week 4 409
U of L
Popular in Evolutionary Biology
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This 2 page Class Notes was uploaded by Mary-elizabeth Notetaker on Friday September 16, 2016. The Class Notes belongs to Bio 409 at University of Louisville taught by Jeffery Bara in Fall 2016. Since its upload, it has received 6 views. For similar materials see Evolutionary Biology in Biology at University of Louisville.
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Date Created: 09/16/16
Week 4 Tuesday, September 13, 2016 3:52 PM Modern syntheses- resolved apparent conflict btwn mendelian genetics and mech of NS ○ Change in relative abundance of diff phenotypes over time can be linked to changes in freq(relative abundance) of genotypesthat encode(influence)them Pop genetics- evol viewed as change in allele freq across generations Hardy-weinberg principle- describes null model of evol- described allele and genotype freqs over time in pops in which no evol is happening ○ Ex) null model graph ○ Pop- group of interbreeding indivs & offspring ○ Life cycle of idealized pop ○ Relative freq- proportion of total and ranges btwn 0-1 freq of AA individuals= (#AA indivs/total# indivs) Ex) 120 AA, 40As, 40aa..frew A and a? □ # A alleles=(2x120)+40=280 □ Total allele #=2x(120+40+40)=400 □ Freq A=280/400=0.7 □ Freq a= 1-0.7=0.3 Freq of all alleles at a locus taken together=1.0 ○ HW always true: Freq(A) + freq(a)=1.0 Convention:freq A=p, freq a=q p+q=1 ○ Freq=prob of selection that allele at random from the pop ○ Heterozygosity-measure of genetic diversity Freq of hetero in pop(one locus) Proportionof org's genes that are hetero(all loci) Prob that if you pulled 2 alleles from pop at random they would not be the same(onelocus) Observed vs expected heterozygosity: □ Ho= observed heterozygosityis actual freq of heteros in pop □ He= expected freq of heteros can be calculated from allele freq if you make some assumption To know actual heterozygosityfrom allele freqs, need actual geno freq or allele freq + info that your assumptions are met ○ Null model about evol would describe what happens in pop when no evol is occurring 5 forces of evol: □ Mutation □ Migration □ Selection(diff survival/reproductivesuccess of certain alleles/gene combos) combos) □ Genetic drift(driven by chance events) □ Non random mating ○ Generate zygotes from gametes Proportionalpunnett square shows possible egg and sperm in proportion to the freq of the alleles in the pop 2 central true facts about prob: ○ Prob of 2 indep events both occurring is the product of their probs Ex) prob for pair of siblings, older will be a boy and younger girl? □ Prob of girl x prob of boy= .5 x .5=0.25 ○ Prob that one of a possible sset of mutually exclusive events will occur is the SUM of their probs Ex) prob for given birth that either boy or girl will be born? □ P child is boy + p child is girl= .5+.5=1.0 ○ …both rules used when calculate prob of heteros ○ F(Aa)=2pq only true under HW conds Transitions from zygotes to adulthood and reproductive age(under HW no changes in allele freq) HW conclusions: when assumptions hold… Allele freqs in pop will not change gen after gen Allele freq are given by p & q, then eq genotype freq qill be p^2 2pq and q^2 If Pop begins out of HWE but all assumptions are met, single gen of random mating will restore HWE eq genotype freqs ○ Alternative hypoth: if assumptions not met, 1 or more of 5 forces of evol must be in play Allele freq DO change over time Genotype freqs do not match those expected based on p & q Adding selection into HW: diff survivorship and reprod incorp's into transition from zygote to adult mathetmaticallyas prob of making it to adult stage ○ Use comparisonof allele freqs btwn gens to evolution Since allele freqs don’t stay constant over time like HW would say, some evol force must be acting ○ Use comparisonof observed vs expected heterozygosityto detect evol Predicts under selection observed genotype freqs can fail to match the expected freqs □ Genotype not expected based on allele freqs ○ Use comparisonof observed vs expected heterozygosityto detect evol Expected freq of B1B2 is 2pq if pop were in HW and there was no selection If genotype freqs don’t match expected freqs based on HW theory, someevol force like selection must be acting
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