Study Guide Exam 2
Study Guide Exam 2 BIOL 337
Popular in Evolution
Popular in Biology
This 7 page Study Guide was uploaded by Carolina Arreola on Saturday April 11, 2015. The Study Guide belongs to BIOL 337 at San Francisco State University taught by Routman in Spring2015. Since its upload, it has received 332 views. For similar materials see Evolution in Biology at San Francisco State University.
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Date Created: 04/11/15
Evolution BIO 337 Exam 2 Study Guide The number of babies that a zygote produces on average The ability of a an individual to go through the life cycle and produce babies The ability of a zygote to make it to adulthood If there are differences in probability among individuals to survive to adulthood we have the potential for The next part of the life cycle is the ability to become part of a mating pair If there are differences among individuals that affect their ability to become mating pairs this is caed Fecundity number of babies produced differences among individuals of their ability of how Zygote Viability Selection Adults Sexual Selection Mating Pairs Fecundity Selection Zygotes 39 Average the fitnesses of the individuals that have that genotype 39 Symbol for genotype fitness it Waa 39 Subcategories for Genotype Fitness Absolute Fitness and Relative Fitness The actual number of babies produced The absolute fitness of these genotype fitnesses that are standardized by being divided by 1 of those fitnesses I AA Aa aa Absolute Fitness 10 100 100 Relative Fitness 101001 1001001 1001001 9 Basically you take the absolute fitness given and divide it by the highest absolute tness 39 In order to make them frequencies we need to divide these numbers by the total number The total number is just the sum of the 3 genotype numbers W EwBB wBle wbb ltlt This is NOT right DO NOT DO THIS I Average Excess for Fitness of the B allele A sub B Ab pwBBW qwBbW Ab pwBBW qwBbW gt Average Fitness deviation of all the individuals who have the B allele 39 p proportion of B genes found in BB homozygotes 39 wBBW Difference in fitness between BB and the whole population 39 g proportion of B genes found in Bb heterozygotes 39 wBbW Difference in fitness between Bb and the whole population Gene flow spreads alleles around and selection just increases the frequency of the dominant allele Suppose there are 2 different populations one population favoring Cap A39s and the other population favoring little a39s This is called local adaptation adapting to your local environment Selection trying to increase the frequency of a particular allele and gene flow decreasing it It39s harder to adapt to your local situation of gene flow is occurring and migrants are constantly adding a different allele In the less polluted areas less industrial areas the white moths are more prevalent and vice versa with the dark moths Bison Beulariamoths have a higher gene flow because they fly around a lot more The ability to adapt to local places is inhibited by gene flow a How phenotypes with the environment to determine an individual39s fitness Genetic architecture refers to the genetic quotmake upquot of the phenotype such as the number of loci and the number of alleles per locus How many genes are affected How do these alleles interact with one another to form a particular phenotype this is called gene action Additive Gene Action A situation in which the effect of an allele is independent of it39s genetic context genetic context just means the other alleles that are there When this is the case you can predict the phenotype by adding up the different alleles very predictable AA Aa aa ex I 07 04 9 If the heterozygote is half way we know it is additive gene action A 05 a 02 Heterozygote is equal to 050207 NonAdditive Gene ActionThe effect of an allele DEPENDS on it39s genetic context Dominance Refers to non additive gene action within the same locus Epistasis sub category of non additive gene action The fetal hemoglobin is turned on in the fetus and then gets shut off at birth A mutation in the fetal hemoglobin locus gets continually expressed in the adult creating an adaptation to malaria 3 The factors that determine how gametes come together to form zygotes Many factors affect this such as Population Size N Mating system will determine if two Cap A39s will get together moreless frequently Geographic structure of populations 4 It39s the history of the population that has set up the current conditions traits or phenotypes that are affected by multiple loci andor the environment The field that studies complex traits is called quotQuantitative Genetics 39 We study complex traits by studying the frequency of those traits in the population we will study traits that have a continuous distribution 39 When one extreme of a phenotype is higher in fitness than the rest of the phenotypes The variance of the parent generation will be greater or equal to the offspring generation Mp Mean of parental generation 2 Mean of Offspring Mo When the mean phenotype has the highest fitness Individuals who have a phenotype that is higher or lower than the mean have lower fitness When individuals with the mean trait value have lower fitness Not very common 9 Truncation directional Selection A type of selection that divides the population into breeders and non breeders based on their phenotype If you are below the threshold you are non breeder and have a fitness of zero If you are at or above threshold you have a high fitness An example of truncation selection is all plantanimal breeding So when farmers say a pig must have a certain amount of fat in order to be sent to the slaughter house these pigs would be below threshold and be non breedersthe pigs that have little fat and are skinny are atabove threshold and will keep breeding SMsMp 9 Selection differential is equal to mean of PARENTS mean of parental generation This is the difference between the average phenotype in comparison to the rest of the population THIS DESCRIBES HOW STRONG THE SELECTION IS ON THE PARTICULAR TRAIT mean of actual breeding individuals PARENTS MQ mean of the parental GENERATION So if everyone in the population is breeding then MsMp In order to get a response to selection the trait MUST be heritable R MoMp 9 Response to selection is equal to mean of offspring mean of parental generation how much the whole population has changed from one generation to the next RS hquot2 9 Response to selection is equal to heritability times selection differential aka Breeder39s Selection hA2 The average Phenotypic similarity between parents and offspring in a population h squared is not quotheritability squaredquot its just the symbol for heritability Heritability is probably one of the most difficult things to understand in biology Rws 39 Whether a trait is environmental or genetic is dependent on what the determinant is of that trait not whether genes or the environment play a role at all I Phenylalanine gt Tyrosine enzyme phenylalanine hydroxylase If you are homozygous for this allele you have Phenylketonuria This is a genetic disease I Lgulonolactone gt Ascorbate lenzyme Gulonolactone Oxidase If you are homozygous for this allele you have Scurvy This is an environmental disease Phenotypic Variance V9 The variance among individuals in phenotype Genetic Variance V93 The variance among individuals in phenotype caused by different genotypes Environmental Variance Ve The variance among individuals in phenotype caused by different environments Let39s talk about whats happening when VpVe so where Vg Zero Here heritability will be zero hA2O When VpVg then Ve Zero heritability will be somewhere between zero and one but we don39t know where Just because a trait is genetic does NOT mean it will be heritable Additive Gene Effects The slides he talked about are on iLearn The regression line of the points plotted for p bar versus obar you should get a straight line increasing from left to right Heritability is equal to one When additive gene action is all that is occurring heritability ONE NonAdditive Gene Action Vp is still equal to Vg and Ve is equal to zero If you know the genotype you know the phenotypebut this is not related to heritability In this case the regression line is a straight line across on a not so linear graph it39s more scattered Heritability is very sensitive to allele frequencies during non additive gene action Va Additive Genetic Variance among individuals in phenotype caused by differences in genes with additive effects THE ONLY PART THE CONTRIBUTES TO HERITABILITY Vi NonAdditive genetic variance among individuals in phenotype caused by differences in genes with non additive effects VaVp Heritability h 2 Vp Va Vi Ve Va is the only factor that contributes to heritability To measure heritability you do regressions If you don39t have data from parents how do you compare parent to offspring You can look at any set of relatives and predict what heritability would be This is because when you look at relatives you assume ALL SIMILARITY IS CAUSED BY SHARED GENES not by shared environment 9 Logistical Complexities Sample size must be large in order to get an accurate number for heritability Adjustments and assumptions must be made for shared envrionments Maternal Effects When offspring shares environment with parent 9 Conceptual Complexities Heritability hA2 refers to phenotypic similarity between parents and offspring on average in a population hA2 doesn39t predict individual phenotype hA2 doesn39t predict family phenotypes is Ve gt Zero OR if Vi gt Zero hA2 can change in different populations even if they are in the same environments hA2 can change for the same population in a different environments Heritability tells you NOTHING about the causes of differences among population 9 An example of this is the Race lQ controversy Although the IQ trait is heritable it is HIGHLY affected by environment Vp Va Vi Ve VaVp h 2 Artificial Selection Selection that occurs when human beings determine the fitness of individuals based on their phenotypes Most commonly found in plantanimal breeding Natural Selection When the environment determines the fitness of individuals even when human beings determine the environment Showed us a slide on iLearn called quotLong term selection on oil content in maize quot This experiment was done over 80 generations 80 years There are 2 different selections one for higher oil content and one for lower oil content Environmental differences keep you from getting the results you would predict to get according to the R equation we talked about last time If selection is always occurring then genetic drift is also always occurring There is an asymmetry between the directional selection upwards vs downwards Why didn39t the line going down not go as far as the line going up Because there is a minimum amount of oil needed to grow corn thats why the line with the low oil content has a shorter line than the upward selection Cliff Swallows Birds The longwinged birds were getting hit more often than the birds with the shorter wings As a whole population the wing length has then decreased Disruptive Selection Example When the mean phenotype is not favoredTom Smith studied African black bellied seed cracker birds and green bulbuls He found that in the forest birds have short round beaks and in the ecotone the birds have long sharper beaks there wasn39t really any birds that have medium sized beaksDrosophila species were measured for the length of the vein under their 4th wing The researcher collected this data for several of these drosophila and did selection Sexual Selection difference in an individual39s ability to obtain mates Sexual Dimorphism When male and females have different external morphologies
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