EVOLUTION HOW GENOTYPES AND PHENOTYPES CHANGE OVER TIME Genetic Variation Population Genetics The study of patterns of genetic variation A species of organisms capable of interbreeding Collection of all alleles present in all individuals Species Gene pool in a species Populations Interbreeding groups of organisms of the same species living in the same geographical area What can cause genetic variation Mutation Somatic Germ line Mutations can be Deleterious Neutral Advantageous Recombination Measuring Genetic Variation Allele Frequencies Allele Frequency of copies of an allele total of alleles in population Example 1 The genotypes for pea color in Mendel s pea plants What are the frequencies of the a and A alleles if every plant is AA yellow pea plant Aa yellow pea plant aa green pea plant green Allele Frequencies Allele Frequency of copies of an allele total of alleles in population Example 2 A population of 100 pea plants has the following genotype frequencies 50 aa 25 Aa 25 AA What is the frequency of a Measuring Genotype Allele Frequencies Observable traits Gel electrophoresis DNA sequencing Observable Traits Gel Electrophoresis DNA Sequencing Uses gel electrophoresis to determine the exact sequence of the gene Example observe differences in the alcohol dehydrogenase ADH gene in 50 fruit flies In sequencing the gene we find 70 that have an A and 30 that have a G at a given position in the gene Allele frequency for A 70 100 or 70 Allele frequency for G 30 100 or 30 Evolution A change in allele or genotype frequency in a population over time Example Generation 1 of a population has 200 copies of the blue eye allele Generation 2 of the population of the same size has 300 copies of the same allele More basically it is a change in the genetic makeup of a population over time POPULATIONS EVOLVE NOT INDIVIDUALS Hardy Weinberg Conditions There can be no differences in the survival and reproductive success of individuals Populations must not be added to or subtracted from by migration There can be no mutation The population must be sufficiently large to prevent sampling errors Individuals must mate at random Hardy Weinberg Relation Natural Selection Darwin s Findings Published in 1859 in On the Origin of Species Suggested natural selection brings about adaptation Species are not unchanging they have evolved over time Organisms adapt to their environment Work of Thomas Malthus Essay on the Principle of Population Populations have the potential to increase exponentially but does not occur Limited resources Fitness Which individuals will win the competition Types of Selection Natural selection that increases the frequency of favorable allele Natural selection that decreases the frequency of a harmful Positive Negative allele Balancing Natural selection that maintains an allele at some intermediate frequency between 0 and 100 Acts to maintain two or more alleles in a population Heterozygote advantage Heterozygote Advantage Patterns of Natural Selection Sexual Selection Other Factors Causing Changes in Allele Frequencies Movement of individuals from one population to Migration another Called Gene flow Mutation most common cause of changes Genetic Drift Random change in allele frequencies from generation to generation Bottleneck Founder event Genetic Drift Molecular Evolution Molecular Clock Stabilizing Selection Artificial Selection
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