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Download Mechanisms of Evolution
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The Genetic Basis of Evolution Gene Pools are all of the alleles (alternate forms of genes) in all of the individuals that make up a population. What Drives Evolution? There are 5 forces of change. Recombination 1. Mutations One type of mutation at the level of the gene. One type of mutation at the level of the chromosome. Mutations -occur randomly - can be beneficial, neutral, or harmful in their effects Venom-like proteins first appeared about 200 million years ago 2. Gene Flow or Migration • is the transfer of alleles or genes from one population to another. • This makes separate populations more similar genetically. Ex. Gene flow in plants – wind-dispersed pollen Gene Flow or Migration 3. GENETIC DRIFT • A change in the population because of a random event, such as a catastrophe • The smaller the population, the less genetic variety it has. • 2 Types: a. Genetic Bottleneck – allele frequency is altered due to a population crash. -Catastrophe -Only the survivors will reproduce offspring . b. The Founder Effect • occurs when a small number of individuals from one population found a new population that is reproductively isolated from the original one. Endangered Species Are in the Narrow Portion of a Genetic Bottleneck and Have Reduced Genetic Variation 4. Natural Selection Natural selection leads to adaptation – an increase in the fitness of a population in a particular environment. • Successful (adaptive) genotypes become more common in subsequent generations, • causing an alteration in allele frequency over time • leads to a consequent increase in fitness. • The production of healthy, fertile offspring results in VARIATIONS in the gene pool. . Darwin’s Finches and the Theory of Evolution of Natural Selection Case Study 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. 5. Recombination -Genetic material combined during sexual intercourse -Crossing over -Enormous diversity in species -recombination or shuffling of genes -creates new allele combinations in the gametes (sex cells) Crossing Over Chromosomes