BIOL 1108 1st Edition Lecture 1 Outline of Current Lecture I Evolution II Mechanisms of evolution III Natural Selection a Examples explanations and definition IV Migration gene flow a Examples explanations and definition V Genetic Drif a Examples explanations and definition VI Mutation a Examples explanations and definition Current Lecture I Evolution Evolution 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 survive Answer F Definition 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 populations III 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 environment Definition Natural Selection nonrandom survival and reproduction of phenotypes or genotypes A nonrandom correlation between phenotype or genotype and fitness IV Migration gene flow Suppose you have individuals that migrate from one population to another What will happen over time Freq A 0 7 Freq a 0 3 Population 1 Freq A 0 5 Freq a 0 5 Population 2 V 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 low levels 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 allele A a is the mutation rate per allele locus per generation