Genetics week 14 notes
Genetics week 14 notes Bios 206
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This 6 page Class Notes was uploaded by Becca Sehnert on Friday April 22, 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 19 views. For similar materials see Genetics in Biological Sciences at University of Nebraska Lincoln.
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Date Created: 04/22/16
Week 14 MONDAY Chapter 23 –Quantitative genetics and multifactorial traits Quantitative inheritance • Continuous variation –not all phenotypes fall into distinct categories • A scale of colors. Continuum • Polygenic –phenotype depends on input of many genes • Environment can effect phenotype • Not all polygenetic traits show continuous variation o Type II diabetes o There’s a threshold zone, but you either go up or down from there Multi-gene hypothesis • Additive alleles –contribute to phenotype • Nonadditive alleles –don’t contribute to phenotype • More additive alleles, the more pink it will be ABCD are additive alleles abcd are non-attitive Which genotype will have largest body? a. AABBccdd b. aabbCCDD c. AaBbCcDd d. AaBBCcdd e. AABbccDD • As number of genes increases, the number of phenotypic categories increases o Hard to tell difference when theres a lot o Ends up with continuous variation • 1/4 =ratio of F2 intividuals expressing either of the extreme phenotype Normal distribution • Height! Mean –average of set of measurements Variance –average squared distance of all measurements from the mean As measurements get further from mean variance increases Standard error of mean –sampling may not give you true mean of population. Measure of accuracy of sample mean Standard Deviation –square root of variance (gives you original units) Covariance –how much of variance of 2 diff traits is shared Correlation coefficient (r) –covariance divided by product of standard deviations of 2 traits Positive r = Inc. one trait correlated with increase in other Negative r = opp directions, increase 1 trait correlated with decrease in other Tallest koopa? a. Green koopa b. Red koopa Body size and running speed are negatively correlated. Which is fastest? a. 5kg b. 4kg c. 3kg d. 2kg e. 1kg Heritability • How much phenotypic variation is genetic? (within a particular enviro) • Phenotypic variance made up of genotypic variance, environmental variance, and GxE interaction variance o Heritability allows us to separate these variances o Vp = Vg + Ve + Vgxe o Phenotype depends on where they are o If lines don’t cross, no interaction • Broad-Sense heritability o H = Vg/Vp o Meas of contribution of genotypic variance to toal phenotypic variance o Includes additive, dominance, epistatic, maternal, and paternal effects o H = 1, all genetic o H = 0, all variation due to environment Genotype mostly due to environment alone (in P1) Mean height Variance Short P1 40.4 3.1 Tall P1 93.7 3.9 F1 63.9 4.7 F2 68.7 47.7 P1 F1 (3.1 + 3.9) 3.5 2 F2 Vp = 47.7 Compare variance o f parent with F1 Ve = 4.1 47.7 - 4.1 = 43.6 43.6 / 47.7 = 0.914 WEDNESDAY Narrow sense heritability • Additive variance –additive genes, genotypic variance due to additive alleles • Dominance variance –deviation from additive when heterozygous is not an intermediate, if hetero phenol is not intermediate of 2 homo —measures that deviation • Interactive variance –deviation from additive components when 2+ loci behave epistatically (often excluded), if additive components • M is mean of original population • M1 is mean of selected sub population • M2 is mean of progeny • V GV +VA+V D I • h = VA V P 2 VA • h = VE+V +A D Only look at additive variance and useful for breeders Artificial selection • Narrow Sense M2−M R h = h = M1−M OR S • • M is mean of original population • M1 is mean of selected sub population • M2 is mean of progeny • If you know what the heritability is, you can determine future generations’ increase Human Twin studies • M2 is mean of progeny • Monozygotic twins = genotypically identical o Phenotypic differences is equal to environmental variance because Vg is 0 • Dizygotic twins = • Concordance –both twins either express or do not express trait • Discordant –one twin expresses trait and other doesn’t • Concordance value is given as a percentage • Differences in concordance of MZ and DZ can give insight to genetic variance of trait o If 99 for MZ and 92 for DZ, difference is important Which is weakest genetic component? a. Hair color b. Club foot c. Measles d. Eye color e. Diabetes Look at both and if close to same for both, low genetic component. High concordance but caused by virus. Twins prolly catch virus together • Limitations o MZ might not be completely identical § Copy number variation § Epigenetic modification QTL • Region of chromosome that contributes to trait (can be mapped) • QTL mapping populations o Highly divergent lines mated to each other and F 2 examined o Lots of recombination in F2 o Can see what part of chrom is contributing to a trait • Statistical analysis can determine regions associated with phenotype of interest • After important QTLs determined, can use information for genetic engineering o Tomatoes o Instead of inserting genes, you can just selectively breed for certain traits FRIDAY CHAPTER 25 Population –group of individuals with common set of genes that lives in same geographic area and actively or potentially interbreeds Gene pool –all alleles present in population Most populations are highly heterozygous After many generations, what do you expect the frequency of dominant phenotype of a population to be? a. 0 b. ½ c. ¾ d. 1 e. You can’t tell We know how alleles behave in crosses, but doesn’t tell about population as a whole Early critics of Mendel (1901 -1908) –if Mendel correct, ¾ populations show dominant phenotype à not true! Cat survey • Looking at same population and different ratios in different traits Hardy-Wienberg • Independtly showed invalid chriticism of Mendel • Idea that ¾ will have dom allele • Allele frequency –freq of allele, not gene/genotype/phenotype (How many A in population total) Incomplete dominance Piebald SS 18 36% 0 132/402=.33 Ss 96 96 96 ss 87 0 174 270/402=.67 201 132 270 • • 3 assumptions o No mutation o No migration § Into or out of population o No selection § Force that directly changes allele frequencies by differential survival § o Large population § “Infinite population” –so allele frequencies wont fluctuate wildly just by chance § No bottlenecks § 100s-1000s are usually okay § Size of population, not of sample § o Random mating § With respect to alleles • Mutations low • • Allele frequency will not change • Phenotypic frequencies o AA=p 2 o Aa=2pq o Aa=q 2 .49+.42+.09=1 Sperm fr(A)=.7 fr(a)=.3 Eggs fr(A)=.7 fr(AA)=.7x.7=.49 fr(Aa)=.3x.7=.21 fr(a)=.3 fr(Aa)=.3x.7=.21 fr(aa)=.3x.3=.09 • Expected phenotypes: SS=p^2=.108 Chi sq x^2=1.376 ss=2pq=.441 df =1 Only 2 can actually vary ss=q^2=.451 P=.24 Accept HW .=1 IF not in HWE • One or more assumptions not true • Not a high mutation rate • CHECK ALL! Calculate allele freq, p Genotype Number p q AA 810 810*2 0 Aa 180 180 180 aa 10 0 10*2 1000 1800 200 /2000
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