Genetics Notes week 15
Genetics Notes week 15 Bios 206
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This 6 page Class Notes was uploaded by Becca Sehnert on Friday April 29, 2016. The Class Notes belongs to Bios 206 at University of Nebraska Lincoln taught by Dr. Christensen in Fall 2016. Since its upload, it has received 14 views. For similar materials see Genetics in Biological Sciences at University of Nebraska Lincoln.
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Date Created: 04/29/16
WEEK 15 MONDAY Allele frequencies for sex-linked traits: males have only 1 allele of each x-linked gene • Still count alleles • O is 83 • o is 208 • Total is 291 • p = 83/291=.29 • q = 208/291=.71 What are expected values, if HWE for x-linked traits? • Prob that will inherit O from mom is .29 • Prob that will inherit p or q for males, is same as p and q • Females o Freq of AA = p^2 o Freq of Aa =2pq o Freq of aa =q^2 • Expect males to be ½ of total and females to be ½ total number o Have to divide total number by 2 cuz only get half females and half males o DF = 3 o P ~0.07, fail to reject HWE What about complete dominance? IF in HWE, allele frequencies can be estimated Longhaired cats • L_ =148 • ll=61 • Total =209 • Freq of L_ = p^2 + 2pq =148/209 =.292 • Freq of ll =q^2 = 61/209 =.54 • P = 1-q =.46 • CHI SQUARED VALUE IS 0 and DF IS 0 o Circular reasoning o Statistical nonsense Estimate allele frequency, p, of non dilute allele, D Geno # D_ 220 dd 36 total 256 Q^2 =36/256 SqRt that is .375 1-.375 = .6=p Dominant allele frequency doesn’t overtake population S allele (piebald spotting) stayed same over lots of sampling Orange hasn’t increased, it bounces around Not a lot in other countries (selection? Founder effect?) Long hair is hard to score so numbers move around Dilute –went down this year, thanks Internet Dominant white is low everywhere Estimate freq of curly winged allele in flies Geno # curly 300 strait 100 total 400 a. .13 b. .5 c. .75 d. .87 e. Not enough information Straight is dominant a. .13 b. .5 c. .75 d. .87 e. Not enough information Q^2 is 300/400 and sq rt of that DON’T SUBTRACT FROM 1 If straight dom, q^2 is 3/4 Curly is dominant a. .13 b. .5 c. .75 d. .87 e. Not enough information What is p? 100/400 sq rt (10/20)=.5 What accounts for diff allele frequencies in diff, isolated populations? • Mutations –usually very rare • Migration –probably significant in cats (cant get far on their own, mile per generation) leads to FOUNDER EFFECTS • Selection –natural selection (W?) or artificial selection (Purebreds!) • Small population size –bottlenecks and drift What causes allele freq to change? At least 1 HWE assumptioin isn’t true WEDNESDAY! (Only one more day!!!! J ) Natural selection is a major force driving allele frequency change • Recessive lethal mutation, t o Huntingtons o Hetero, Tt, with 100% population o Q=.5 o Next gen is 1:2:1(die) § Now its just 1/3 TT and 2/3 Tt o New frequency q=1/3, p=2/3 o Next gen § (2/3)^2=4/9 TT § 2(1/3)(2/3)=4/9 Tt § 1/9 die o New ratio is ½ TT, ½ Tt § Q=1/4, P=3/4 o Next gen is § (3/4)^2=9/16 TT § 2(1/4)(3/4)=6/16 Tt § (1/4)^2=1/16 tt(die) o New ratio is 9/15 TT, 6/15 Tt § Q=1/5, p=4/5 o Ratio of t goes down by q^2 every generation • After 100 Generations, q=.01 (2% hetero) • To reduce to .0001 will take 1000 gen • Weaker selection changes allele frequencies at even slower rate • IF heterozygous is good, then that’s how the recessive bad persists Selection acting on quantitative traits can be directional, stabilizing, or disruptive Migration and gene flow can alter allele frequencies • Species divides to geographically separated populations, allele frequencies differ over time due to migration o Similar to founder effect except that’s in a small population Genetic drift causes random changes in allele frequency in small populations • When # reproducing individuals too small to ensure all alleles in gene pool will be passed on to next generation in existing frequencies o Drifting down a river on a log • May result in one allele disappearing, or becoming fixed • Can arise through founder effect, when population originates from small# • Similar to bottleneck –squeezed to small population then expands again Autosomal recessive disease found in 1 in million people Approx how frequent are hetero carriers (Assuming HWE) a. 1 in 500 b. 1 in 5000 c. 1 in 50,000 d. 1 in 500,000 e. Not enough information Q^2=10^(-6) q=10^(-3) 2pq=2*.999*.001 = 1/500 Nonrandom mating changes genotypic frequency but not allele frequency • Star belly sneeches o Put non-star belly people in phenotype machine o Mating systems finally coexisted • Positive assertive mating (PAM) –similar genotypes more likely to mate than dissimilar one o Obligate self-crossing –pollen shed before flowers even open • Negative assertive marriage (NAM) –dissimilar genotypes more likely to mate than similar ones o Obligate outcrossers –need other type of trees to add genotype dissimilarities. Will not self with self • Inbreeding –mating individuals are related o Increases proportion of homozygotes in population, and completely inbred population theoretically will consist only of homozygotes o Self-fertilization is form of inbreeding common in plants o Homozygotes o Extinction of population is different than extinction of an allele NIH defines rare disease as one afflicting fewer than 1 in 200,000 people. If 2pq is less than 250 if q is less than 200,000 it’s a rare disease a. Yes b. No c. Not enough information FRIDAY #10 practice –draw it out Girl 1 v-/Y st+/st+ boy X v+/v+ st-/st- GEN Gndl 2 v+/Y st+/st- boy X v+/v- st+/st- Gen 1/2 1/2 v+ v- 3/4 st+/_ 1/4st-st- 3/8. 1/8. 4/8. MIDTERM 2 #7 • 4 segregating but only 8 genotypes • DO 2 at a time, as a gross • Forget about ringo so add identical ones together • See that J and P never segregate because they are always inherited together. Can map it as such so then compare with calculations • Add back in R and see that it is always 50% so its probably unlinked o Either 50+ cM apart on same chromosome or different chrom. o Unlinked cuz cant assort into recombinants MIDTERM 2 #13 +++ 36 w++ 42 g++ 162 j++ 10 wg+ 8 wj+ 166 gj+ 40 wgj 36 g++ .+wj G IN j++ MIDDLE .+wg HOMEWORK #11 look at lecture 37 • Allele frequencies for x-linked gene • Look at males for yellow (421/(421+13)) =.97 • If yellow is dominant, its P o Q=.03 o Assume q^2 would be .0009*434 o .97^2 • If in HWE, it is consistent with yellow being recessive and not consistent with yellow being dominant
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