van Baarlen P, van Dijk P J, Hoekstra R F, de Jong J H
Laboratory of Genetics, Wageningen University, The Netherlands.
Genome. 2000 Oct;43(5):827-35. doi: 10.1139/g00-047.
Taraxacum officinale L. (dandelion) is a vigorous weed in Europe with diploid sexual populations in the southern regions and partially overlapping populations of diploid sexuals and triploid or tetraploid apomicts in the central and northern regions. Previous studies have demonstrated unexpectedly high levels of genetic variation in the apomictic populations, suggesting the occurrence of genetic segregation in the apomicts and (or) hybridization between sexual and apomictic individuals. In this study we analysed meiosis in both sexual diploid and apomictic triploid plants to find mechanisms that could account for the high levels of genetic variation in the apomicts. Microscopic study of microsporocytes in the triploid apomicts revealed that the levels of chromosome pairing and chiasma formation at meiotic prophase I were lower than in that of the sexual diploids, but still sufficient to assume recombination between the homologues. Nomarski DIC (differential interference contrast) microscopy of optically cleared megasporocytes in the apomicts demonstrated incidental formation of tetrads, which suggests that hybridization can occur in triploid apomicts.
药用蒲公英（Taraxacum officinale L.）在欧洲是一种生命力旺盛的杂草，其在南部地区有二倍体有性种群，在中部和北部地区则有二倍体有性种群与三倍体或四倍体无融合生殖个体的部分重叠种群。先前的研究表明，无融合生殖种群中的遗传变异水平出乎意料地高，这表明无融合生殖个体中发生了遗传分离和（或）有性个体与无融合生殖个体之间的杂交。在本研究中，我们分析了有性二倍体和无融合生殖三倍体植物的减数分裂，以寻找能够解释无融合生殖个体中高遗传变异水平的机制。对三倍体无融合生殖个体中的小孢子母细胞进行显微镜研究发现，减数分裂前期I的染色体配对和交叉形成水平低于有性二倍体，但仍足以假定同源染色体之间发生了重组。对无融合生殖个体中经光学透明处理的大孢子母细胞进行诺马斯基微分干涉差显微镜观察，发现偶尔会形成四分体，这表明三倍体无融合生殖个体中可能发生杂交。
