http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

Although hybridization and introgression have been considered important in generation of plant diversity, their role in evolutionary diversification of animals remains unclear In this review, we reconsider the significance of introgressive hybridization in evolution and diversification of animals to determine if the generally negative assessment of these processes is warranted Unlike the situation for plants, hybrid animal taxa appear to be relatively rare This could, however, be due to negative attitudes toward hybridization and difficulty in detecting such forms Hybridization has been responsible for instantaneous creation of several unique complexes of polyploid and unisexual animals Allopolyploidy has allowed for diversification, whereas unisexual taxa have acted as conduits of gene exchange among related sexual species Many instances of diploid, bisexual taxa of hybrid origin have been put forward, but few have been carefully tested Changing attitudes toward hybrids and technological advances should allow for careful consideration of hypothesized hybrid taxa and will undoubtedly increase the number of known animal hybrid taxa

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The role of hybridization and introgression in the diversification of animals

Genetic, endocrine, and environmental components of sex determination and differentiation in the European sea bass (Dicentrarchus labrax L.)

Publisher Summary This chapter provides an outline of the methods used for classifying and identifying polyploid animals, followed by a discussion of proposed explanations for its relative rarity as compared to plants (where it may be near-ubiquitous). The duplication of entire genomes plays a significant role in evolution that has traditionally been reserved for plants, but in terms of ancient events, has recently expanded to include groups as diverse as yeast and vertebrates. More recent duplications of complete chromosome sets have been regarded as relatively unimportant in animal evolution. Polyploidy is often occurs only under remarkably uncommon circumstances among the metazoa and is therefore generate a curiosity than an evolutionary force in this group. The known cases of polyploid vertebrates and invertebrates are reviewed in succession, with notes about the phenotypic and evolutionary consequences interspersed throughout. It is known that polyploidy has arisen by a variety of mechanisms in a diverse array of animal taxa, covering approximately every major phylum. In part, the relatively low rate of discovery of polyploidy in animals reflects the low level of effort put into looking for it, which in turn is probably driven by the low expectation of success in finding it. In part, the relatively low rate of discovery of polyploidy in animals reflects the low level of effort put into looking for it, which in turn is probably driven by the low expectation of success in finding it.

Polyploidy in Animals

Lipid-lowering therapy in patients with renal disease

Chromosomes of Poecilia mexicana mexicana, one of the bisexual species involved in the hybrid origin of the unisexual teleost fish species P. formosa, were analyzed by several staining techniques. Sex-specific, differential heterochromatin, found in other congeneric species, was not observed in P. m. mexicana. Nucleolar organizer regions were polymorphic among individual specimens within a given population sample. A single specimen exhibiting intraindividual variability of chromosome pair 1 and a specimen with a triploid karyotype are also described.

Cytogenetics of bisexual/unisexual species of Poecilia. II. Analysis of heterochromatin and nucleolar organizer regions in Poecilia mexicana mexicana by C-banding and DAPI, quinacrine, chromomycin A3, and silver staining.

This study presents a cytogenetic analysis of the genus Dicentrarchus, represented by two species, D. labrax and D. punctatus. The karyotypes are very similar, even after staining with different techniques. Both species show 48 subtelocentric and acrocentric chromosomes, gradually decreasing in size. One pair of small size chromosomes has heteropycnotic and heteromorphtc short arms of longer size. These short arms are C- and Ag-positive, i.e. nucleolar organizer regions, NORs, are located there. Constitutive heterochromatin is also evident as a subcentromeric band on the long arms of a large chromosome pair. CMA3-staining confirms the location and the heteromorphism of NORs. DAPI and quinacrine produce homogeneous staining of chromosomes. A review of cytogenetic studies on ‘serranid’ species is also presented.

A karyotype analysis of the genus Dicentrarchus by different staining techniques

Chromosomes of the Amazon molly, Poecilia formosa, a unisexual species of hybrid origin, were investigated by C-banding, silver staining, and fluorescent staining with DAPI, quinacrine dihydrochloride, and chromomycin A3. Analysis of heterochromatin distribution indicates that chromosomes similar to the W chromosome of P. latipinna are not present in the unisexual species. Therefore, morphologically differentiated sex chromosomes do not form the basis of the unisexuality in P. formosa. The number and location of nucleolar organizer regions vary in P. formosa and do not correlate well with those of the parental species.

V. Iaselli

Papers

Cytogenetics of bisexual/unisexual species of Poecilia. II. Analysis of heterochromatin and nucleolar organizer regions in Poecilia mexicana mexicana by C-banding and DAPI, quinacrine, chromomycin A3, and silver staining.

A karyotype analysis of the genus Dicentrarchus by different staining techniques

Cytogenetics of bisexual/unisexual species of Poecilia. III. The karyotype of Poecilia formosa, a gynogenetic species of hybrid origin.