Abstract
Fishes exhibit the greatest diversity of species among vertebrates, offering a number of relevant models for genetic and evolutionary studies. The investigation of sex chromosome differentiation is a very active and striking research area of fish cytogenetics, as fishes represent one of the most vital model groups. Neotropical fish species show an amazing variety of sex chromosome systems, where different stages of differentiation can be found, ranging from homomorphic to highly differentiated sex chromosomes. Here, we draw attention on the impact of recent developments in molecular cytogenetic analyses that helped to elucidate many unknown questions about fish sex chromosome evolution, using excellent characiform models occurring in the Neotropical region, namely the Erythrinidae family and the Triportheus genus. While in Erythrinidae distinct XY and/or multiple XY-derived sex chromosome systems have independently evolved at least four different times, representatives of Triportheus show an opposite scenario, i.e., highly conserved ZZ/ZW system with a monophyletic origin. In both cases, recent molecular approaches, such as mapping of repetitive DNA classes, comparative genomic hybridization (CGH), and whole chromosome painting (WCP), allowed us to unmask several new features linked to the molecular composition and differentiation processes of sex chromosomes in fishes.
Highlights
For cytologically distinguishable sex chromosomes to emerge, one of the homologues needs to acquire at least two linked alleles that are advantageous to one sex only and possibly detrimental to the other [1,2]
Structure, and expression of particular genes are still rather poorly explored in fish sex determination and differentiation [35,37,38,39], relevant advances have been achieved concerning the molecular composition and differentiation process of sex chromosomes employing molecular cytogenetic procedures, such as chromosomal mapping of repetitive DNAs, comparative genomic hybridization (CGH), and whole chromosome painting (WCP) (e.g., [25,40,41,42])
We proposed the parallel evolutionG, ofjust sex chromosome systems of karyomorphs
Summary
For cytologically distinguishable sex chromosomes to emerge, one of the homologues needs to acquire at least two linked alleles that are advantageous to one sex only and possibly detrimental to the other [1,2]. Structure, and expression of particular genes are still rather poorly explored in fish sex determination and differentiation [35,37,38,39], relevant advances have been achieved concerning the molecular composition and differentiation process of sex chromosomes employing molecular cytogenetic procedures, such as chromosomal mapping of repetitive DNAs, comparative genomic hybridization (CGH), and whole chromosome painting (WCP) (e.g., [25,40,41,42]) In this sense, our present review emphasizes two alternative models to investigate the evolution of sex chromosomes among Neotropical fishes, exemplified by species from the Erythrinidae family and the Triportheus genus from the Triportheidae family. These fish groups have been our investigation systems for years, for which a considerable amount of conventional and molecular cytogenetic data show differential pathways on the differentiation process of the sex chromosomes
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