Explanation of the HIS4-TRP1example in Monday’s (2-5-07)lectureWhat if two crossovers?T. SlabyHISHIStrptrphishisTRPTRPX XHIShistrpTRPHIShistrpTRP2 X-oversOn diffchromosMeiosis I (homologsSeparate)HIShistrpTRPHIShistrpTRPHIShistrpTRPHIShistrpTRPMeiosis IISistersSeparatePossible combos of these allelesHIS trphis TRPHIS TRPhis trpORHIS trphis TRPHIS TRPhis trpORPairing each of these mutuallyexclusive possibilities results inHIS TRP his trpHIS TRP his trpHIS trp HIS TRPhis TRP his trpHIS trp HIS trphis TRP his TRPNPDPDTTRatios121parentalsnonparentalsparentals nonparentalsRecombination event‘tween CENx and his4only‘tween CENx and his4And‘tween CENy and trp1Tetrad pattern that results100% chance of Tetratype (TT)50% chance of a TT25% chance of a NPD25% chance of a PDIf you dissect 100 tetrads and all only recombined between CENx and his4 and not CENy and trp1 then you’d have 100Tetratypes, or 200 recombinants. (100x2 = 200)If you dissect 100 tetrads and all had both recombination events then you’d have 50 TT, 25 NPD, and 25 PD; or 200 recombinants.(50x2 + 25x4 = 200)Thus for the purpose of determining if two genes are linked it makes no difference how far away each is fromits chromosome’s centromere.If you wanted to estimate how far away the his4 locusis from its chromosome’s centromere? Would it matter if trp1is tightly linked to its chromosome’s centromere? How so?(hint: trp1 is tightly linked to its centromere)Why would researchers find using Neurospora easier than S. cerevisiae (baker’s yeast) for mapping mutations relative to a centromere?Summary and Question(s) for the
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