Pairing interaction as a basis for negative interference

Abstract

The recurring problem of negative interference in conjugal crosses ofEscherichia coliK-12 (Rothfels, 1952; Cavalli-Sforza & Jinks, 1956; Wollman, Jacob & Hayes, 1956) has been periodically overshadowed by new discoveries concerning the mechanism of genetic transfer in this organism, such as unidirectional and partial transfer (Hayes, 1953; Wollmanet al., 1956) and the genetic heterogeneity of zygotes formed in F+× F−crosses (Jacob & Wollman, 1957), which have led to reappraisal of the interpretation of the genetic data. While some of those data (e.g. those of Rothfels, 1952) can be interpreted entirely on the basis of prezygotic elimination of the male genetic contribution, others (e.g. those of Cavalli-Sforza & Jinks, 1956) could not be, and were not, explained entirely on such a basis but demanded the introduction of the notion of incomplete pairing. Meanwhile the problem of negative interference became an important issue in other microorganisms such as bacteriophage,Aspergillus, Neurosporaand yeast (review, Pritchard, 1960). The most plausible current model of localized negative interference in these organisms postulates that chromosome pairing is discontinuous and random, and that recombination only occurs within those small regions where pairing is effective (Pritchard, 1955; Chase & Doermann, 1958); thus the ‘coincidence of recombination in two intervals would occur with greater than random frequency if these intervals were short enough and close enough to be frequently included within one effectively paired segment’ (Pritchard, 1960). The mean distance over which such negative interference operates is very small, being of the order of only a few cistrons in both bacteriophage andAspergillus(Pritchard, 1960).