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Biology 3300- Quantitative Genetics

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BIOL 3300
Theresa Burg

Biologyth300 Feb.12 , 2014 Quantitative Genetics Quantitative traits have a continuous distribution, not a discrete one. Has a mixture of genetic and environmental impacts on the genotype. Look at multiple loci. Japanese flounder: - Looking at the colored spots on their bodies - The amount of spots and intensity varies - The distribution is seen in the graph - These are continuously distributed Simon East: - 2 predictions o Unless looking at a large number of offspring in the F2 you will not observe the parental phenotype o Can recreate parental phenotype over time with selection - Selfed the offspring to get the F2 which results in a larger range. Do not see the extremes in the F2 as you see in the parents th - By the 5 generation had a range of parental phenotypes - Why was there a range of parental phenotypes to start with? o Part of the phenotype is determined by environment and multiple loci determine height of the flower Comparing a single locus to 3 loci you can see the F2 generation there are different numbers of genotypes. Increasing the number of loci, the probability of observing one of the parental phenotypes in the F2 decreases. - With one gene you have a 50/50 chance. With 3 genes you have 2/16 chance. 6 loci only 2/4000 would have parental genotypes. Identifying Loci - QTL = quantitative trait loci o Ex: loci responsible for height in humans, color in wheat - QTL mapping o Physically locating the genes o Can use markers o Need markers throughout the genome o Marker loci have nothing to do with the QTL, they are neutral o Use known location of marker to sequence candidate locus o Candidate gene is the gene we believe is to be one of the QTL’s Monkeyflowers - Mimulus cardinalis (Mc.) and M. lewisii (Ml) hybridize in lab - Pollinators o Mc pollinated by hummingbirds  Birds hover when pollinating  Red attracts the bird o Ml pollinated by bee (need landing pad)  Flowers are much larger  Bees don’t hover when pollinating - Fisher: alleles driven to fixation by natural selection have subtle effect on phenotype - Orr: some of the fixed alleles have large phenotypic effects - Used QTLs to determine the effects of different genes o Took parental species  F1 hybrids selfed  F2 o Took place in lab so environment was not a factor - Reproductive parts stick out differently for both species - In hummingbirds the pollen will stick to the head when they stick their beaks into the flower. When they reach another flower, the pollen on the head will be transferred and the flower will be pollinated - Did not find any phenotypes of the parents in the F2 hybrids - Screened 66 marker loci fixed in each species o Mc (5 loci) 11 11 11 11 11  Homozygous for allele 1 o Ml (5 loci) 22 22 22 22 22  Homozygou
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