Frequency increase and mitotic stabilization of a B chromosome in the fish Prochilodus lineatus.
Six populations of the fish Prochilodus lineatus were analysed for B chromosome frequency. A study of spermatogenesis revealed the absence of B accumulation during the stages analysed. In one of the populations, from the Mogi-Guaçu river where samples have been analysed over a ten-year period, B chromosome frequency doubled between 1979-80 and 1987 89, whereas no additional changes were noticed in samples collected in 1991-92. The analysis of B chromosome mitotic instability, manifested by intraindividual variation in B chromosome number, indicated a very significant decrease during this time period. This suggests that, in the 1980s, this population was in the final stage of B chromosome invasion, and that there was a possible causal relationship between B mitotic instability and the accumulation mechanism that caused its frequency increase. Mitotic stabilization might thus be a way by which a mitotically unstable B chromosome may become neutralized.
Cavallaro
Z I
ZI
Depto. de Genética e Evoluçao, Universidade Federal de São Carlos, SP, Brazil.
Bertollo
L A
LA
Perfectti
F
F
Camacho
J P
JP
D000818:Animals; D005075:Biological Evolution; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000502:physiology* / Q000648:ultrastructure; D005260:Female; D005399:Fishes / Q000235:genetics* / Q000502:physiology; D007621:Karyotyping; D008297:Male; D008540:Meiosis; D008938:Mitosis; D011110:Polymorphism, Genetic; D013090:Spermatocytes / Q000648:ultrastructure; D013091:Spermatogenesis; D013093:Spermatogonia / Q000648:ultrastructure