• Journal of The Korean Society of Grassland and Forage Science
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• v.17 no.1
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• pp.1-10
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• 1997

Unreduced (2n) gametes are meiotic products (pollen or egg) having a sporophytic (somatic) chromosome number, resulting from abnormalities during either microsporogenesis or megasporogenesis. They occur naturally at a low frequency in many plant species. Unreduced (2n) gametes in plants can be identified for four possible ways as follow i) pollen size and/or shape differences between haploid (n) and diploid (2n) pollen, ii) ploidy analysis (chromosome number) of progeny or meiotic analysis (presence of dyads andlor triads at the microspore stage), iii) progeny performance and fertility and iv) dosage of isozyme and DNA markers. Unreduced (2n) gametes can be an effective breeding tool in synthesizing new cultivars, providing a unique method to maximizing heterozygosity, i.e., transferring a large proportion of the non-additive genetic effects (intra- and inter- locus interactions) h m parent to offspring and can also be used to overcome infertility of interploidy crosses. Sexual polyploidization through 2n gametes has been a major route to the formation of naturally occurring polyploids. The three mechanisms of 2n pollen formation in potato have been discovered as follow: i) parallel spindles (ps) or tripolar spindles (ts), ii) premature cytokinesis (pc-I, pc-2) and iii) synaptic mutants (sy-2, sy-3, sy-4). Genetic analysis indicated that the mechanisms of 2n gamete formation were controlled by single recessive gene in potato, alfalfa, red clover, etc., and by two recessive genes in wheat. The use of 2n gametes which can efficiently transfer germplasm fiom wild relatives to cultivated species, especially fiom diploid to tetraploid could make a contribution to the improvement of germplasm base in breeding programs.

• Korean Journal of Plant Taxonomy
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• v.32 no.4
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• pp.467-480
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• 2002

The development of the female gametophyte of Corydalis albipetala, C. ambigua, C. filistipes, C. nobilis, C. solida, C. ophiocarpa have been comparatively investigated using laser scanning confocal microscope (LSCM) and light microscope. An archesporium was originated from one of the outmost parietal cells beneath the one-layered epidermis of protuberant nucellus, and acted directly as a megaspore mother cell (MMC). These species had linear tetrads after successional meiotic division during the megasprogenesis. A functional megasprore developed from one of the tetrad in the chalazal end, and the rest three being degenerated. The developmental type of the female gametophyte was monosporic in accordance with the Polygonum type. Prior to anthesis the female gametophyte was organized. So mature embryo sac was comprised a three-celled egg apparatus, three large antipodals were developed from the apex of each antipodal cell, and extended toward micropylar end to be contacted with egg apparatus. Two synergids were usually observed as degenerated condition, and in this time the apices of antipodal haustoria were connected with the degenerated synergids. The developmental characteristics of seven-nucleate female gametophytes were common in all the species investigated. But the shape of mature embryo sac was ovoidal in C. albipetala, C. filistipes, C. ophiocarpa and C. solida, reflexed in C. ambigua, and rather flattened ovoidal in C. nobilis. Also, the type of megasporangium was anatropous in all the species except C. ambigua with campylotropous ovule.