Study on mechanism of obtaining genetic diversity in agaposermous plants

无精子是一种不通过配子受精而产生新的后代个体的生殖系统。在植物中，除了营养生殖外，还经常发现无精子生殖。在无胚植物中，既不会发生多样化，也不会发生遗传变化，因为它们是与母本植物相同的克隆体。因此，它被称为进化的死胡同。然而，大量的遗传变异往往出现在无精子植物群体中。摘要本研究旨在阐明菊科两属蒲公英（Taraxacum，日本二倍体蒲公英与T.officinale杂交）和Ixeris （Ixeris dentata complex）无精子植物获得遗传多样性的机制。本研究对无精子种群和有性种群的染色体数目进行了分析，并对其遗传变异进行了研究，旨在阐明无精子种群获得遗传多样性的机制。摘要对蒲公英和伊克斯兰两种植物种群进行了野生种群遗传分析、杂交实验和二倍体有性种、三倍体和四倍体无精子种的生态生理特征分析。在这两个属中，在野生种群中观察到遗传变异。尤其在伊塞里斯人群体中，大多数个体之间存在不同的基因型，这与前人的研究结果一致。为了阐明遗传多态性产生的机制，对三倍体无性种与二倍体有性种、二倍体有性种与推定杂交种、三倍体无性种与两属的个体进行了杂交实验。结果，在每个检测组合中都获得了杂种。对杂交所得种子进行进一步分析，并用流式细胞仪测定蒲公英的DNA含量。结果，获得了F1杂交种与二倍体或其他杂交种个体杂交的证据。少

Agamospermy is a reproductive system that produces a new descendant individual without fertilization of the gametes. In plants, agamospermy is often found in addition to vegetative reproduction. In agamospermy, neither the diversification nor the genetic changes take place because they are the same clone to their mother plant. Thus, it was said as the blind alley of evolution. However, large amount of the genetic variation are often found in agamospermous plant population. The purpose of this study is to clarify the mechanism that agamospermous species acquires genetic diversity by using two genera of Asteraceae, Taraxacum (hybridization between the Japan diploid dandelions and T.officinale) and Ixeris (Ixeris dentata complex). In this study, agamospermous and sexual population was analyzed in chromosome number, the genetic variation were examined for the purpose of clarification of mechanisms to obtain genetic diversity in agamospermous species.In the populations of Taraxacum and Ixer … More is, the genetic analyses of wild populations, crossing experiments, ecological and physiological characteristics in diploid sexual species, and triploid and tetraploid agamospermous species. In both genera, genetic variation was observed in the wild population examined. Especially in the Ixeris, most individuals in the population were found to be having different genotype one another, and it was concordant with previous studies. To clarify a mechanism to produce genetic polymorphism, crossing experiments was done between individuals of triploid asexual species and diploid sexual species, diploid sexual species and presumed hybrids, and the individuals of triploid asexual species in both genera. As a result, hybrids were obtained in every combination examined. The seeds obtained by crossing experiment were analyzed further, for DNA content with a flow cytometer were done in Taraxacum. As a result, the evidence that the F1 hybrids had been crossing with the diploids or the other hybrid individual was obtained. Less