BIOL 1108 1st Edition Lecture 1 Outline of Current LectureI. EvolutionII. Mechanisms of evolutionIII. Natural Selectiona. Examples, explanations, and definition IV. Migration (gene flow)a. Examples, explanations, and definition V. Genetic Drifa. Examples, explanations, and definition VI. Mutation a. Examples, explanations, and definition Current LectureI. EvolutionEvolution has occurred when… a) Offspring have a different phenotype than the b) parents c) Individuals change over time d) Mutations change base sequences in alleles e) The allele frequencies change in a population f) A population has a different allele frequency in this generation compared to the last generation g) A species needed to change to surviveAnswer: FDefinition: A change in the frequency of an allele (e.g. an allele for beak depth) between generations is the basic definition of evolution.II. Mechanisms• Natural selection (constant selection) Causes non-random changes in allele frequencies Tends to reduce variation• Migration (gene flow) Homogenizes populations• Mutation Introduces variation Does not cause signify changes in allele frequencies• Genetic drif Causes random changes in allele frequencies Leads to loss of variation within a population More important in small populationsIII. Natural Selection • Populations show heritable variation for numerous characters (heritability ≠ 0).• Populations have a huge capacity for increase, but tend to remain approximately constant in size, implying high mortality.• Particular phenotypes in a given environment increase the likelihood that certain individuals contribute to the next generation.• Unequal contribution of different phenotypes, with heritability, causes a population to change.• Fitness: refers to how well an individual survives (viability) and how many offspring it produces (reproduction)• Fitness is the quantity that we use to measure the impact of selection• Adaptation: refers to any (biological) trait that increases fitness relative to individuals without the trait, in a particular environmentDefinition:Natural Selection: nonrandom survival and reproduction of phenotypes or genotypes• A nonrandom correlation between phenotype (or genotype) and fitnessIV. Migration (gene flow) • Suppose you have individuals that migrate from one population to another• What will happen over time?Population 1 Population 2Freq(A) = 0.5Freq(a) = 0.5Freq(A) = 0.7Freq(a) = 0.3V. Genetic Drif• Random Changes in allele frequencies Independent of phenotype (and genotype)• Founder effect Some populations are started (founded) by only one or a few individuals These populations are subject to drif early, and ofen show low variation and high frequencies of a few rare disorders• Bottleneck effect Some large populations historically went through a bottleneck, due to disease for example.  Bottlenecked populations will be subject to drif while small, and will show relatively lowlevels of variation given their size Examples Cheetahs (bottleneck in last 20,000 years). No variation! Elephant seals (bottleneck to 20 individuals in 1890, now number 30,000). No variation! Eastern European Jews (Ashkenazi). Reduced variation.VI. Mutation• A mutation changes the DNA sequence at a locus into another sequence• A mutation leads to a change in alleleA a µ• µ is the mutation rate per allele (locus) per