Maintenance of Heterozygosity in a Homothallic Species of the Neurospora tetrasperma Type

Abstract

IN the homothallic ascomycete Neurospora tetrasperma, two nuclei are normally included in each ascospore, one of mating type A and one of mating type a. N. tetrasperma is therefore normally a dikaryon and heterozygous for the Aa factors. It is interesting to note that the inclusion of an A and an a nucleus in one ascospore leads to the maintenance of heterozygosity of other factors not on the same chromosome but segregating at the same time as the Aa factors. A factor segregates at the first meiotic division if there has been no crossing-over between the factor and the centromere of the chromosome on which it is placed. If there has been such crossing-over the factor segregates at the second division. A factor placed about fifty crossover units from the centromere would be expected to show 100 percent second division segregation, apart from the effect of double cross-overs.

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    Dodge, B. O., Schmitt, B. Mary, and Appel, Anita, Proc. Amer. Phil. Soc., 89 4, 575 (1945).

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SANSOME, E. Maintenance of Heterozygosity in a Homothallic Species of the Neurospora tetrasperma Type. Nature 157, 484–485 (1946) doi:10.1038/157484c0

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