Mapping the Genome:
Finding the location of genes in any organism’s genome is a very
complex task. This section surveys approaches to mapping the
bacterial genome, using E.coli as an example. All three modes of
gene transfer and recombination have been used in mapping.
Hfr conjugation is frequently used to map the relative location of bacterial genes. This technique rests on the observation that during conjugation the linear chromosome moves from donor to recipient at a constant rate. In an interrupted mating experiment the conjugation bridge is broken and Hfr F mating is stopped at various intervals after the start of conjugation by mixing the culture vigorously in a blender. The order and timing of gene transfer can be determined because they are a direct reflection of the order of genes on the bacterial chromosome. For example, extrapolation of the curves in figure back to the x-axis will give the time at which
each gene just began …