) resulting from a disaster that drastically reduces population size. Examples: 1. Earthquakes 2. Volcano’s

b. Founder Effect Genetic drift resulting from the colonization of a new location by a small number of individuals. Results in random change of the gene pool. Example: 1. Islands (first Darwin finch)

Hardy-Weinberg Principle Genetic Equilibrium – situation in which allele frequencies in the gene pool of a population remain constant The concept that the shuffling of genes that occurs during sexual reproduction, by itself, cannot change the overall genetic makeup of a population. Shows mathematically and theoretically that there are situations where evolution DOES NOT OCCUR Seldom achieved in nature

Hardy-Weinberg Principle This principle will be maintained in nature only if ALL five of the following conditions are met: 1. Very large population 2. Isolation from other populations 3. No net mutations 4. Random mating 5. No natural selection Hardy-Weinberg Principle

Species A group of populations whose individuals have the potential to interbreed and produce viable offspring.

Speciation The evolution of new species. Species that occupy an otherwise unoccupied niche face no competition, they will therefore have a 100% success rate

Reproductive Isolation Any mechanism that impedes two species from producing fertile and/or viable hybrid offspring -factor necessary for the formation of a new species. Barriers: 1. Geographic (rivers, mountains) 2. Behavorial - differences in courtship behavior 3. Temporal - fertile periods (time)

Interpretations of Speciation Two theories: 1. Gradualist Model (Neo-Darwinian): Slow changes in species overtime. 2. Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change.

Macroevolution The origin of taxonomic groups higher than the species level.

Adaptive Radiation aka Divergent Evolution Emergence of numerous species from a common ancestor introduced to new and diverse environments. Example: Darwin’s Finches

Darwin’s Finches an example of Adaptive Radiation

Convergent Evolution Species from different evolutionary branches may come to resemble one another if they live in very similar environments. Example: 1. Ostrich (Africa) and Emu (Australia). 2. Sidewinder (Mojave Desert) and Horned Viper (Middle East Desert) 3. Shark and Dolphin

Coevolution Evolutionary change, in which one species act as a selective force on a second species, inducing adaptations that in turn act as selective force on the first species. Example: 1. Acacia ants and acacia trees 2. Humming birds and plants with flowers with long tubes