Mechanisms and Genetic Implications of 2n-Gamete Formation
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1984-05
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Abstract
Gametes with the unreduced number (= 2h) of chromosomes may originate from different abnormal events during meiosis or arise in apomeiotic somatic ceils of the ovule (apospory). Meiotic nuclear restitution leading to 2n-gamet.es may be associated with fused or parallel second metaphase spindles (First Division Restitution, FDR) or with incomplete second meiotic division (Second Division Restitution, SDR). Its association with failing or reduced homologous pairing leads to 2n-gametes which are genetically equivalent to FDR. The basic differences between FDR and SDR are described and explained. Several mechanisms of 2n-gamete formation occurring in association with failing or reduced homologous pairing, as they occur in megaspore mother cells of apomictic species and in spore mother cells of synaptic mutants, interspecific hybrids, amphimonoploids, and anortho-ploids, are described and discussed. Different mechanisms of 2n-gamete production are compared as to their genetic implications. Data about genetic control of processes leading to 2n-gametes are presented along with a discussion on the effects of environmental factors on occurrence and frequency of 2n-gametes. Index Descriptors: nuclear restitution, 2n-gametes, dyads, apomixis, synaptic mutants, premeiotic doubling, autobivalents, fused spindles, endomitosis, and apospory.
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Iowa State Journal of Research, May 1984, Vol.58 No.4