biol139-lecture20-2011

Pick any two genes to start with rf is always a

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Unformatted text preview: of a pair of genes Example: • Lets look at the distance between y-w Parentals were yw and y+w+ Recombinants: should be yw+ and y+w We do not care if flies are ec or ec+ at this point F2 Male Phenotype Male y w ec y+ w+ ec+ Observed Numbers 4685 y 4759 y + w+ 70 y w+ e c + 207 3 y+ w ec+ ec ec+ parentals Recombinants: should be yw+ and y+w 80 193 y+ w+ ec w Map distance between y-w, is y-w calculated as % recombinants. Do this by summing all offspring with recombinant phenotype and dividing by total # of progeny (10,000) multiplied by 100: 3 10,000 70 + 80 + 3 + 3 x 100 = 1.56 m.u 1.56 10,000 Repeat for each pair Distance between w - ec Distance 207 + 193 + 3 + 3 x 100 = 4.06 m.u 4.06 10,000 Distance between y - ec 5.50 m.u. Distance 5.50 Construct the map 1.56 m.u y w 4.06 m.u ec 5.5 m.u Notice the distance separating outside genes does not add up WHY?? F2 Construct the map Male Male Phenotype y w ec y+ w+ ec+ y w+ ec+ 1.56 m.u y Observed Numbers 4685 4759 4.06 m.u ec 5.5 m.u Parental class will be the two with the highest frequency. All others are recombinants Next two highest (after most distance genes) will 70 be single crossovers between two closest genes 80 (Region 1) y 193 y+ w+ ec w 207 w ec Next two highest frequencies (after parentals) will be single crossover recombinants between the two most distance genes (Region 2) 3 y+ w ec+ 3 10,000 Two with the least frequency are double crossovers This method allows correction for double crossovers double Heterozygous female y w ec y+ w+ ec+ y+ w ec y w+ ec+ Region1 Parentals NCO y+ w+ y w Region1 Single cross over with respect to y SCO Region 1 y w ec+ y+ w+ ec Single cross over with respect to ec SCO Region 2 y w+ ec y+ w ec+ Double cross over with respect to w DCO Regions 1+2 Region2 y+ y X 70 + 80 ec w+ y+ w+ y w Region1 y+ y X 3 Region2 w Region1 ec+ w+ w ec+ ec Region2 X 193 + 207 Region2 X 3 ec+ ec ec+ ec Correction for distance between y and ec The distance of 5.5 m.u. between y and ec does not account for 5.5 between double crossovers. Does not reflect ALL recombination events ALL that produce y...
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