Genome 371 Lecture 12 - Genome 371 Lecture 12 1/26/11 4:17...

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1/26/11 4:17 PM Genome 371 Lecture 12 Page 1 of 12 http://courses.washington.edu/au371mkr/resources/lecture_notes/lecture_12.html Lecture 12 Genetic mapping-2 12 Nov 2010 Lecture 12 handout (pdf) Notes on hybridization (pdf) Subscribe to podcast: Slide 1 Slide 2 Home Course mechanics Help hours Calendar Syllabus Lectures, Podcasts Quiz Sections Practice problems Exams GoPost Send email to class Useful links The Gradiator
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1/26/11 4:17 PM Genome 371 Lecture 12 Page 2 of 12 http://courses.washington.edu/au371mkr/resources/lecture_notes/lecture_12.html Slide 3 Slide 4 A note on the notation: the A and B loci are not shown linked (i.e., the genotype is written with a broken line between the two loci) because we don't know whether these two loci are linked or not. Slide 5 Since the recombination machinery makes crossovers at random locations* along the length of the chromosome, it follows that genes that are far apart on a chromosome are more likely to have a crossover between them than genes that are close together. Furthermore, the probability of recombination between genes should be a measure of how far apart they are. *Fine print: there are actually "hotspots" and "cold spots" with for recombination, but on average, and for our purposes, the location of crossovers can be considered to be random. Also, recombination rates differ even between males and females in humans, being higher in females than in males. Slide 6 So, by measuring the percent recombinant progeny from a testcross, we can deduce the relative distances between genes. Let's look at a case where A/a , B/b , and D/d are all on the same chromosome. If a testcross gives 20% recombinant products with respect to A/a and B/b , but only 5% recombinant products between B/b and D/d , we would conclude that the distance between A/a and B/b must be about 4- fold greater than the distance between B/b and D/d . Additivity of map distances breaks down when the distances are large, as we'll see.
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1/26/11 4:17 PM Genome 371 Lecture 12 Page 3 of 12 http://courses.washington.edu/au371mkr/resources/lecture_notes/lecture_12.html Slide 7 Slide 8 Slide 9
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1/26/11 4:17 PM Genome 371 Lecture 12 Page 4 of 12 http://courses.washington.edu/au371mkr/resources/lecture_notes/lecture_12.html Slide 10 Slide 11 We cannot look directly at how many crossovers are occurring between a pair of genes. (It's actually possible to do so by molecular means in some instances, if we know where to look, but if we knew where the genes were, we wouldn't need to do these experiments in the first place.) So, we can either. .. 1. look at the genotypes of gametes produced by meiosis if possible (e.g., looking at the haploid products of meiosis in yeast); 2. or infer the gamete genotypes by allowing those gametes to fertilize and produce progeny, and then based on the progeny phenotypes figure out what the gamete genotypes must have been (as we saw with pr vg etc.) Either way, by calculating the % of recombinant gametes, we can calculate map distance. The
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This note was uploaded on 03/31/2011 for the course GENOME 371 taught by Professor Unsure during the Spring '03 term at University of Washington.

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Genome 371 Lecture 12 - Genome 371 Lecture 12 1/26/11 4:17...

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