一种全为雌性的鞭尾蜥物种（由有不同性别的种之间的杂交形成）的存在自1962年以来就已为人们所知了，但它是怎样用一整套体细胞染色体组来产生成熟卵的却仍不清楚，同样其维持遗传多样性的机制也不清楚。据Nature 3月11日最新报道，Lutes等人发现，在该物种中，减数分裂开始时的染色体数量是有不同性别物种的两倍，而且配对和重组发生在遗传相同的姐妹染色体之间，而不是发生在同源染色体之间。

原文出处：
Nature vol.464 (7286), (11 Mar 2010)  doi:10.1038/nature08818

Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards
Aracely A. Lutes1,2, William B. Neaves1,3, Diana P. Baumann1, Winfried Wiegraebe1 & Peter Baumann1,2,4

1 Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
2 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
3 University of Missouri Kansas City, School of Medicine, Kansas City, Missouri 64110, USA
4 Howard Hughes Medical Institute, Kansas City, Missouri 64110, USA

Although bisexual reproduction has proven to be highly successful, parthenogenetic all-female populations occur frequently in certain taxa, including the whiptail lizards of the genus Aspidoscelis. Allozyme analysis revealed a high degree of fixed heterozygosity in these parthenogenetic species1, 2, supporting the view that they originated from hybridization events between related sexual species. It has remained unclear how the meiotic program is altered to produce diploid eggs while maintaining heterozygosity. Here we show that meiosis commences with twice the number of chromosomes in parthenogenetic versus sexual species, a mechanism that provides the basis for generating gametes with unreduced chromosome content without fundamental deviation from the classic meiotic program. Our observation of synaptonemal complexes and chiasmata demonstrate that a typical meiotic program occurs and that heterozygosity is not maintained by bypassing recombination. Instead, fluorescent in situ hybridization probes that distinguish between homologues reveal that bivalents form between sister chromosomes, the genetically identical products of the first of two premeiotic replication cycles. Sister chromosome pairing provides a mechanism for the maintenance of heterozygosity, which is critical for offsetting the reduced fitness associated with the lack of genetic diversity in parthenogenetic species.