PS2C - BICD100 Genetics Winter 2008 Problem Set 2C!...

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Problem Set 2C Bacterial Genetics 1. In the cross Hfr ilv+ bgl+ mtl+ x F- ilv- bgl- mtl- , it is known that ilv is transferred later than bgl or mtl . However the relative order of bgl and mtl is not known. You cross the two strains as above and select for Ilv+ exconjugants. You screen these colonies for Bgl and Mtl phenotypes. You obtain the following results: Genotype number of colonies 1. Ilv+Bgl+Mtl+ 222 2. Ilv+Mtl-Bgl- 60 3. Ilv+Mtl+Bgl- 0 4. Ilv+Mtl-Bgl+ 18 Draw a map of the three genes showing their order and distances in % recombination. The order is given by the rarest (indeed nonexistent) class, which is Ilv+Mtl+Bgl-. This tells us bgl is in the middle. A Ilv+Bgl-Mtl+ exconjugant can only arise by a quadruple crossover. [In an exam problem you may be required to infer which class is missing. ..] Class I has transferred all 3 genes and had no crossovers between them Crossover between Ilv and Bgl gives class 2. So ilv bgl map distance is 60/300 = 20% recombination. Crossover between Bgl and Mtl gives class 4.
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This note was uploaded on 06/07/2008 for the course BICD 100 taught by Professor Nehring during the Winter '08 term at UCSD.

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PS2C - BICD100 Genetics Winter 2008 Problem Set 2C!...

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