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Evolutionary Bio Test 2 Week 4

by: Adam Rodenberg

Evolutionary Bio Test 2 Week 4 12050 - BIOL 3350 - 001

Adam Rodenberg

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About this Document

This set of notes includes everything Dr. Sears covered in class plus all of the vocabulary and major notes from the textbook from this week.
Evolutionary Biology
Dr. Michael Sears
Class Notes
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This 4 page Class Notes was uploaded by Adam Rodenberg on Friday February 26, 2016. The Class Notes belongs to 12050 - BIOL 3350 - 001 at Clemson University taught by Dr. Michael Sears in Spring 2016. Since its upload, it has received 25 views. For similar materials see Evolutionary Biology in Biological Sciences at Clemson University.


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Date Created: 02/26/16
Evolutionary Bio Test 2 Week 4 This set of notes includes everything Dr. Sears covered in class plus all of the vocabulary and major notes from the textbook from this week. 2/23/16 Not planning on having equations provided on the exam Know hardy Weinberg like the back of your hand Linkage disequilibrium­ Evolution at 2 loci­ 2 physically linked loci (next to each other on the same chromosome) Populations can have identical allele frequencies but different chromosome frequencies ( one in  HWE but the other might not) In order to calculate if this pop is in eq. we calculate the freq. on chromosomes carrying a and A  allele. If in equilibrium the frequencies should be equal.  The coefficient of linkage disequilibrium, symbolized by D, is defined as gABgab−gAbgaB  <typo in book gAB = ps, gAb = pt, gaB = qs, and gab = qt  D =psqt−ptqs = 0 D ranges between ­0.25 and 0.25 ^genotype frequencies of the gametes Two loci in a population are in linkage equilibrium when the genotype of a chromosome at one  locus is independent of its genotype at the other locus. Two loci are in linkage disequilibrium when there is anonrandom association between a  chromosome's genotype at one locus and its genotype at the other locus. Freq of A 8 freq of B should give you the genotype freq of AB r = recombination rate d = disequilibrium while in diseuilibrium, chromosome frequwncies move closer to equilibrium with each  generation Linkage equilibrium criterion 1. The frequency of B on chromosomes carrying allele A is equal to the frequency of B on  chromosomes carrying allele a.  2. The frequency of any chromosome haplotype can be calculated by multiplying the frequencies of the constituent alleles. For example, the frequency of AB chromosomes can be calculated by  multiplying the frequency of allele A and the frequency of allele B. 3. The quantity D, known as the coefficient of linkage disequilibrium, is equal to zero 3 things can cause linkage disequilibrium­ selection, genetic drift (only in a finite population)  and admixture ( Experiment with flies­  2 populations in linkage disequilibrium on different ends of spectrum  both returned to close to equilibrium after several generations If locus A and locus B are in linkage equilibrium—then selection on locus A has no effect  whatsoever on allele frequencies at locus B. On human chromosome 22, most pairs of loci are in linkage equilibrium situated near enough to  each other on the same chromosome that crossing over between them is rare. If a gene is young, it is likely to have a high disequilibrium value  If a young gene is common, selection probably acted on it.  Parthenogenesis­ offspring develop from unfertilized eggs – making an exact copy of the mother Null model to test how quickly one sexual strategy would outcompete the other­  1. A female's reproductive mode does not affect how many offspring she makes. 2. A female's reproductive mode does not affect the probability that her offspring will survive. Asexuals reproduced much faster than the sexuals, but asexual takeovers rarely happen­ has to be some selective advantage for male­produced offspring Sex­ allelic segregation and genetic recombination – restores HWE and linkage equilibrium Outcrossing­ an adaptation for maintaining fitness in the face of deleterious mutations C. elegans example­ asexual individuals grow unfit over time­ higher mutation rate selected for  more frequent outcrossing, and more males Muller’s ratchet­ asexual populations accumulate deleterious mutations through time Sexual selection through crossing over can reduce the deleterious mutations and result in  recombination of beneficial alleles, which leads to more genetic diversity for selection to act on  (good) 2/25/16 Don’t need to read chapter 9, too much info on the test, going over it today anyway? Disequilibrium vs HWE Linkage disequilibrium – broken by  Look at example in book about Crohn’s disease 3 things that push a population into linkage disequilibrium­   genetic drift, ____, _____ Know how to calculate the b statistic Closer to 0, the less disequilibrium Know how to calculate d, allele frequencies, ____,  Math problems will be posted on mindmeister Know all of the equations­some might be on the test, be prepared for none, won’t be labeled,  might need to be rearranged  Calculate fitness, avg fitness, chi square, interpret them,  Know everything on the review link under week 6  Go through case studies in the textbook and the ___­ look at their concepts  Sex can save you from mullers ratchet­ says that the deleterious mutations that accumulate from  asexual reproduction are likely to be at least balanced out in the population  When would it be advantageous to have more alleles in a population?­ more stressful  environment 2/26/16 Ch. 9 Quantitative genetics­ branch of evolutionary biology that provides tools for analyzing the  evolution of multilocus traits Qualitative traits­ traits that allows characters to be qualified by looking at them Quantitative traits­ characters with continuously distributed phenotypes Quantitative trait loci (QTLs)­ portions of the genome that influence quantitative traits QTL mapping­ the collective name for a suite of related techniques that employ marker loci to  scan chromosomes and identify regions containing genes that contribute to a contribute to a  quantitative trait Heritability­ the fraction of the total variation in a trait that is due to variation in genes Phenotype variation (V )­Ptotal variation in a trait Genetic variation (V )­ variation among individuals due to variation in their genes G Environmental variation (V )­Eariation among individuals due to variation in their environments Heritability equation (Broad­Sense heritability)­   V /V =(V /V +V ) G P G G E Midparent value­ the average of the parents Midoffspring­ average of the offspring (if more than 1) Narrow­sense heritability­ the ratio of additive genetic variance to the total phenotypic variance Directional selection­ when fitness consistently increases(or decreases) with the value of a trait Stabilizing selection­ when individuals with intermediate values of a trait have highest fitness Disruptive selection­ when individuals with extreme values of a trait have the highest fitness


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