Ro_Lecture6

Ro_Lecture6 - Lecture 6 A geneticist isolates two...

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1 Lecture 6 A geneticist isolates two mutations: ŝ A = tall ŝ a = short ŝ H = hairy ŝ h = no hair and constructs the following pure-breeding stocks: AAhh and aaHH. These individuals are mated and the F1 progeny are mated to the double recessive. The following results are obtained in the F2: Do these genes reside on the same or different chromosomes? Answer- Same- linked If they reside on the same chromosome, what is the distance between them? We simply must identify the parental and recombinant classes and determine the recombinant frequency #Recombinants/Total progeny
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2 P AAhh x aaHH A h x a H A h a H F1 AaHh x aahh A h x a h a H a h Parental Recomb
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3 Which are the parental and which are the recombinant classes? What is the recombination frequency? So the map distance between the A and H genes is 410+415 825 =29% 410+1007+987+415 2819
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4 Another mutation C (crinkled) is isolated and recombination frequencies between this gene and the A and H genes are determined % recombinants A to H 29 A to C 15 H to C 16 A H C 29 15 16 15+16=31 not 29
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5 What is going on? The map is not internally consistent? ---A-------H------------------ ---A-------H------------------ ---a-------h------------------ ---a-------h------------------ A-H parental A-h Recomb a-H Recomb a-h parental ---A--------------------H----- ---A--------------------H----- ---a--------------------h----- ---a--------------------h----- A-H parental A-H parental a-h parental a-h parental Single cross-over Double cross-over The parental class is over counted for progeny with 2 crossovers The recombinant class is under counted for the progeny with two crossovers Over large distance there will be a significant number of double crossovers that go undetected:
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6 The double crossovers go undetected and therefore over large distances the genetic distances are underestimated The solution is to include intervening markers to greatly reduce the probability of undetected doubles:
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Ro_Lecture6 - Lecture 6 A geneticist isolates two...

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