Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes).
Chromosomes of a species of Eigenmannia presenting a X1X1X2X2:X1X2Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A3 (CMA3) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA3/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G + C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought.
Departamento de Biologia, Universidade de São Paulo, Brazil. lftoledo@usp.br
L F
LF
Almeida-Toledo
F
F
Foresti
M F
MF
Daniel
S A
SA
Toledo-Filho
D000818:Animals; D005075:Biological Evolution; D014128:Chromomycin A3 / Q000737:chemistry; D004555:Electric Fish / Q000235:genetics*; D005260:Female; D006570:Heterochromatin; D007621:Karyotyping; D008297:Male; D008926:Plicamycin / Q000737:chemistry; D015183:Restriction Mapping; D012730:Sex Chromosomes / Q000235:genetics*; D012733:Sex Differentiation; D016622:Silver Staining / Q000379:methods; D014178:Translocation, Genetic
D006570:Heterochromatin; D014128:Chromomycin A3; D008926:Plicamycin