2 Variation with my notes .pdf

2 Variation 23 Friday, 6 October 2023 2 Varia'on 23 13:59 Heterosis refers to the phenomenon that proge or crosses between species exhibit greater and fertility than both parents. (maintains vari Heritability is a measure of how differences in their traits. 80% of the reason you are the heigh...

2 Variation 23 Friday, 6 October 2023 2 Varia'on 23 13:59 Heterosis refers to the phenomenon that proge or crosses between species exhibit greater and fertility than both parents. (maintains vari Heritability is a measure of how differences in their traits. 80% of the reason you are the height eny of diverse varieties of a species r biomass, speed of development, ation ) w well differences in people's genes account for you are is due to genes The selection differential S = (trait mean after selection) - (trai negative value if smaller individuals have higher survival. R = h2 S. R is the response to selection, S is the selection differen heritability. This is the workhorse equation for quantitative genetic The complicated process by which selection causes genetic cha into two components, phenotypic selection (S) and response to the relationship between phenotype (trait values) and fitness (s latter is determined by the mapping from genotype to phenotyp it mean before selection) which gives a ntial, and h2 is the narrow-sense cs. ange within a population is decomposed selection (h2). The former determines survival and reproductive success). The pe. the relationship between phenotype (trait values) and fitness (s latter is determined by the mapping from genotype to phenotyp The selection differential (S) is the difference betwee group and the mean of the population. multiply the heriability by the selection differ The mean in the next generation is the mean in the previous ge response to selection. survival and reproductive success). The pe. en the mean of the selected rntial. ( not by heritbabilty squared ) eneration (BEFORE selection) plus R, the Same figure as last lecture, there is tree cutting and only oran trees and live. Transmitted to next generation, multiply s by h squared, givin next generation If both of these cases there is a reduction of variation Selection reduces variation If continued, you would expect genetic variation is used up ngutans with ling arms stay and ng predicted mean of adults in p. If both of these cases there is a reduction of variation Selection reduces variation If continued, you would expect genetic variation is used up The stronger the selection, the more rapid the reduction And hence the traits that are closely related/associated to variability Bloke trying to assay genetic variation - gel electrophoresis Did so on allozymes p. of variation occurs o fitness should have less Simplest of variation - polymorphisms In biology, polymorphism is the occurrence of tw or forms, also referred to as alternative species wo or more clearly different morphs phenotypes, in the population of a Barnacles - read over this just wasn't listening Barnacles - read over this just wasn't listening Not always simple polymorphisms - can have continuous variati understand Thousands of genes affect human height - hard to understan ion, which is harder to nd quantitative genetics - to understand continuous variation Fisher developed partition of variance Vp is sum of va vg ve Vp is total phenotypic variation ( e.g. if we all measu height and variance of it using equation ) Va - genetic variation due to genetic effects Vg - non genetic variation, epistatic etc Ve - environmental affects, called error term but isn ured ourselves and found our n't about error Ve - environmental affects, called error term but isn The heritability is the additive genetic varianc + year + brood + residual. Va/ Vp This experiment took chicks of one nest and swapped with origin environment components from genetic component No relationship of bill depths of chicks and foster parents, but is and true parents Means strong genetic component compared to environment Coefficent of variation of a traint Relationship between mean and variability n't about error ce / total variance. In this example total variance = additive nal parents, to separate s a relationship of beaks of chicks Coefficent of variation of a traint Relationship between mean and variability Can compare variability of traits by dividing standard de variation. Larger things normally have bigger variation The coefficient of variation (CV) is the ratio of the stand The higher the coefficient of variation, the greater the level of ev by mean to give coefficient of dard deviation to the mean. f dispersion around the mean. Life history trait = closely correlated to fitness and strong s Life history traits go up more quickly - means on average life h heritable than morphology traits. Agrees with statement that traits most closely related to fitnes Life history traits are less variable and hence less heritable a But heritabiity isnt good factor for varaition selection history traits are less variable and ss ( life history ) has less variation as heritbablity fomrula is built from variance But heritabiity isnt good factor for varaition This lad houle used In this case there's more variation in life history trait closely related to fitness Doesn’t show it in last diagram because heritability was Fitness/selection does not use up variation ts ?? More variation in traits s given as ratio How can we explain variation then? Is it not reliant on different contexts? Proposals 1. Variation is selectively neutral 2. Mutation-selection balance - has to be true, becau mutation 3. Balanciing selective forces Mutation selection balance - there's a balance between the two Mutation is ultimate source of variation use source of variation is Maintaining variation Kuru In new guinea there was a neurological disease, result of pr Prion is protein which has different formations and wrong f disease. Because the women ate dead brains of ancestors causing tr Carrying heterozygote for the PRNP129 gene confers res Sickel cell anemia, Heterozygote - RBC deformed but not loads and confers resistance to malaria Homozygote for either allele Evolution in short term progresses from standing variation - look up rion disease formation cause plaque in brain causing ransmission of prion disease sistance to prion disease Carrying heterozygote for the PRNP129 gene confers res Favours maintenance of both alleles in population ( same as sickle cell anaemia ) Mechanism that’s common to maintain variaiton Frequency dependency selection Looking at reproductive success of plants due to frequency o Declining reproductive success with increasing frequency of morph ) Line going horizonal means equal success of yellow and pur successful. Naturally we see 0.7 frequency of yellow morphs beca two, if it increases the yellow morphs will increase too maintains at 0.7. sistance to prion disease of different morphs in populations f yellow morphs ( compared to purple rple morphs, above and below is more or less ause that’s where the fitness is equal between the o much and fitness will drop down. So it stops and Pleiotropy -single gene affects multiple characters Closely related loci pull in different directions. Maintains variation the most - genotype x environment intera Genotypes that are advantageous action Genotypes that are advantageous You can have the case where one allele is advtangoues in on Fitness depends on genetic fitness and environment interac Example of this how different loci are advantageous on differe The girls next to us are potentially the most boring wors ne enviroment but in another ction ent flowers - maintain variation st people ever How can we explain when we have selection and varia Selection - birds born earlier in seaso - Expecting that natural selection However, laying date remains f ation but no evolution on have better survival in first winter n would leave birds being born earlier in the season fairly constant, only small decrease in laying date, but that is more to do - Expecting that natural selection However, laying date remains f with climate change Very strong selection, but no sign of evolution. High heritability and selection but no change in e path taken n would leave birds being born earlier in the season fairly constant, only small decrease in laying date, but that is more to do evolution and sometimes even opposite evolutionally How can this be explained? Biased heritability estimates Non genetic resemblances in relatives Nesting not alwasyd done close to parents, Similarity of parents and offspring declines as offspring Factoring in spatial patterns, heritability of laying date d they hatch. Clutch size however has true heritability, but laying date The chicks do their own things Here expect big birds to be selecting as they raise young be But due to countervailing selection ( bigger birds survive les dispered from parents declines as chicks are further away from where e has low affect to selection. etter ss well in wild ) its not sselected for Here expect big birds to be selecting as they raise young be But due to countervailing selection ( bigger birds survive les Can have changes year to year not just overall in a animals etter ss well in wild ) its not sselected for s life This is equation for a single trait ( breeders equation look up? ) R = h2 S. R is the response to selection, S is the selection diff heritability. This is the workhorse equation for quantitative gen This equation is with multiple traits B = The selection response to a giv With R=Gb There is a relationship in traits and is an association ) ferential, and h2 is the narrow-sense netics. n gradient shows how much an organism's relative fitness (ω) changes in ven increase or decrease in the value of a trait. n with is factored in using co variances If there is no association in two traits covariances is 0 E.g. hair colour and height don’t affect each other out However weight and height do so need to facto change if you begin to change another factor ( e Left is no relation Middle is if you select on one trait other decreases Right is if you select on one trait the other increases 0 or in co variances as the means of either factor will e.g changing height affects weight ) Left is no relation Middle is if you select on one trait other decreases Right is if you select on one trait the other increases Correlated characters pose problems E.g if selection acts on shape and size of beak, these wil af Here u want broad ( deep ) and long beak But if you take out beak depth you then want a smal ffect each other. ller beak. Thought selection was on large beaks, but was actually selec Normally selection if strong enough can break these correlatio Correlated characters - co evolution Co evolution with nectar spurs and moths tongues ( moths p evolving size of flower cting for narrow beaks on polinate the flower ) are due to each other,