Kobayashi Kazuya, Ishizu Hirotsugu, Arioka Sachiko, Padilla Cabrera Jocelyn, Hoshi Motonori, Matsumoto Midori
Department of Biosciences and Informatics, Keio University, Hiyoshi 3-14-1, Kouhoku-ku, Yokohama 223-8522, Japan.
Chromosoma. 2008 Jun;117(3):289-96. doi: 10.1007/s00412-008-0148-6. Epub 2008 Jan 29.
Triploidy has generally been considered to be an evolutionary dead end due to problems of chromosomal pairing and segregation during meiosis. Thus, the formation of tetraploids and diploids from triploid types is a rare phenomenon. In the present study, we demonstrated that inbreeding of the triploid planarian Dugesia ryukyuensis resulted in both diploid and triploid offspring in nature. In the triploids of D. ryukyuensis, chiasmata between homologous chromosomes were observed in both female and male germ lines. This result suggests that both diploid and triploid offspring of this species are produced bisexually by zygotic fusion between sperm and eggs. Hence, this phenomenon may be a novel mechanism in planarian for escaping the triploid state.
由于减数分裂过程中染色体配对和分离的问题，三倍体通常被认为是进化的死胡同。因此，从三倍体类型形成四倍体和二倍体是一种罕见的现象。在本研究中，我们证明了三倍体日本三角涡虫的近亲繁殖在自然条件下产生了二倍体和三倍体后代。在日本三角涡虫的三倍体中，在雌性和雄性生殖系中均观察到同源染色体之间的交叉。这一结果表明，该物种的二倍体和三倍体后代都是通过精子和卵子之间的合子融合以两性方式产生的。因此，这种现象可能是三角涡虫逃避三倍体状态的一种新机制。
