Polarized exclusion of bacteriophage T2 in crosses with T4

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Abstract
Four crosses were made between bacteriophages T4 and partially non-excludable T2 exr+4. Each cross was designed as a four-factor cross: in total seven pairs of homologous genes were used as markers, extending over half the circular map from the locus for adsorption specificity (h+) along the map segment for the early functions to osmotic-shock sensitivity (o).The frequencies of T2 markers recovered in the progeny show polarized exclusion: the frequencies are low for h+2 at the beginning of the map segment for the early functions and increasing to o+2. Recombination of T2 exr+4 is restricted for all loci concerned and the recombinational events are probably non-reciprocal. Restriction of sequential replication from a fixed starting point is proposed to explain polarized exclusion of T2 genes. Non-homology is dicussed in relation to restricted recombination.