Andreata A A, do Almeida-Toledo L, Oliveira C, Toledo Filho S de A
Departamento de Biologia, Instituto de Biociências, USP, Brazil.
Cytogenet Cell Genet. 1993;63(4):215-20. doi: 10.1159/000133538.
Cytogenetic analysis of two local populations of Microlepidogaster leucofrenatus showed a basic diploid chromosome number (2N) of 54 in both populations. Some fishes were found to have a 2N = 55 or 56 chromosomes due to the presence of one or two large heterochromatic B chromosomes. Specimens of M. leucofrenatus from the Poço Grande stream had 24 metacentrics, 24 submetacentrics, four subtelocentrics, and one submetacentric homomorphic pair in males and one submetacentric/subtelocentric heteromorphic pair in females, whereas individuals of this species from the Marumbi River had 22 metacentrics, 24 submetacentrics, four subtelocentrics, two acrocentrics, and one submetacentric/subtelocentric heteromorphic pair in females. The occurrence of the heteromorphic pair in the females was due to the presence of an extra C-banded segment on the W chromosome. Ag-NORs in both populations were located interstitially on the short arm of the largest metacentric pair. The Poço Grande population had less constitutive heterochromatin than did the Marumbi River population. The speciation process in this fish species is discussed on the basis of heterochromatin distribution.
对两个本地白鳍小鳞脂鲤种群的细胞遗传学分析表明，两个种群的基本二倍体染色体数（2N）均为54。由于存在一条或两条大型异染色质B染色体，发现一些鱼的染色体数为2N = 55或56。来自波苏格兰德溪流的白鳍小鳞脂鲤标本，雄性有24条中着丝粒染色体、24条亚中着丝粒染色体、4条近端着丝粒染色体和一对亚中着丝粒同形染色体，雌性有一对亚中着丝粒/近端着丝粒异形染色体；而来自马伦比河的该物种个体，雌性有22条中着丝粒染色体、24条亚中着丝粒染色体、4条近端着丝粒染色体、2条端着丝粒染色体和一对亚中着丝粒/近端着丝粒异形染色体。雌性中异形染色体对的出现是由于W染色体上存在一个额外的C带区段。两个种群的银染核仁组织区均位于最大中着丝粒对的短臂中间位置。波苏格兰德种群的组成型异染色质比马伦比河种群少。基于异染色质分布对该鱼类物种的物种形成过程进行了讨论。
