Summary
A mutation (rec) confering low mitotic recombination in a haploid of Aspergillus nidulans carrying the duplication I pab y adE8 bi +/IIdy y + adE20 bi was tested for its effect on mitotic recombination in diploids and on meiosis. The method involved the building of strains that on mating in pairwise combinations can give heterokaryons and diploids homozygous for different sets of chromosomes coming from the rec strain. Three such diploids were tested so far, in which no effect on recombination frequency was found; it means that if rec affects diploids it is not located on linkage groups III, IV, V, or VII. The strains for building the other diploids have been constructed. The construction of a diploid homozygous for linkage group I from the rec parent required a transfer of the duplicated segment y + adE20 bi from chromosome II to its original place on chromosome I. A method for this transfer involving two-step selection is described.
A mutation (pop) confering very high mitotic-recombination frequency was found to have a profound effect on crossing over in diploids: all the asexual spores show at least one crossing-over event. The high recombination could be due to the effect of pop on chromosome exchange per se, or on chromosome pairing and thus indirectly on exchange. A test designed to support the second hypothesis failed to supply this support. Since there are other results supporting the first hypothesis it is concluded that pop has a direct effect on mitotic crossing over. The possible uses of pop mutants for mitotic genetic mapping, and for testing whether mitotic crossing over is a special case of sister-strand exchange, are discussed.
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Parag, Y. Genetic analysis of mutations for low (rec) and very high (pop) mitotic-recombination frequency in Aspergillus nidulans . Molec. Gen. Genet. 155, 319–327 (1977). https://doi.org/10.1007/BF00272812
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DOI: https://doi.org/10.1007/BF00272812