Evolution Notes: Week Four
Evolution Notes: Week Four BIO318
Virginia Commonwealth University
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This 4 page Class Notes was uploaded by Jayda Abrams on Sunday September 25, 2016. The Class Notes belongs to BIO318 at Virginia Commonwealth University taught by Dr. Turbeville in Fall 2016. Since its upload, it has received 17 views. For similar materials see Biology: Evolution and Biodiversity in Biology at Virginia Commonwealth University.
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Date Created: 09/25/16
Week Four Tuesday 9/20/16 and Thursday 9/22/16 Review: Selfing is nonrandom mating. F= division of the gamete pool into two types. F= Self and 1-F= Outbred Wright F Statistic / F Statistic Inbreeding can be bad for a population because it exposes recessive mutations at a higher rate! Natural Selection Round 2 Selection Coefficient- The measure of strength for natural selection, for or against a specific phenotype or genotype. For this class: Lower S = measure of strength of natural selection against a specific genotype. Fitness of a genotype is given by subtracting S from it. Most fit = 1 Less fit= 1-S Fitness AA Aa aa 1 1 1-S Works like dominant and recessive. In this example the dominant allele is the most fit but this is not always the case. For incomplete dominance Codominance- A phenotype is half way between 2 dominant traits. Example: Red and White flowers make pink. Fitness AA Aa aa 1 1-hs 1-S H quantifies how incompletely dominant the relationship is. Example: If H = .5 that tells you it is half way between 1 and 1-S. What if H is equal to 1? This creates the equation 1-S and H 0-1. Fixation- When an allele goes to a frequency of one this process is called fixation. Many different environmental forces result from fixation. Example: Selection Loss- Opposite of fixation. Allele frequencies decrease to zero. Population genetics is a huge part of biology and uses math and graphs. What is frequency independent selection? Fitness does not matter to its frequency in the population. PopG Graphs Selection is better in incomplete dominance. Random Chance genetic drift- Random change Black ridged lines on graph= Genetic Drift Smaller population sites are more likely to deviate from random chance/ genetic drift Genetic Drift can cause fixation and loss of alleles over time Larger population take longer for alleles to be lost or fixed Small populations genetic drift is more important in big populations genetic drift is less important Always assume genetic drift because there is no pattern. The changes are subtle and the population size can never be infinite. Genetic drift causes differences in all populations Migration makes populations stick together and the set of populations act as one big population Genetic drift is the stronger of the two evolutionary forces- Two evolutionary forces are migration and genetic drift. When multiple evolutionary forces occur pick the strongest one and keep track of the relative strength. Identity by Descent (IBD)- Occurs without inbreeding. Identity = same allele By descent = Descent on pedigree from one allele in the past Effective population size (N ) e E Stands for Effective Wright Fisher Model (WFM)- HWE without an infinitely large population. WRF= HWE with genetic drift Example: There are 7 billion humans on this planet, however the WFM is equal to 10,000. F Stat Heterozygosity decreases and will go to zero eventually depending on if inbreeding is on purpose or on accident. Population Structure: How allele frequencies vary across more than one population. FST – modification Concept that measures the different allele frequencies Frequency is > 1 because individuals are in different finite size populations Wahlund Effect
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