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Date Created: 04/27/14
Mutation and drift Tuesolay April 22 ZQJ14 3 1 PM Chapter 264 Genetic Drift 0 Genetic drift any change in allele frequencies in a population due to chance 0 Sampling error allele frequencies of a sample does not represent that of the population Simulation Studies of Genetic Drift Computer Simulations I Simulations allow for theoretical evolution for many generations I Demonstrates the differences between the effects of drift in small vs large populations I Shows the consequences for genetic variation when alleles drift to fixation or loss Key Points About Genetic Drift I Random w respect to fitness I Most pronounced in small populations I Can lead to random loss or fixation of alleles Experimental Studies of Genetic Drift 0 Genetic marker specific allele that causes a distinctive phenotype 0 Kerr and Wright experiment I 96 small population consisting of four adult female and four adult male flies I After the first generation breed they chose 4 males4 females from each group and allowed them to breed I Repeated this for 16 generations I Results demonstrated that both lose and fixation of alleles occurred What Causes Genetic Drift in Natural Populations Founder Effects on the Green Iguanas of Anguilla I Founder event occurs when group immigrates to a new region and creates a new population I Founder effect change in allele frequencies that occurs in founder event I Example New population of green iguanas on Anguilla III Unlikely that allele frequencies matched source population Genetic Bottleneck on Pingelap Atoll I Genetic bottleneck sudden reduction in of alleles in population I Example Typhoon and famine in South Pacific kills all but 20 people and about one individual caries the CNGB3 allele that codes for serious vision deficiency Chapter 266 Mutation 0 Independent assortment and recombination create new combinations of existing genes 0 Point mutations change in nucleotide sequence 0 Chromosomelevel mutation typically duplication that increases the of copies of a gene 0 Lateral gene transfer horizontal gene transfer transfer of genes from one species to another 0 Mutation increases diversity but aee39s impact on fitness is random 0 A beneficial allele will increase in frequency in a population due to natural selection Mutation as an Evolutionary Process 0 Mutation is not a significant mechanism of evolutionary change in eukaryotes 0 Mutation is significant in bacteria and archaea which have short generation times 0 Mutation is slow compared to selection genetic drift and gene flow Experimental Studies of Mutation Experimental Evolution I Richard Lenski grew bacteria from one single cell froze them at regular intervals then compared future generations w older generations Biology 180 Page 1 I More recent generations outnumbered older generations due to mutation Fitness Increased in Fits and Starts I Relative fitness increased 30 over time in sequential sudden bursts I Stairstep pattern Beneficial mutation grew rapidly in a population then no mutations for several generations Studies of Mutation in Natural Populations 0 Mutation natural selection can produce polymorphisms color variations Lateral Gene Transfer I Pea aphids typically produce carotenoids that gives them their green or red color I No other animals can produce carotenoids therefore the genes likely came through gene transfer from a fungal symbiont Gene Duplication I Two types of enzymes responsible for biosynthesis of carotenoids I In red pea aphids there are three enzymes that synthesize yellow green and red carotenoid pigments I Three enzymes are the result of duplication then point mutations Take Home Messages 0 Mutation is ultimate source of genetic variation o Evolution would stop without mutation 0 Mutation alone does not change allele frequencies at a particular gene greatly Biology 180 Page 2
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