Mitotic processes which restore genome balance in Aspergillus nidulans

Journal of General Microbiology
B L Case, J A Roper

Abstract

Previous work had shown that haploid strains of Aspergillus nidulans with a duplicate chromosome segment (one in normal position, one translocated to another chromosome) were unstable at mitosis; genome balance was restored by spontaneous deletion of either duplicate segment. Diploids with an extra, translocated segment showed high instability which was confined to the excess segments; loss of one of these, usually that in translocated position, gave balanced diploid nuclei and the loss was assumed to be by deletion. This led to the proposal that high-frequency deletion was provoked by, and confined to, the excess segment. In the present work it has been shown that elimination of the translocated segment in such diploids occurs more frequently by mitotic crossing over than by deletion. Accordingly, in a more rigorous test of the possible association of excess segments and deletions, a diploid homozygous for an extra, translocated segment has been studied as mitotic crossing over in this strain could not give a balanced genome. The strain was extremely unstable and gave variants of which most had a balanced, or near-balanced, diploid genome. Some variants arose by simultaneous deletions involving both non-translocated segments; ...Continue Reading

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