Evolution of Populations Marie Černá
Microevolution Genetic drift in small population Gene flow by migration Mutation Nonrandom mating Natural selection
Genetic Drift
Genetic Drift - small populations
Genetic Drift - large populations
Genetic Drift - Bottle neck effect
northern elephant seals of the coast of Mexico During the 1890’s, their population was reduced due to hunting to about 20 individuals. (It is also likely that one male would have fathered the offspring of the entire group.)
Genetic Drift - Founder principle Drosophila subobscura (fruit fly) European → American
Genetic Drift - Founder principle
Gene flow - migration
Mutation
Nonrandom mating inbreeding assortative mating
Natural selection the differential ability to survive and produce viable, fertile offspring is likely to adapt a population to its environment (accumulates and maintains favorable genotypes)
Genetic variation: the substrate for natural selection within populations (polymorphism) between populations (geographical variation)
Polymorphism
Geographic variation
Geographic variation - Cline
Sources of Genetic variation Mutation (affection of function) Sexual recombination
Crossing over in meiosis
Independent assortment
Preservation of Genetic variation Diploidy (heterozygote protection) Balanced polymorphism
Heterozygote advantage
Frequency-dependent selection
Modes of natural selection
Directional selection is most common - during periods of environmental change - when members of a population migrate to some new habitat with different environmental conditions
Directional selection peccaries Desert cactus population
Diversifying selection
a species of finch lives in Cameroon, West Africa small-billed birds (soft seeds) large-billed birds (hard seeds)
Stabilizing selection This mode of selection reduces variation and maintains the status quo for a particular phenotypic character. It keeps the majority of human birth weights In the 3 – 4 kg range. For babies much smaller or larger than this, infant mortality is greater.
Stabilizing selection Desert cactus population
Literature Biology, eighth edition, Campbell, Reece Unit four: Mechanisms of Evolution Chapter 23: The Evolution of Populations Pages 468 – 486