Favarato Ramon M, Braga Ribeiro Leila, Ota Rafaela P, Nakayama Celeste M, Feldberg Eliana
Cytogenet Genome Res. 2019;158(1):38-45. doi: 10.1159/000499954. Epub 2019 May 11.
Karyotypes and chromosomal characteristics with focus on B chromosomes of 2 species of the serrasalmid genus Metynnis, namely M. lippincottianus and M. maculatus, were examined using conventional (C-banding) and molecular (FISH mapping of minor and major rDNAs and Rex1, Rex3, and Rex6 retrotransposable elements) protocols. Both species possessed a diploid chromosome number of 2n = 62 and karyotypes composed of 32 metacentric + 28 submetacentric + 2 subtelocentric and 32 metacentric + 26 submetacentric + 4 subtelocentric, respectively; one small B element was found in the female genome of M. lippincottianus. C-banding revealed heterochromatin in the pericentromeric and terminal portions of all chromosomes of both species; the B chromosome was entirely heterochromatic. FISH showed 18S rDNA sites in 2 chromosome pairs in both species (pairs 19 and 22), and a large block in the B chromosome, while 5S rDNA signals were detected in the first pair of subtelocentric chromosomes in both species, moreover in M. maculatus an additional labeled pair 4 was observed. Mapping of the Rex1, Rex3, and Rex6 retrotransposable elements in the genomes of M. lippincottianus and M. maculatus indicated that they were dispersed throughout nearly all the chromosomes of the complement, except for the B chromosome of M. lippincottianus.
利用传统方法（C带）和分子方法（小rDNA和大rDNA以及Rex1、Rex3和Rex6反转录转座元件的荧光原位杂交图谱），对锯脂鲤科的两个物种，即利氏锯脂鲤（Metynnis lippincottianus）和斑锯脂鲤（Metynnis maculatus）的核型和染色体特征进行了研究，重点关注B染色体。两个物种的二倍体染色体数均为2n = 62，核型分别由32条中着丝粒染色体 + 28条亚中着丝粒染色体 + 2条近端着丝粒染色体和32条中着丝粒染色体 + 26条亚中着丝粒染色体 + 4条近端着丝粒染色体组成；在利氏锯脂鲤的雌性基因组中发现了一个小的B染色体。C带显示两个物种所有染色体的着丝粒周围和末端部分均有异染色质；B染色体完全是异染色质。荧光原位杂交显示两个物种在两对染色体（第19对和第22对）中有18S rDNA位点，在B染色体中有一个大的区域，而在两个物种的第一对近端着丝粒染色体中均检测到5S rDNA信号，此外，在斑锯脂鲤中还观察到另外一对标记的第4对染色体。利氏锯脂鲤和斑锯脂鲤基因组中Rex1、Rex3和Rex6反转录转座元件的图谱表明，它们几乎分散在整个染色体组中，除了利氏锯脂鲤的B染色体。
