FISH analysis of intraspecific aneuploids in Carex blepharicarpa

在苔草属的许多种中发现了种内非整倍体。由于苔草属植物的着丝粒染色体都是分散的，因此认为非整倍体很容易通过染色体的分裂或融合而产生。报道了一个连续的染色体数目，2n=26~32。睑下垂本研究对中国对虾种内非整倍体减数分裂构型进行了研究。对日本21个居群的小眼藓进行了18 S rDNA的染色体定位分析，并利用荧光原位杂交技术（FISH）对18 S rDNA进行了染色体定位.种内非整倍体的减数分裂染色体构型在减数分裂中期Ⅰ，发现7种内非整倍体，2n=26~32，几乎所有个体都观察到1 ~ 3个异形链三价体。由大、中、小染色体组成的异态三价体普遍存在。同源三价体被认为起源于未减数配子引起的染色体复制，在3个个体中发现，2n= 41，46和64。异态三价体在该物种中的高频率表明，大多数非整倍体可能是由染色体的分裂和/或融合引起的. 18 SrDNA与两个大二价体和两个中等二价体的末端区域杂交。而单价体和三价体则没有18 SrDNA信号。这些结果表明，C. Blepharapa可能是通过三价体或单价体的不均等分裂而维持在种群内的，没有18 SrRNA基因。

The intraspecific aneuploids are found in many species of the genus Carex. The aneuploids were thought to arise easily by chromosome fission or fusion, because all species of Carex have diffused centromeric chromosomes. A consecutive chromosome numbers, 2n=26～32 are reported in C. blepharicarpa. In this study, meiotic configurations of intraspecific aneuploids of C. blepharicarpa collected from 21 populations in Japan were analyzed, and chromosomal localization of 18S rDNA were determined by fluorescent in situ hybridization (FISH).1. Meiotic chromosome configurations of intraspecific aneuploidsAt meiotic metaphase I, seven kinds of intraspecific aneuploids, 2n=26～32 were found, and one to three heteromorphic chain trivalents were observed in almost all individuals. Heteromorphic trivalents comprising large, medium and small chromosomes were prevalent. Homomorhpic trivalents, which are thought to be originated from chromosome duplications caused by unreduced gametes, were found in three individuals with 2n=41,46, and 64. The high frequency of heteromorphic trivalents in this species indicates that most aneuploidy probably results from fission and/or fusion of chromosomes.2. FISH analysis of intraspecific aneuploidsThe 18S rDNA was hybridized to the terminal regions of two large and two medium bivalents. But, trivalent and univalent chromosomes had no 18S rDNA signal. These results show that the aneuploids of C. blepharicarpa probably maintained within population by unequal divisions of trivalents or univalents with no 18S rRNA gene.