Early stages of sex chromosome differentiation in fish as analysed by simple repetitive DNA sequences

Abstract

Abstract. Animal sex chromosome evolution has started on different occasions with a homologous pair of autosomes leading to morphologically differentiated gonosomes. In contrast to other vertebrate classes, among fishes cytologically dernonstrahle sex chromosomes are rare. In reptiles, certain motifs of simple tandemly repeated DNA sequences like (gata)n/(gaca)m are associated with the constitutive heterochromatin of sex chromosomes. In this study a panel of simple repetitive sequence probes was hybridized to restriction enzyme digested genomic DNA of poeciliid fishes. Apparent male heterogamety previously established by genetic experiments in Poecilia reticulata (guppy) was correlated with male-specific hybridization using the (GACA) 4 probe. The (GAT A) 4 oligonucleotide identifies certain male guppies by a Y chromosomal polymorphism in the outbred population. In cantrast none of the genetically defined heterogametic situations in Xiphophorus could be verified consistently using the collection of simple repetitive sequence probes. Only individuals from particular populations produced sex-specific patterns of hybridization with (GAT A) 4 • Additional poeciliid species (P. sphenops, P. velifera) harbour different sex-specifically organized simple repeat motifs. The observed sex-specific hybridization patterns were substantiated by banding analyses of the karyotypes and by in situ hybridization using the (GACA) 4 probe.

Linkage Analysis Reveals the Independent Origin of Poeciliid Sex Chromosomes and a Case of Atypical Sex Inheritance in the Guppy (Poecilia reticulata)

“…Later, the Y-specific segment has been clearly detected at a terminal location in mitotic and meiotic spreads by chromosome in situ hybridization, comparative genomic hybridization, and synaptonemal complex analysis (Nanda et al 1992;Traut and Winking 2001). Consistent with this, predictions from our results suggest a distal location of the Y-specific segment and the Sex locus.…”

Cytogenetics of bisexual/unisexual species of Poecilia. IV. Sex chromosomes, sex chromatin composition and Ag-NOR polymorphisms in Poecilia latipinna: a population from Mexico

“…For example, males of P. reticulata appear to show XY heterogamety (Nanda et a!. 1990(Nanda et a!. , 1992.…”

Simple DNA repeats and sex chromosome differentiation in Asellus aquaticus (Crustacea, Isopoda)

“…These sequences have been implicated in a variety of functions, although they might arise by DNA replication slippage or unequal crossing-over and have no primary function. Some simple sequences are sexspecifically organized and the evolution of morphologically differentiated sex chromosomes has been associated with their significant accumulation by some researchers (for reviews see Epplen, 1988;Nanda et a!., 1992).…”

“…sequences have been observed in the heterochromosomes of snakes (Jones & Singh, 1985), rats (Schafer et at., 1986) and a poeciliid fish (Nanda et at., 1990(Nanda et at., , 1991(Nanda et at., , 1992. Other poeciliid species harbour the GGAT and CA sex-specifically organized simple repeat motifs (Nanda et a!., 1992).…”

“…Other poeciliid species harbour the GGAT and CA sex-specifically organized simple repeat motifs (Nanda et a!., 1992). Moreover, long stretches of (TCC),, simple repeats characterize bird W chromosomes (Nanda et at., 1991).…”