Note for BIOL 152 with Professor Hagen at KU 2
Note for BIOL 152 with Professor Hagen at KU 2
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Date Created: 02/06/15
Evolution Genetics of Populations January 28 Biology 152 Spring 2011 f F GD 5 IMale I FFFF IE 40 I E n e an a 2 ID in t D 48 SD 51 54 56 58 ED 62 64 66 68 7D 72 74 76 78 ED 81 84 86 3 Height i nnnn s Outline Evolution within a single population Effects of mutations finish Adult lactosetolerance example Genetic variation in populations Allele and genotype frequency calculations HardyWeinberg equation Forms of natural selection Most of the human genome is NOT protein coding genes Repeated sequences 45 microsatellites tandem repeats etc Transposable elements Only 28 is transcribed into RNA Most of that consists of introns Less than 5 encodes proteins Function of noncoding sequences often not clear so effect of mutations uncertain Mutation is random Mutations do not occur because they are beneficial Nucleotides do not plan for the good of the individual Adult Lactose Tolerance Advantageous where milk is available cultural environment Northern European adult lactase persistence caused by C 9 T change within a regulatory gene East Africans G 9 C change at another location within the same gene Change is dominant activates lactase gene transcription in adult Lactose milk sugar Lactose makes up 5 of cow s milk 9 of human milk Lactose absorption After hydrolysis Lactase on surface membrane simple sugars can be absorbed Stomach Submucnss Small Intestine Large lmestine Small Intestinal Structure ENE ch or Amarmwe Cell Smnmh Muscle Cells 3mm Cell Lsdesl Csplllsrles Panelh Cans Ememendocrlne m APLlD Cell Lactose malabsorption Lactose passes on to the large intestine where it is available for fermention by bacteria Emanch 0r Alrsmmwe Cell Smnmh Mums Cells anlsl Cell Lsdesl Caplllsrles Submucuss Panelh Cans Entamendncvme Small u APUD an Intestine lmesm39le Small Intestinal Structure Can YOU drink milk a large glass without ill effects We ll use the results later a YES b NO c not sure Variation in populations terms Polymorphic locus monomorphic Gene pool a simplified MODEL of a sexually reproducing population defined as 10 Characterizing gene pools Genotype frequency Allele frequency By convention use p amp q for two allele case A population have more than two alleles 11 Calculating allele frequencies using genotype frequencies If two alleles A at frequency p a at frequency q Three genotypes AA at frequency D dominant Aa at frequency H heterozygoz e aa at frequency R recessive p D H2 qRH2 DHR1 pq1 12 AA Aa aa 8 32 10 50 individuals Count number of copies of each allele Total will be 2X number of individuals 50 individuals 9 100 total allele copies Frequency of A 2 A s from each AA homozygote 2 x 8 16 1 A from each Aa heterozygote 1 x 32 32 copies of A 48 frequency of A 48100 48 13 Allele Frequency from Genotype Frequency You can get the same result from genotype frequencies 8AA50 16D 32Aa50 64 10aa5020 R 1quot Frequency ofA 16 642 48 Frequency of a 52 I l F 14 Allele and Genotype Frequencies Table genotype AA Aa aa D H R 1 Afrequency D HI2 p a frequency H2 R q 1p 15 Predicting allele amp genotype frequencies in the next generation Simplify Gene Pool Alleles in the population Frequencies of alleles p frequency of Gametes produced CR allele 08 Each egg Each sperm gt gt q frequency of 1 80 20 80 20 CW allele 02 chance chance chance chance any lghlf EM Pearson Euucamn n p bllslina as Pearson Binary n 2 mm m Population allele frequency gamete frequency 16 PFDNT Simplifying assumptions HardyWeinberg conditions 17 Possible A Female gametes a Possible gametes Male A a AA Aa Aa aa Possible genotypes of offspring 18 Possible p gametes frequencyq Possible gametes frequency p q p2 m m 12 Possible genotypes of offspring freq 20 HardyWeinberg principle HW equilibrium Genotype frequencies reach an equilibrium set by the allele frequencies after ONE generation of random mating Dp2 H2pq orH22p139p 2 Rq2 orR 1p Recall same equation from algebra X2 2xy y Allele frequencies 21 Results from class experiment initial frequencies AA Aa aa 70 0 30 A70 a30 22 Typical result after 1 generation AA Aa aa 50 41 8 quotBeaniesquot Random Mating Generation 2 0396 A71 a29 gt 05 U 5 3 04 539 2 03 0 E 3 02 C w 5 01 0 Typica result after 4 generations AA Aa aa A70 a30 49 42 9 Stable values HardyWeinberg equilibrium If we assume HW equilibrium we can use the relationship to estimate allele frequencies in cases of complete dominance frequency of a Jfrequency of aa genotype q xF Why is this assumption necessary 24 allele with chi Lactase persistence adult ability to drink milk is inherited as a dominant trait adults who are heterozygous L and homozygous L L can tolerate milk Recessive homozygous I I cannot Assume that the locus is in HW equilibrium Then frequency of I 25 i itiimmati allele witth Hist Lactase persistence adult ability to drink milk study done in Mexico City Tested 122 adults Found 94 who were nonpersistent they had the I I recessive genotype Genotype frequency 77 estimated allele frequency Remember dominant doesn t mean most common 26 Frequency of lactase persistence phenotype is very high in northern Europe generally gt 95 Why isn t the frequency 100 27 Frequency of lactase persistence is very high in northern Europe generally gt 95 Why isn t the frequency 100 Assume HW equilibrium If recessive homozygotes 04 q2 Heterozygote frequency 28 Importance of HW equilibrium No change in frequency no evolution If any conditions necessary for HW are not true then evolution does occur nonrandom mating affects genotype frequency not allele frequency 29 Only evolution by Natural Selection can produce longterm adaptations in a population Some Relative Fitness Components Surviva up to reproductive age Others recall definition of relative fitness 31 Forms of natural selection Selection Number of individuals in population Number of individuals in population Range of values for the trait at time 3 Range of values for the trait at time 1 Directional Selection a Camgemmlng a Engage Lumlng 32 H 33 Selection for or against extremes i E xi g E E o a E 35 a a 5 z z n Hangs oi wines or mngcoiai quotan al lime I E i 9 5 121 g u a g 5 D a a a g a E g i 5 E g Z 2 17 22 a V 2 5 39 a L a a s a a E E 2 z a Range or vaiues for wing calm mm 3 me a El Range or vaiues lav vmgrcalov an m lime 3 Disrupilva selection a Stabilizing Selection a Denggs Le mlng a Cengnqe Lelmmg Human birth weight US mid 1900 s What form of Weight selection is this 100 70 50 30 2O 20 AL CY 10 4L 0 fl Percent of population Atiieuow loomed J l CA N 1234567891011 p 481 Birth weight pounds eeeeeeeeeeee ng 34 Adaptation is a Result of Selection Dark rock habitat Light rock habitat Light fur Dark fur J gt h yrquot 3 i L Pket V differ nt habitat 35 l n Adaptation common errors1 Natural Selection stan s with random variation among descendants but the results of natural selection are not random 36 Adaptation common errors2 Natural selection does not act for the good of a species Individuals who produce more offspring aren t necessarily better than others in some cases natural selection can lead to extinction 37 Adaptation common errors3 The process of natural selection seems so wasteful Could organisms produce only the new genetic traits that will be successful and avoid the losses caused by random mutation NO In general there s no direct connection between the mutational processes and the phenotypes they produce 38
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