a1 Botany Department, University of St. Andrews, Queen's College, Dundee
Genetic recombination through the parasexual cycle, or some very similar system, was demonstrated. Diploid strains were very unstable, yielding about 95% haploid conidia from three-week-old cultures This high frequency of haploid segregants was at least partly attributable to greater sporulation of haploid mycelium, but may also reflect a higher frequency of haploidization than that found in Aspergillus nidulans.
Mitotic crossing-over also occurred frequently, and gave segregants homozygous for some markers but heterozygous for others. It was also detectable by changes in the phase of linked markers occurring during vegetative growth. Some heterozygous segregants were either aneuploids, or were formed by double mitotic crossovers.
Haploid segregants, derived from nuclei which had previously undergone mitotic crossing-over, were often recovered. This coincidence of mitotic crossing-over and haploidization in one nuclear lineage, together with the probable occurrence of double mitotic crossovers, makes mitotic analysis less clear cut than in Aspergillus nidulans.
(Received January 25 1964)