FISH analysis of intraspecific aneuploids in Carex blepharicarpa

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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.