In an Hfr (Pyr+; Met+. Xyl+, Tyr+, Arg+, His+ or Mal+) X F- (Pyr-; Met-. Xyl-, T

Question

In an Hfr (Pyr+; Met+. Xyl+, Tyr+, Arg+, His+ or Mal+) X F- (Pyr-; Met-. Xyl-, Tyr-, Arg-, His- or Mal-) cross, the recipient cells become Pyr+ in 5 minutes, but at this time point there are no recipient cells that are Met+. Xyl+, Tyr+, Arg+, His+ or Mal+. The mating is now allowed to proceed for a longer period of time and Pyr+ recipient cells are selected. Of the Pyr+ cells, 32% are Met+, 94% are Xyl+, 7% are Tyr+, 59% are Arg+, 0% are His+ and 71% are Mal+. What can you conclude about the order of the genes on the chromosome? Draw a simple map of the Hfr strains chromosome to indicate the location of the F plasmid relative to the other genes.

Explanation / Answer

The gene which enters first will exhibit higher rate of recombination and act as origin where the fertility factors would get inserted into the recipient cell.   The increasing order of the percentage of recombination frequency would indirectly indicate that order of genes on the chromosome was His (Terminal or last to enter)

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