GENE20001 Lecture Notes - Lecture 18: Trp Operon, Fine Structure, Centimorgan
Document Summary
Putting colonies on minimal selects for trp+ cys+ The cotransduction frequency, which is a measure of genetic distance between these two markers, is the proportion of cys+ cells that are also trp+ For the cys and trp genes the cotransduction frequency was found to be 0. 5. Transduction can be used to determine the order of genes and measure the relative distances between them. This allows mapping of genes within a 5 minute segment of the e. coli chromosome. Generalised transduction can be used for fine structure mapping. Mutations within a gene can be mapped relative to an outside marker, eg. the cys gene can be used to map mutations within the trp gene with respect to cys and each other. We want to see whether trpa or trpb is closer to cys. To do this a pair of (cid:862)reciprocal(cid:863) crosses is set up usi(cid:374)g two trp (cid:373)uta(cid:374)ts (trpa- and trpb-).
