Electric field-induced fusion was induced between Saccharomyces cerevisiae protoplasts from the ρ (-) heterozygous diploid strain 2114 and the respiratory-competent diploid strain 3441, carrying chromosomal markers. Close membrane contact between the cells of the two different strains (ratio 1:1) was achieved by dielectrophoresis in a weak inhomogeneous alternating field (about 1 kV/cm, 2 MHz). Due to dielectrophoresis pearl chains of two or more cells of the two strains are formed between the electrodes. Cell fusion was induced by application of two single square field pulses sufficiently high to induce reversible electrical breakdown in the membrane contact zone between cells within a pearl chain (about 7 to 8 kV/cm field strength and 40 Ms duration). The two subsequent pulses were applied at an interval of about 10 s.Hybrids could be isolated on selection medium in a high yield (compared with conventional fusion techniques). The hybrids were diploid, respiratory-competent and produced prototrophic spores. Thus, the fused hybrids contained only the chromosomal markers of strain 2114 and the cytoplasmic marker for respiratory competence from strain 3441; electro-fusion thus resulted mainly in plasmogamy.

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Electro‐fusion was induced between protoplasts of the respiratory‐deficient polyploid strain 93 and the respiratory‐competent haploid strain 111a auxotrophic for tryptophan and lysine. Close membrane contact was achieved by exposing the protoplasts to an inhomogeneous alternating field (about 1 kV/cm, 2 MHz). Cell fusion was observed by application of two field pulses (8 kV/cm, 40 μs duration) applied at an interval of 10 s. After transferring onto selection medium hybrids could be isolated. These hybrids were at first heterokaryons giving rise to parental type spontaneous segregants on nutritionally complete medium. After several passages on selection medium stable hybrids could be selected. Genetic analysis of these hybrids showed that recombination had taken place with partial or even complete elimination of the chromosome set. We suggest that chromosome imbalance occurs in one hybrid.

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