Population Genetics Population: a group of organisms of the same species living together in a given region and interbreeding. Allele: Different forms of a gene for a trait. Gene pool: the total of alleles present in a population

Sources of variation in a population Mutations. Genetic recombination (sexual reproduction) Migration (Founder effect: new colony founded by only a few individuals) Genetic drift (changes in a population’s genes that are happening randomly) Speciation (formation of new species)

Hardy-Weinberg Law The frequency of genes leading to a certain characteristic in a population does not change unless evolutionary forces act on the population. No mutation No natural selection Random mating Big population (no inbreeding) No migration in or out of the population.

Evolution of species (speciation) Divergent evolution: species become different over a long period of time. Adaptative radiation (species spread out to new territories). Convergent evolution: Different species undergoing similar adaptations and evolving more alike Coevolution: two species evolve together, as they depend on each other Extinction: Species disappear. Gradualism: slow, gradual and even evolution. Punctuated Equilibrium: no changes, punctuated with bursts of sudden evolution

Mechanisms of speciation Allopatric speciation: A geographical process splits or fragments a population such that the groups evolve separately and cannot interbreed. Continental drift. Sympatric speciation Mostly in plants Hybridization Polyploidy Autopolyploidy Allopolyploidy

Isolating mechanisms Prezygotic barriers Postzygotic barriers Ecological barriers Behavioral barriers Mechanical barriers Gametic barriers Postzygotic barriers Hybrid inviability Hybrid breakdown Hybrid sterility

Adaptations: Camouflage

More camouflage

Adaptations: Warning coloration

Adaptations: Seasonal changes

Adaptations: Mimicry

Types of Natural Selection Directional selection Stabilizing selection Disruptive selection

Hybrid animals