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11.7.07 - Darren Rothberg Biol 105 Evolution 11.7.07 1...

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Darren Rothberg Biol 105 – Evolution 11.7.07 1) Selection on Quantitative Traits a Directional selection (i) Selection against individuals at one end of the phenotype distribution in favor of individuals at the other extreme Rabbits in Australia 1859: 24 British rabbits introduced to an estate in Victoria, Australia (S.W. Australia) 1928: throughout heritable areas of Australia 500 million in an area of 1 million square miles Severe damage to grazing lands (sheep) Kangaroo and other native grazers equally hurt 1950: inoculated with Myxomatosis virus 1953: 95% of the rabbits killed Outcomes Rabbits more resistant to the virus Only resistant rabbits to survive & reproduce Virus less virulent Only less virulent forms transmitted Only these forms survive and reproduce Co-evolution : the rabbits and the virus evolved in response to one another Candidate locus BMP4: signaling molecule that helps shape beaks of other bird species mRNA expression indicated by dark staining One QTL contributing to beak size variation (ii) Directional selection occurs when Environmental changes New beneficial mutation appears If directional selection persists Genetic variation will be depleted Ultimately limiting response to selection b Stabilizing selection (i) Selection against both extremes of the phenotype distribution (ii) In favor of intermediate phenotypes (iii) Long considered the typical condition in stable environments Karn and Penrose (1951):
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Stabilizing selection on human birth weight Stabilizing selection on a gall-forming fly, Eurosta solidaginis Female injects egg into bud of a tall goldenrod ( Solidago altissima ) After hatching, larva digs into stem Induces gall formation Gall protects larva Two Problems: Female parasitoid wasp can inject egg in gall where wasp will develop and eat fly larva
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