Karyotypes of side-necked turtles (Testudines: Pleurodira)

1980 ◽  
Vol 58 (5) ◽  
pp. 828-841 ◽  
Author(s):  
James J. Bull ◽  
John M. Legler
Keyword(s):  
Sex Chromosome ◽  
Ancestral Condition ◽  
Chromosome Heteromorphism

Karyotypes are presented for 13 of the 14 genera of side-necked turtles (suborder Pleurodira, families Pelomedusidae and Chelidae). Pelomedusids have low diploid numbers and few microchromosomes (2n = 26–36); the five largest chromosomes are homologous in the three genera. Chelids have high diploid numbers and many microchromosomes (2n = 50–64) and are similar in this respect to cryptodires (2n = 50–66). The pelomedusid karyotype is regarded as derived, probably from an ancestral condition like that seen in chelids. Gross karyotypic differences are slight or nil within genera and among closely related pleurodiran genera. Triploidy probably occurs in Platemys platycephala (family Chelidae) which has 96 chromosomes. No sex chromosome heteromorphism was observed.

Cytological evidence for population-specific sex chromosome heteromorphism in Palaearctic green toads (Amphibia, Anura)

2007 ◽  
Vol 32 (4) ◽  
pp. 763-768 ◽  
Author(s):  
G. Odierna ◽  
G. Aprea ◽  
T. Capriglione ◽  
S. Castellano ◽  
E. Balletto
Keyword(s):  
Sex Chromosome ◽  
Cytological Evidence ◽  
Chromosome Heteromorphism

Muller's Ratchet and the evolution of supernumerary chromosomes

Genome ◽  
1990 ◽  
Vol 33 (6) ◽  
pp. 818-824 ◽  
Author(s):  
David M. Green
Keyword(s):  
Genetic Information ◽  
Sex Chromosome ◽  
Chromosome Complement ◽  
Evolutionary Constraint ◽  
Supernumerary Chromosomes ◽  
Muller's Ratchet ◽  
Heteromorphic Sex Chromosomes ◽  
Muller’S Ratchet ◽  
Over Time ◽  
Chromosome Heteromorphism

Supernumerary chromosomes arise from portions of the normal chromosome complement through nondisjunction, fragmentation, or other mechanisms. Once present in the genome, they are subject to virtually the same genetic conditions that affect the evolutionary degeneration of heteromorphic sex chromosomes. Y or W chromosomes occur only in the presence of X or Z chromosomes, respectively, just as supernumeraries never occur except in the presence of the complete regular karyotype containing their progenitor sequences. Thus, mechanisms that can account for the evolution of sex-chromosome heteromorphism can also be invoked to explain the degeneration process of supernumerary chromosomes after their origination. Incipient supernumeraries initially have genes identical with those on progenitor chromosomes. This frees them from the evolutionary constraint of carrying nonduplicated genetic information, just as in Y and W chromosomes during early stages of sex-chromosome differentiation. The degeneration of supernumerary chromosomes may thus proceed via the mechanism of Muller's Ratchet. This hypothesis predicts that supernumerary chromosomes should lose functional loci, lose sequence homology with the regular genome, and gain heterochromatin over time, resulting in multiple heteromorphic forms of degenerate supernumeraries within and between populations, as is commonly observed.Key words: supernumerary chromosomes, B chromosomes, evolution, origin, Muller's Ratchet.

scholarly journals Karyotype characterization and ZZ/ZW sex chromosome heteromorphism in two species of the catfish genus Ancistrus Kner, 1854 (Siluriformes: Loricariidae) from the Amazon basin

2007 ◽  
Vol 5 (3) ◽  
pp. 301-306 ◽  
Author(s):  
Renildo R. de Oliveira ◽  
Eliana Feldberg ◽  
Maeda B. dos Anjos ◽  
Jansen Zuanon
Keyword(s):  
Sex Chromosomes ◽  
Amazon Basin ◽  
Sex Chromosome ◽  
Brazilian Amazon ◽  
Modal Number ◽  
Phylogenetic Relations ◽  
Karyotypic Formula ◽  
Pericentric Inversions ◽  
Acrocentric Chromosomes ◽  
Chromosome Heteromorphism

We present karyotypic characteristics and report on the occurrence of ZZ/ZW sex chromosomes in Ancistrus ranunculus (rio Xingu) and Ancistrus sp. "Piagaçu" (rio Purus), of the Brazilian Amazon. Ancistrus ranunculus has a modal number of 2n=48 chromosomes, a fundamental number (FN) of 82 for both sexes, and the karyotypic formula was 20m+8sm+6st+14a for males and 19m+9sm+6st+14a for females. Ancistrus sp. "Piagaçu" presented 2n=52 chromosomes, FN= 78 for males and FN= 79 for females. The karyotypic formula was 16m+8sm+2st+26a for males and 16m+9sm+2st+25a for females. The high number of acrocentric chromosomes in karyotype of Ancistrus sp. "Piagaçu" differs from the majority of Ancistrini genera studied so far, and may have resulted from pericentric inversions and translocations. The lower number of chromosomes in A. ranunculus indicates that centric fusions also occurred in the evolution of Ancistrus karyotypes. We conclude that karyotypic characteristics and the presence of sex chromosomes can constitute important cytotaxonomic markers to identify cryptic species of Ancistrus. However, sex chromosomes apparently arose independently within the genus and thus do not constitute a reliable character to analyze phylogenetic relations among Ancistrus species.

scholarly journals Sex Chromosome Heteromorphism and the Fast-X Effect in Poeciliids

2021 ◽  
Author(s):  
Iulia Darolti ◽  
Lydia J. M. Fong ◽  
Judith E. Mank
Keyword(s):  
X Chromosome ◽  
Sex Chromosomes ◽  
Poecilia Reticulata ◽  
Sex Chromosome ◽  
Comparative Approach ◽  
Sequence Evolution ◽  
Chromosome Differentiation ◽  
Poeciliid Fish ◽  
Sex Chromosome System ◽  
Chromosome Heteromorphism

AbstractAn accelerated rate of sequence evolution on the X chromosome compared to autosomes, known as Fast-X evolution, has been observed in a range of heteromorphic sex chromosomes. However, it remains unclear how early in the process of sex chromosome differentiation the Fast-X effect becomes detectible. Recently, we uncovered an extreme variation in sex chromosome heteromorphism across Poeciliid fish species. The common guppy, Poecilia reticulata, Endler’s guppy, P. wingei, and the swamp guppy, P. picta, appear to share the same XY system and exhibit a remarkable range of heteromorphism. The sex chromosome system is absent in recent outgroups, including P. latipinna and Gambusia holbrooki. We combined analyses of sequence divergence and polymorphism data across Poeciliids to investigate X chromosome evolution as a function of hemizygosity and reveal the causes for Fast-X effects. Consistent with the extent of Y degeneration in each species, we detect higher rates of divergence on the X relative to autosomes and a strong Fast-X effect in P. picta, while no change in the rate of evolution of X-linked relative to autosomal genes in P. reticulata. In P. wingei, the species with intermediate sex chromosome differentiation, we see an increase in the rate of nonsynonymous substitutions on the older stratum of divergence only. We also use our comparative approach to test different models for the origin of the sex chromosomes in this clade. Taken together, our study reveals an important role of hemizygosity in Fast-X and suggests a single, recent origin of the sex chromosome system in this clade.

Does differential selection on the 5S rDNA explain why the rainbow trout sex chromosome heteromorphism is not linked to the SEX locus?

2004 ◽  
Vol 105 (1) ◽  
pp. 122-125 ◽  
Author(s):  
R.B. Phillips ◽  
M.A. Noakes ◽  
M. Morasch ◽  
A. Felip ◽  
G.H. Thorgaard
Keyword(s):  
Rainbow Trout ◽  
Sex Chromosome ◽  
5S Rdna ◽  
Differential Selection ◽  
Chromosome Heteromorphism

Evidence for a highly differentiated sex chromosome heteromorphism in the salamander Necturus maculosus (Rafinesque)

Chromosoma ◽  
1980 ◽  
Vol 77 (2) ◽  
pp. 157-168 ◽  
Author(s):  
Stanley K. Sessions
Keyword(s):  
Sex Chromosome ◽  
Necturus Maculosus ◽  
Chromosome Heteromorphism

Meiotic recombination in the ZW pair of a tinamid bird shows a differential pattern compared with neognaths

Genome ◽  
2005 ◽  
Vol 48 (2) ◽  
pp. 286-290 ◽  
Author(s):  
M I Pigozzi ◽  
A J Solari
Keyword(s):  
Sex Chromosomes ◽  
Meiotic Recombination ◽  
Sex Chromosome ◽  
Significant Part ◽  
Pseudoautosomal Region ◽  
W Chromosome ◽  
Additional Step ◽  
Differential Pattern ◽  
Terminal Heterochromatin ◽  
Chromosome Heteromorphism

The tinamid bird Nothura maculosa, along with other species of the order Tinamiformes and all of the existent ratites, form the infraclass Paleognathae, the most primitive living birds. Previous work has shown that in all studied Neognathae, the ZW pair shows strictly localized recombination in a very short pseudoautosomal region, while in paleognath birds, the ZW pairs have mostly free recombination. The present observations show that the ZW pair of N. maculosa has a recombination pattern departing from both neognaths and other Paleognath birds, as there is a single crossover but occurring at random points along a significant part of the long arm of the W chromosome. This recombination pattern agrees with the presence of intercalary and terminal heterochromatin in the W chromosome, suggesting an exceptional, additional step of recombination suppression.Key words: recombination, ZW pair, avian sex chromosomes, sex chromosome heteromorphism.

scholarly journals Unraveling the Sex Chromosome Heteromorphism of the Paradoxical Frog Pseudis tocantins

PLoS ONE ◽  
2016 ◽  
Vol 11 (5) ◽  
pp. e0156176 ◽  
Author(s):  
Kaleb Pretto Gatto ◽  
Carmen Silvia Busin ◽  
Luciana Bolsoni Lourenço
Keyword(s):  
Sex Chromosome ◽  
Chromosome Heteromorphism

scholarly journals Chromosome Studies in Hypoptopomatinae (Pisces, siluriformes, Loricariidae): I. XX/XY Sex Chromosome Heteromorphism in Pseudotocinclus tietensis.

CYTOLOGIA ◽  
1992 ◽  
Vol 57 (3) ◽  
pp. 369-372 ◽  
Author(s):  
Artur Antonio Andreata ◽  
Lurdes Foresti de Almeida-Toledo ◽  
Claudio Oliveira ◽  
Silvio de Almeida Toledo Filho
Keyword(s):  
Sex Chromosome ◽  
Chromosome Heteromorphism
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