Chapter 23: Evolution of Populations
Chapter 23: Evolution of Populations BYS 120
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Date Created: 12/01/15
Chapter 23 Lecture Notes 0 Gene segment of DNA Alleles different gene 0 Changes in the nucleotides Locus physical location of a gene on a chromosome 0 Character hertiable freature 0 Eye color Trait variant of character 0 Blue eyes 0 For each locus nonsex linked a diploid organism inherits 2 alleles from each parent Mendel39s model of inheritance 0 Complete dominance 2 different alleles dominant allele is fully expressed while recessive one is masked o Incomplete dominance 2 different alleles are mixed together 0 2 alleles for each character segregate during gamete production meiosis Law of segregation De nitions 0 Genes are named after their mutant or rare trait 0 Dominant alleles are capitalized recessive are lower case 0 Homozygous same gene PP or pp 0 Heterozygous different gene Pp o Genotype combination of alleles o Phenotype expressed trait Polygenetic inheritance 0 Height skin or coat color 0 Continuous 0 Quantitative characters 0 Quantitative data came about through polygenetic inheritance additive effect of 2 or more genes 0 The alleles of different genes are contributing to unit of trait EX coat color in mice 0 Assume that mouse coat color is controlled by 3 genes having only 2 aees each 0 1 dominant1 more brown pigment o 1 recessive1 ess brown pigment Multifactorialcharacter o Phenotype can depend on environment as well as on genes Height weight intelligence 0 A genotype has potential range of phenotypes called a norm of reaction HardyWeinburg 0 Given allele frequency pA and qa 1pquot2 2pq qquot2 1p q o Pquot2 frequency of homozygous dominant o Qquot2 frequency of homozygous recessive o 2pq frequency of heterozygous 0 Holds true if population is in equilibrium 0 Assumptions No migrations Large effective population No mutation new alleles Random mating No natural selection 0 Deviations from HW equilibrium can be assessed using a xquot2 chi squared formula HW deviation 0 In a population the frequency ofA is 32p and a is 68q o 40 AA 0 38 Aa 52 aa o Is the population in equilibrium P32 q68 Observe Expected Expected d frequency frequency AA 40 32quot2107 113013 Aa 30 2326844 4413057 aa 52 68quot246 4613060 Sum 130 1 130 0 Use xquot2 sum of observedexpectedquot2expected to see if its in equilibrium Xquot2 4013quot213 3857quot257 5260quot260 561 64 101 o 635 o Is xquot2 is greater than 3841 it39s not in equilibrium Reject hypothesis 0 Why not in equilibrium 0 Check assumptions PA8 o 18q o 2qaa o Qa04 Genetic variation 0 Individuals can also vary across populations of same species geographical variation 0 Variation across geographic range of a species could either be due to adaptation natural selection or by chance random genetic drift Mutations are the ultimate source of genetic variation 0 Always occurring 0 Can be deleterious neutral and advantageous o Condons pair of 3 nucleotides 0 64 gt 3 are stop codons 0 Neutral silent or synonymous No protein change 0 Deleterious replacement nonneutral and nonsynonymous Protein change True or false individuals evolve not populations 0 False The majority of mutations observed are 0 Neutral 0 Other types of mutations o Insertions and deletions indels Sequence is deleted or new DNA is inserted Transportable elements sel sh DNA ALV element in humans less than 1 million times about 10 of genome 0 Chromosomal Inversion Breaks and inverts over ips gene order 0 Can cut genes in half Translocations Switching pieces with another chromosome Duplicating and deletions More duplicateddeleted more affected Nondisjunction Other sources or variation 0 Migration 0 Individuals moving to and from a population 0 Sexual reproduction Creation of new allele combinations due to recombination and assortment Change in the level of variation 0 In addition to new mutations a population39s gene pool will also change dueto Migration gene ow 0 Random genetic drift Natural selection Nonrandom mating Gene ow 0 Via migration can introduce new variations to population Insecticide DDT resistance in mosquitos culex pipien o Across individuals from different populations continuously mixes gene pool Homogenizes the variation across populations Prevents genetic divergence EX D Melanogaster o 2 main alleles of alcohol dehydragenase gene fast and slow 0 An incline in alleles frequency relative to latitude Random genetic drift Q Is a quarter a fair coin Flip 4 times 3 heads 1 tails Flip 1000 times 750 heads 250 tails 0 Because sampling process is larger uctuations in results with smaller number of ips Rando genetic drift has the greatest effect on what population size 0 Small CquotRred O CquotWwhite 0 Generation 1 pfrequency of CquotR7 qfrequency of CquotW 3 0 Generation 2 5 plants have offspring P5 q5 0 Generation 3 2 plants have offspring P10 q0 O Dramatic change in allele frequency just by chance Genetic drift 0 When species move to new areas only a few individuals actually colonize little variation Founder effect I Islands tend to be colonized by few individuals Can occur when population size is drastically reduced Bottleneck effect Case study Greater Prairie chicken 0 Tympanuchus cupido 0 Population decreased due to habitat loss in IL 0 Signi cant loss of variation occurred due to bottleneck effect Genetic drift key points 0 More signi cant in smaller populations 0 Responsible for uctuations of allele frequency 0 Eventually leads to loss of variation 0 Can cause deleterious alleles to become xed Could effect of genetic drift ever be strong than natural selection 0 Yes if population size is small Natural selection and evolution 0 The process which certain alleles are favored selected because they perform better higher tness than other alleles in the population 0 Natural selection occurs in the phenotype not genotype Fitness 0 An individual ls relative to that of other individuals of the same species in the same environment relative tness 0 Relative tness is dependent on natural selection Many forces affect evolution 0 Natural selection could sometimes be very strong Lethal disorders 0 Other forces like genetic drift can drastically alter effects of natural selection Models of selection 0 Directional selection for one extreme phenotype O Disruptive selection middle is lower mean Favors two extremes O Stabilizing selection against the extremes Directional selection case study 0 Medium ground nch Geospize fortis O In Galapagos islands they feed on seeds of Spurge small seeds Caltrop hard and large seeds 0 Peter and Rosemary Grant observed nch populations for many years 0 Beak depth was hertiable Offspring looked like parents Variation performance 0 Beak depth Time to crack big seeds 11 mm 10 seconds 105 mm 15 seconds 8mm Never gives up 0 1977 the island got hit by a severe drought 0 Most small seeds died 0 When the nch population recovered their beaks were 4 deeper Sexual selection 0 Selection of character associated with higher access to males 0 lntrasexual 2 males ghting more mating rights 0 Intersexual Males impressing females 0 Both support extreme phenotypes Intersexual selection 0 How did female preference of these structures evolve Good genes hypothesis D If males have enough energy to spend to support these traits it likely means he39s genetically healthy 0 What is preventing males to get bigger and more extreme traits Directional selection 0 Trade offs Easy picking for predators Metabolism Negative affects of extremes 0 End up with multiple forces of pushing and shaping distribution Balancing selection 0 Maintenance of genetic variation via natural selection 0 Heterozygote advantage Heterozygote has higher tness Sicklecell amenia is a recessive disorder that transforms red blood cells into a quotsicklequot Stuck in capillaries and causes in ammation in joints especially Sickle cell amenia O Heterozygote are protected against some malaria symptoms 0 No malaria Malaria SS Normal Symptoms 55 Normal Reduced symptoms 55 Sicklecell Sicklecell EX environment chooses which allele is advantageous or deleterious O Frequencydependent selection Fitness of a genotype is dependent on its frequency in population Relative tness is higher at lower frequency 0 Bumble bees and elder ower orchids Elder ower orchids trick bees by attracting them but offers no award Bees visit 1 color then another color Within a path of the less common color gets more visits pollination