A CONSIDERATION OF THE NEGATIVE CORRELATION BETWEEN TRANSMISSION RATIO AND RECOMBINATION FREQUENCY IN A MALE RECOMBINATION SYSTEM OF DROSOPHILA MELANOGASTER

Abstract

The negative correlation between transmission ratio (k) and male recombination frequency (.theta.), which was found in the presence of the major male recombination element (Mr) in the pr+ region of the T-007 chromosome, was examined for hypothesized minor male recombination elements associated with T-007. Many minor male recombination elements are distributed along the arms of the T-007 chromosome. They generally cause a reduction in k and an increase in .theta., and their expression seems to be constant among males within each line. The presence of another type of male recombination element is also suggested. An Mr-related mutational change (analogous to paramutation) seems to occur in the pr region (therefore, the Mr+ region) of previously non-male recombination 2nd chromosomes. This change, designated Mr'', enables those chromosomes which carry it to induce some male recombination and a distorted transmission ratio. The expression of Mr'' seems to vary among males with each line. The relationship between k and .theta. among males within the same line is supposedly related to the position of the elements in the chromosome. Specifically, minor elements, which locate in largely euchromatic regions of the chromosome, appear to be stable in their expression, while the Mr and Mr'' elements, which locate in or adjacent to the centric heterochromatin, appear to be unstable. The expression of these elements may be variable among males within each line such that the activities of Mr of Mr'' are stronger (lower k, higher .theta.) for some males, while they are weaker (higher k, lower .theta.) for other males. The rate of the Mr-related mutational change, Mr+ .fwdarw. Mr'', is approximately 0.50.