Bertollo L A, Mestriner C A
Departamento de Genética e Evolução, Universidade Federal de São Carlos, SP, Brazil.
Chromosome Res. 1998 Feb;6(2):141-7. doi: 10.1023/a:1009243114124.
The neotropical fish Hoplias malabaricus shows diversified cytotypes and may represent a group of distinct species. One of these cytotypes is characterized by 2n = 40 and 2n = 39 chromosomes in females and males, respectively, with a multiple sex chromosome system of the X1X1X2X2/X1X2Y type. The Y, representing a large chromosome in male karyotype, is derived from a translocation event between two biarmed chromosomes: one of them similar to X1 chromosome (no. 6) and another one similar to X2 chromosome (probably no. 20). Meiotic data (standard and synaptonemal complexes analyses) show 18 bivalents and one characteristic trivalent in pachytene and metaphase I spermatocytes, as well as two kinds of metaphase II cells with 19 and 20 chromosomes. The trivalent is formed by the Y, X1 and X2 chromosomes and usually presents a complete pairing in pachytene. However, trivalents with partially or fully asynapsed segments are also observed. These segments are assumed to be non-homologous regions of the X1 and X2 chromosomes without correspondence with the Y chromosome, which can heterosynapse. This behaviour of the sex trivalent leading to a fully paired structure, taken together with the close frequencies of the two spermatocyte types at metaphase II, suggests a normal pattern for male H. malabaricus meiosis, representing a stabilized multiple sex chromosome system in this species.
新热带鱼马拉巴锯脂鲤表现出多样化的细胞型，可能代表一组不同的物种。其中一种细胞型的特征是，雌性和雄性的染色体数目分别为2n = 40和2n = 39，具有X1X1X2X2/X1X2Y型的多重性染色体系统。Y染色体在雄性核型中是一条大染色体，它源自两条双臂染色体之间的易位事件：其中一条类似于X1染色体（第6号），另一条类似于X2染色体（可能是第20号）。减数分裂数据（标准分析和联会复合体分析）显示，粗线期和中期I精母细胞中有18个二价体和一个特征性的三价体，以及两种中期II细胞，其染色体数目分别为19条和20条。三价体由Y、X1和X2染色体组成，在粗线期通常呈现完全配对。然而，也观察到部分或完全不联会片段的三价体。这些片段被认为是X1和X2染色体的非同源区域，与Y染色体没有对应关系，它们可以异源联会。性三价体的这种行为导致形成完全配对的结构，再加上中期II时两种精母细胞类型的频率相近，表明马拉巴锯脂鲤雄性减数分裂模式正常，代表了该物种中一个稳定的多重性染色体系统。
