BIOL 102 Lecture Notes - Lecture 4: Allele Frequency, Gene Duplication, Genetic Variation

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Natural selection acts on individuals, but only populations evolve. Microevolution is a change in allele frequencies in a population over generations. Three mechanisms cause allele frequency change: genetic drift, gene flow, natural selection. Variation in heritable traits is a prerequisite for evolution. Mendel"s work on pea plants provided evidence of discrete heritable units (genes) Genetic variation among individuals is caused by differences in genes or other dna segments. Natural selection can only act on variation with a genetic component. Genetic variation can be measured as gene variability or nucleotide variability. Gene variability: average heterozygosity measures the average percent of loci that are heterozygous in a population. Nucleotide variability: measured by comparing the dna sequences of pairs of individuals. Nucleotide variation rarely results in phenotypic variation. Only genetically determined variation can have evolutionary consequences. New genes and alleles can arise by mutation or gene duplication. Sexual reproduction can result in genetic variation by recombining existing alleles.

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