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Chapter 4a-5.docx

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BIOL 2000
Joseph Rasmussen

Chapter 4a-5  Negative interference – more double cross overs then expected (cross over in one region promotes cross overs in another region)  Positive interference (usually) – fewer double cross overs than expected (one cross-over region inhibits cross-over sin another region) Example  3 point test cross. Which gene is in the middle? o Progeny  ABC 450 P  abc 440 P  Abc 4 DCO  aBC 6 DCO  ABc 25 SCO (a +c)  abC 30 SCO (a+c)  aBc 25 SCO (a+b)  AbC 20 SCO (a+b) o Compare your parental and DCO groups to get middle gene. Which one switched?  A  What is A-C map distance? o = % recombinants A-C  25+30+4+6 / 1000 x 100 = 6.5 m.u  What is A-B map distance? o =% recombinants A-b  25+20+4+6/1000 x 100 – 5.5 m.u  What is the total distance? o = 6.5+5.5  12 m.u  Interference o 1- observed DCO/ expected DCO o 1- (4+6) / [(0.55)(0.065) x 1000]  Multiply individual probabilities to get expected DCO o =-1.8  Cross individual homozygous recessive at a and b to an individual homozygous recessive at c. Then test cross the resulting trihybrid. What is the probability of the abc phenotype in the progeny? o aabbCC x AABBcc  baC/baC x BAc/BAc  F1= bac/BAc o We need a cross over at a and c to get progeny of abc.  P(SCO between a and c) x p(no cross over for a and b)  6.5 map distance between a and c (needs to happen twice to get it, so half it) and multiply for the chance of the other cross over not happening o % chance is 0.055 minus from 1 to get chance of not happening  =(1/2)0.065 x (1-.055) o 0.0307 = 3% chance Example  A-B distance= 20 mu o Te
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