Lect 20 - Office hour TODAY, 11-noon 2214 Natural Sciences...

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©2003 C. Brachmann 1 Gene Mapping Bio Sci 97 Lecture 20 Dr. Carrie Brachmann Department of Developmental and Cell Biology cbrachma@uci.edu Office hour TODAY, 11-noon 2214 Natural Sciences I
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©2003 C. Brachmann 2 Outline Double Cross-overs Three-point Testcross Interference
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©2003 C. Brachmann 3 Expanding the genetic map: the  linkage group pr vg 11cM add the gene light:  the recessive  allele, lt, and vg have a rec freq of  10%; pr and lt have a rec freq of 1%   vg lt 10cM 1cM pr lt !! Rec freq’s (and therefore map  distances) between loci are  additive!!   vg lt pr pr lt vg OR and so on and so on and so on…
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©2003 C. Brachmann 4 A linkage group corresponds to one  chromosome pair. values in map units Fig from Modern Genetic Analysis W.H Freeman and Co, publ
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©2003 C. Brachmann 5 0.0 roughoid eyes 100.7 claret eyes 100.7 map units If the recombination frequency between two loci cannot exceed 50%, how are these two genes mapped 100.7 map units apart???
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©2003 C. Brachmann 6 ©2000 Lee Bardwell What is the best map of the three genes? ab/ab x AB/ab: 35% AB 15% Ab 16% aB 34% ab ad/ad x AD/ad: 29% AD 20% Ad 22% aD 29% ad bd/bd x BD/bd: 25% BD 25% Bd 25% bD 25% bd Given:
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©2003 C. Brachmann 7 For each cross: 1. identify the recombinant classes 2. add the rec freq’s for the recombinant classes = map  distance in m.u. or cM The two shorter distances should be additive and equal the  longer distance, roughly   ab/ab x AB/ab: 35% AB 15% Ab 16% aB 34% ab ad/ad x AD/ad: 29% AD 20% Ad 22% aD 29% ad bd/bd x BD/bd: 25% BD 25% Bd 25% bD 25% bd Given:
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©2003 C. Brachmann 8 A D B 42 cM 31 cM B 31 cM A 42 cM D but, B and D are  unlinked?? They are on the same chromosome ~ 73cM ab/ab x AB/ab: 35% AB 15% Ab 16% aB 34% ab ad/ad x AD/ad: 29% AD 20% Ad 22% aD 29% ad bd/bd x BD/bd: 25% BD 25% Bd 25% bD 25% bd Given:
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©2003 C. Brachmann 9 ab/ab x AB/ab: 43.1% AB 8.5% Ab 6.2% aB 42.2% ab ad/ad x AD/ad: 46.6% AD 5.0% Ad 5.7% aD 42.7% ad bd/bd x BD/bd: 38.9% BD 10.4% Bd 13.4% bD 37.3% bd Let’s try this one: ©2000 Lee Bardwell What is the best map of the three genes?
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©2003 C. Brachmann 10 A B D 14.7 cM 10.7 cM D 10.7 cM A 14.7 cM B but, 25.4 > 23.8 obs ab/ab x AB/ab: 43.1% AB 8.5% Ab 6.2% aB 42.2% ab ad/ad x AD/ad: 46.6% AD 5.0% Ad 5.7% aD 42.7% ad bd/bd x BD/bd: 38.9% BD 10.4% Bd 13.4% bD 37.3% bd
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©2003 C. Brachmann 11 Fig 4.8 Genetecists cannot detect all crossover events:  double crossovers double crossover leads to exchange of a  segment  of the chromosomes, but the  marker genes  are not recombined,  thus the map distance is  UNDERESTIMATED **no double crossovers over  short distances (~10% rec freq)
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©2003 C. Brachmann 12 Mapping pitfalls double crossovers lead to
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Lect 20 - Office hour TODAY, 11-noon 2214 Natural Sciences...

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