parasexual cycle

parasexual cycle defined in 1951 year

parasexual cycle - parasexual cycle;
parasexual cycle - Breeding system of certain fungi (including both those with normal sexual reproduction and those with only asexual reproduction) that involves genetic recombination outside the sexual cycle. System comprises the following steps: (1) rare (1 in 106 to 107) fusion of two, genetically unlike nuclei in a heterokaryotic mycelium to produce a diploid heterozygous nucleus which (2) multiplies by mitosis during which crossing over occasionally occurs followed, again at rare intervals (1 in 103) by (3) formation of haploid nuclei from the diploids (haploidization) in which whole chromosomes reassert at random producing new genetic combinations. Starting from a culture containing a mixture of genetically different haploid nuclei the result of the parasexual cycle is a much more varied mixture of nuclei consisting of hap-loids like the originals, haploid recombinants, homozygous and heterozygous diploids. Little is yet known of natural significance of the parasexual cycle but it has already been shown to determine variation in pathogenicity in certain plant pathogens.

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