A High Frequency of Heterozygous Diploids and Somatic Recombination produced by Ultra-violet Light in Imperfect Fungi


PONTECORVO and his co-workers1 have demonstrated that, by the use of appropriate selection techniques, heterozygous diploids can be secured from heterocaryons of Aspergillus nidulans. Further, these diploids produced, on cultivation, recombinants by both somatic crossing-over2 and somatic reduction. Later, similar results were obtained with the asexual strains, Aspergillus niger 3 and Penicillium chrysogenum 4. I have succeeded in producing heterozygous diploids in the asexual fungi A. sojae and A. oryzae by the use of similar methods. These diploids also showed somatic segregation and yielded recombinations of the original genotypes. First-order segregations showed further segregation upon cultivation. Only a few segregants have been analysed and all proved to be still diploid in having double the haploid amount of deoxyribonucleic acid per nucleus. Their occurrence can be explained by the same type of somatic crossing-over as that discussed by Pontecorvo5 and originally discovered by Stern6.

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  1. 1

    Pontecorvo, G. and Roper, J. A., “Advances in Genetics”, 5, 218 (1953).

  2. 2

    Roper, J. A., and Pritchard, R. H., Nature, 175, 639 (1955).

  3. 3

    Pontecorvo, G., Roper, J. A., and Forbes, E., J. Gen. Microbiol., 8, 198 (1953).

  4. 4

    Pontecorvo, G., and Sermonti, G., J. Gen. Microbiol., 11, 94 (1954). Sermonti, G., Rend. 1st. Sup. Sanità, 17, 231 (1954).

  5. 5

    Pontecorvo, G., Caryologia, Vol. Supp. 1 (1954).

  6. 6

    Stern, C., Genetics, 21, 624 (1936).

  7. 7

    James, A. P., Genetics, 40, 204, 826 (1955).

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