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BIOC16H3 (11)
Lecture 8

BIOC16 Lecture 8.pdf

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Biological Sciences
Mark Fitzpatrick

BIOC16 Lecture 8 Correlations among traits When you notice that the larger individuals have lighter fur than the smaller individuals so why are these two traits correlated?! - to now we've been dealing with single phenotypic traits! - method to understand genetics and evolution of a group of traits simultaneously! Beetle! ! Weight ! Elytra! ! Flight wings Elytra length Why or how are traits correlated?! - pleiotropic effects: one locus affects more than one trait! Eg: morning glory ( ipomoea purpurea) Simmons and Bucher 1996! ! W- floral pigments! 50% dead! WW -dark! Ww - light! 50% dead ! ww - white! 61% dead W locus has pleiotropic effects on floral color and toxicity! ! 1) pleiotropy! 2) linkage! ! Consider 2 genes A and B - each has 2 alleles A1A2 and B1B2! ! p1 f(A1). q (B1)! p2 f(A2) q(B2)! When the random association isn't observed we call it linkage disequilibrium! - physical linkage! - but physical linkage isn't essential! ! Recombination! -mixing of maternal and paternal genes into new combinations in offsprings! Two instances: 1) meiosis- prophase 1- chromosomes pairing up! - crossing over! 2) random probability that the maternal or paternal chromosomes of each homologous pair line up on either side of metaphase plate.! ! If two loci are unlinked (ie. different chromosomes) the probability of recombination between them is 0.5 ( highest amount of recombination and this number decreases as things become more linked)! If these loci are sufficiently close together ( same chromosome, same arm of chromosome)... They are linked. The probability of recombination between them is now proportional to the physical distance between them. No crossing over - Far apart or on right next to each different chromosomes other ( or same gene) Rate determining how fast a population in linkage disequilibrium (LD) reaches linkage equilibrium (LE) What causes LD?! 1) selection for particular combinations of alleles! 2) mixture of 2 populations with different allele frequencies! 3) random genetic drift! ! Eg: heterostyly in English Primrose ( primula vulgaris)! ! Two genes Gg - style length - shank is dominant! Aa - anther position - high is dominant! ! Morphs! "Pin" - long style and anthers ! are well below stigma! Stigma! Style! ! Anthers ! "Thrum"- short style, stigma is ! midway, anthers high! ! ! ! Homostyle Genes for style length and anther position are in LD! - selection against selfing Quantitative Trait Locus Mapping Case study - lab working on mice and they are interested in longevity - how do you find genes for longevity - you can use knock out however your mutations will result in drastic changes. Looking for subtle evolutionary changes you take a different approach.! ! First step is to ask - does there appear to be variability in the trait of interest? So you see that there is
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