Altiero Tiziana, Rebecchi Lorena
Department of Animal Biology, University of Modena and Reggio Emilia, Modena, Italy.
Hereditas. 2003;139(2):116-20. doi: 10.1111/j.1601-5223.2003.01719.x.
Chromosome behaviour during male meioses has been studied in two bisexual amphimictic populations of two tardigrade species, namely Richtersius coronifer and Macrobiotus richtersi (Eutardigrada, Macrobiotidae). Both bisexual populations exhibit a diploid chromosome number 2n=12 and no sex chromosomes were identified. DAPI staining and C-banding data indicate that all chromosomes of the bisexual population of R. coronifer are acrocentric. In both species, at male meiotic prophase, all six bivalent homologous chromosomes are aligned side by side along their length and show no evidence of chiasmata. However, in the oocytes of both species a chiasma is generally present in each bivalent at diplotene stage. Lack of recombination is previously unknown in tardigrades, but is a well known phenomenon in many other metazoans where it is always restricted to the heterogametic sex. In tardigrades there is no evidence of heterochromosomes, but it does not mean that in tardigrades, the heterogametic sex does not exist. The adaptive and evolutionary significance of achiasmatic meiosis is discussed.
在缓步动物门的两个物种，即王冠鳞隐棘虫（Richtersius coronifer）和里氏大生熊虫（Macrobiotus richtersi）（真缓步纲，大生熊虫科）的两个两性有性生殖种群中，对雄性减数分裂过程中的染色体行为进行了研究。这两个两性种群的二倍体染色体数目均为2n = 12，且未鉴定出性染色体。4,6-二脒基-2-苯基吲哚（DAPI）染色和C带数据表明，王冠鳞隐棘虫两性种群的所有染色体均为近端着丝粒染色体。在这两个物种中，雄性减数分裂前期，所有六条二价同源染色体沿其长度并排排列，未显示交叉现象。然而，在这两个物种的卵母细胞中，在双线期每个二价体通常都存在一个交叉。在缓步动物中，缺乏重组现象此前未知，但在许多其他后生动物中是一种众所周知的现象，在这些动物中，重组总是局限于异配性别。在缓步动物中没有异染色体的证据，但这并不意味着在缓步动物中不存在异配性别。本文讨论了无交叉减数分裂的适应性和进化意义。
