Bio1B Evolution 3 Last lecture Natural selection principles lines of evidence in the Origin Descent with modification Estimation interpretation of phylogeny Some major insights about the Tree of Life 3 kingdoms Archaea Bacteria Eukarya Metazoan origins relationships not covered Today More history Darwin Mendel the Neodarwinian synthesis Mechanisms of evolution Evolution in populations population genetics Allele genotype and phenotype frequencies Predicting genotype freq s Hardy Castle Weinberg Equilibrium Application Null model for evolution Application Predicting heterozygote frequencies for recessive traits 1 Mendel s principles of inheritance 1865 see Ch 14 Alternative versions of genes alleles account for variation in inherited characters For each character an organism inherits 2 alleles one from each parent If the 2 alleles at a locus differ then the dominant allele determines phenotype The 2 alleles for a heritable character segregate during gamete formation Law of Segregation Each pair of alleles segregates independently of others during gamete formation for unlinked genes Mendel s garden Brno 2 Dominance of purple P over white p flower color Fig 14 5 P Generation Co dominance heterozygote is intermediate pink in snapdragons Fig 14 10 P Generation Purple flowers PP P Appearance Genetic makeup Gametes White flowers pp p Red CRCR White CWCW Gametes CR CW F1 Generation Pink CRCW F1 Generation Appearance Genetic makeup Purple flowers Pp 1 Gametes 2 1 P 2 p Gametes1 2 CR 1 2 CW F1 sperm P p F2 Generation 1 P PP F1 eggs p Pp Pp 3 pp 1 F2 Generation Eggs 1 R 2C 1 2 CW 2C R 1 2C W CRCR CRCW CRCW CWCW Sperm Genotype and allele frequencies for a locus with two alleles 4 Futuyma 2nd Ed Hardy Weinberg Equilibrium Gametes for each generation are drawn at random from the gene pool of the previous generation general case male gametes 80 CR p 0 8 q2 A2A2 Sperm CR 80 A1A1 p2 A1A2 2pq A2A2 q2 CW 20 p2 pq 64 CRCR 16 CRCW CR 80 qp A2A1 pq A1A2 CW 20 Expected genotype frequencies p2 A1A1 Fig 23 7 Eggs f A2 q f A1 p female gametes f A1 p f A2 q 20 CW q 0 2 qp 4 CWC W 16 CRCW q2 Hardy Weinberg Equilibrium Predicts genotype phenotype frequencies from allele frequencies Genotype frequencies in expected proportions in a single generation Allele genotype frequencies constant across generations inheritance alone does not cause evolution Assumptions Random mating for this gene trait No mutation selection migration Large population no drift 6 Applications of HWE A null model for evolution Deviations from expected proportions indicate something interesting but what Cystic fibrosis Mapped to chloride transport gene on chromosome 7 Common mutation F508 is recessive and at p 0 02 in caucasian population F het 2pq 0 04 carriers F hom p2 0 0004 affected Predicting frequency of heterozygotes for recessive alleles e g cystic fibrosis 7 Hardy Weinberg genotype frequencies as a function of allele frequencies at a locus with two alleles Futuyma 2nd Ed 8
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