Microevolution How does evolution work? Targets: Explain the significance of gene pools in understanding evolution. Tell how genetic drift, gene flow, mutation, and natural selection contribute to changes in a gene pool.

What is microevolution? 4/22/2017 What is microevolution? Microevolution is evolution on the smallest scale that cause generation-to-generation changes in allele frequency within populations. Population: a group of interbreeding organisms present in a specific location at a specific time. Allele frequency: the frequency of a particular allele in the population. Changes in allele frequency within populations drive evolution. G. Podgorski, Biol. 1010

What Drives Evolution? There are 5 forces of change. Microevolution 4/22/2017 What Drives Evolution? There are 5 forces of change. Only natural selection makes a population better adapted (more fit) to its environment. G. Podgorski, Biol. 1010

Microevolution The Genetic Basis of Evolution 4/22/2017 Gene pools are all of the alleles (alternate forms of genes) in all of the individuals that make up a population. For evolution to occur, genetic differences must at least partially account for phenotypic differences. G. Podgorski, Biol. 1010

Mutations Provide Raw Material For Evolution Microevolution 4/22/2017 Mutations Provide Raw Material For Evolution One type of mutation at the level of the gene. One type of mutation at the level of the chromosome. Mutations occur randomly and are usually neutral or harmful in their effects; only rarely are they beneficial. G. Podgorski, Biol. 1010

Gene flow is the exchange of genes with another population. Microevolution 4/22/2017 Gene Flow or Migration Gene flow is the exchange of genes with another population. This makes separate populations more similar genetically. Gene flow in plants – wind-dispersed pollen moving between Monterey pines. G. Podgorski, Biol. 1010

Gene Flow or Migration Microevolution 4/22/2017 G. Podgorski, Biol. 1010

Microevolution 4/22/2017 Genetic Drift Genetic drift is the change in the gene pool of a population due to chance. G. Podgorski, Biol. 1010

A Genetic Bottleneck is a Form of Genetic Drift Microevolution 4/22/2017 A Genetic Bottleneck is a Form of Genetic Drift In a genetic bottleneck, allele frequency is altered due to a population crash. Once again, small bottlenecked populations = big effect. G. Podgorski, Biol. 1010

Genetic Bottleneck – A Historical Case Microevolution 4/22/2017 Genetic Bottleneck – A Historical Case Note: A genetic bottleneck creates random genetic changes without regard to adaptation. A severe genetic bottleneck occurred in northern elephant seals. Other animals known to be affected by genetic bottlenecks include the cheetah and both ancient and modern human populations. G. Podgorski, Biol. 1010

Microevolution 4/22/2017 Endangered Species Are in the Narrow Portion of a Genetic Bottleneck and Have Reduced Genetic Variation G. Podgorski, Biol. 1010

The Effect of Genetic Drift is Inversely Related to Population Size Microevolution 4/22/2017 The Effect of Genetic Drift is Inversely Related to Population Size Large populations = small effects. Small populations = large effects. G. Podgorski, Biol. 1010

The Founder Effect is Another Variation of Genetic Drift Microevolution 4/22/2017 The Founder Effect is Another Variation of Genetic Drift A founder effect occurs when a small number of individuals from one population found a new population that is reproductively isolated from the original one. Migration from England G. Podgorski, Biol. 1010

The Founder Effect is Another Variation of Genetic Drift Microevolution 4/22/2017 The Founder Effect is Another Variation of Genetic Drift The South Atlantic island of Tristan da Cunha was colonized by 15 Britons in 1814, one of them carrying an allele for retinitis pigmentosum. Among their 240 descendents living on the island today, 4 are blind by the disease and 9 others are carriers. G. Podgorski, Biol. 1010

Inbreeding is preferential mating with relatives. Microevolution Non-Random Mating 4/22/2017 Non-random mating occurs when there is a bias for or against mating with related individuals. Cute, but prone to genetically-based disorders. Inbreeding is preferential mating with relatives. Inbreeding is a common form of non-random mating. Inbreeding increases the frequency of homozygous genotypes compared to random mating. This increases the frequency of recessive genetic disorders. G. Podgorski, Biol. 1010

Microevolution 4/22/2017 Natural Selection Natural selection leads to adaptation – an increase in the fitness of a population in a particular environment. Natural selection works because some genotypes are more successful in a given environment than others. Successful (adaptive) genotypes become more common in subsequent generations, causing an alteration in allele frequency over time that leads to a consequent increase in fitness. The production of healthy, fertile offspring results in changes in the gene pool. G. Podgorski, Biol. 1010

Microevolution Darwin’s Finches and the Theory of Evolution of Natural Selection Case Study 4/22/2017 Peter and Mary Grant and their colleagues observed how beak depth, a significant trait for feeding success, varied in populations experiencing climactic variations. Beak depth is a genetically determined trait. G. Podgorski, Biol. 1010