An early stage of ZW/ZZ sex chromosome differentiation in Poecilia sphenops var. melanistica (Poeciliidae, Cyprinodontiformes)

Chromosoma ◽  
1984 ◽  
Vol 89 (1) ◽  
pp. 37-41 ◽  
Author(s):  
T. Haaf ◽  
M. Schmid
Keyword(s):  
Sex Chromosome ◽  
Early Stage ◽  
Chromosome Differentiation ◽  
Poecilia Sphenops

SEX CHROMOSOME DIFFERENTIATION: AN INTERMEDIATE STAGE IN A LIZARD

1978 ◽  
Vol 20 (2) ◽  
pp. 205-209 ◽  
Author(s):  
James Bull
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Early Stage ◽  
Intermediate Stage ◽  
Meiotic Cell ◽  
Chromosome Differentiation ◽  
Cell Divisions ◽  
Staining Techniques

Sex chromosomes of the lizard, Cnemidophorus tigris (Baird and Girard), were analyzed in mitotic and meiotic cell divisions using C-band and G-band staining techniques. The X and Y are homologous along most of their lengths but do not crossover in the medial portion of the bivalent, where their centromeres lie. In this region the X and Y differ in centric position and heterochromatin. The similarities of the X and Y in C. tigris contrast to sex chromosomes in other animals, and probably represent an early stage of differentiation.

scholarly journals Telomere-to-telomere assembly of a fish Y chromosome reveals the origin of a young sex chromosome pair

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Lingzhan Xue ◽  
Yu Gao ◽  
Meiying Wu ◽  
Tian Tian ◽  
Haiping Fan ◽  
...  
Keyword(s):  
Y Chromosome ◽  
Sex Chromosomes ◽  
Chromosome Pair ◽  
Sex Chromosome ◽  
Structural Variations ◽  
Recombination Suppression ◽  
Chromosome Differentiation ◽  
Y Chromosomes ◽  
Recent Origin ◽  
Mastacembelus Armatus

Abstract Background The origin of sex chromosomes requires the establishment of recombination suppression between the proto-sex chromosomes. In many fish species, the sex chromosome pair is homomorphic with a recent origin, providing species for studying how and why recombination suppression evolved in the initial stages of sex chromosome differentiation, but this requires accurate sequence assembly of the X and Y (or Z and W) chromosomes, which may be difficult if they are recently diverged. Results Here we produce a haplotype-resolved genome assembly of zig-zag eel (Mastacembelus armatus), an aquaculture fish, at the chromosomal scale. The diploid assembly is nearly gap-free, and in most chromosomes, we resolve the centromeric and subtelomeric heterochromatic sequences. In particular, the Y chromosome, including its highly repetitive short arm, has zero gaps. Using resequencing data, we identify a ~7 Mb fully sex-linked region (SLR), spanning the sex chromosome centromere and almost entirely embedded in the pericentromeric heterochromatin. The SLRs on the X and Y chromosomes are almost identical in sequence and gene content, but both are repetitive and heterochromatic, consistent with zero or low recombination. We further identify an HMG-domain containing gene HMGN6 in the SLR as a candidate sex-determining gene that is expressed at the onset of testis development. Conclusions Our study supports the idea that preexisting regions of low recombination, such as pericentromeric regions, can give rise to SLR in the absence of structural variations between the proto-sex chromosomes.

scholarly journals Sex chromosome differentiation in Belostoma (Insecta: Heteroptera: Belostomatidae)

2012 ◽  
Vol 11 (3) ◽  
pp. 2476-2486 ◽  
Author(s):  
V.B. Bardella ◽  
A.L. Dias ◽  
L. Giuliano-Caetano ◽  
J.R.I. Ribeiro ◽  
R. da Rosa
Keyword(s):  
Sex Chromosome ◽  
Chromosome Differentiation

scholarly journals Extreme heterogeneity in sex chromosome differentiation and dosage compensation in livebearers

2019 ◽  
Vol 116 (38) ◽  
pp. 19031-19036 ◽  
Author(s):  
Iulia Darolti ◽  
Alison E. Wright ◽  
Benjamin A. Sandkam ◽  
Jake Morris ◽  
Natasha I. Bloch ◽  
...  
Keyword(s):  
Y Chromosome ◽  
Dosage Compensation ◽  
Sex Chromosomes ◽  
Poecilia Reticulata ◽  
Sex Chromosome ◽  
Sequencing Data ◽  
Chromosome Differentiation ◽  
Y Chromosomes ◽  
Shared Ancestry ◽  
Suppressed Recombination

Once recombination is halted between the X and Y chromosomes, sex chromosomes begin to differentiate and transition to heteromorphism. While there is a remarkable variation across clades in the degree of sex chromosome divergence, far less is known about the variation in sex chromosome differentiation within clades. Here, we combined whole-genome and transcriptome sequencing data to characterize the structure and conservation of sex chromosome systems across Poeciliidae, the livebearing clade that includes guppies. We found that the Poecilia reticulata XY system is much older than previously thought, being shared not only with its sister species, Poecilia wingei, but also with Poecilia picta, which diverged roughly 20 million years ago. Despite the shared ancestry, we uncovered an extreme heterogeneity across these species in the proportion of the sex chromosome with suppressed recombination, and the degree of Y chromosome decay. The sex chromosomes in P. reticulata and P. wingei are largely homomorphic, with recombination in the former persisting over a substantial fraction. However, the sex chromosomes in P. picta are completely nonrecombining and strikingly heteromorphic. Remarkably, the profound degradation of the ancestral Y chromosome in P. picta is counterbalanced by the evolution of functional chromosome-wide dosage compensation in this species, which has not been previously observed in teleost fish. Our results offer important insight into the initial stages of sex chromosome evolution and dosage compensation.

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

Chromosoma ◽  
1992 ◽  
Vol 101 (5-6) ◽  
pp. 301-310 ◽  
Author(s):  
Indrajit Nanda ◽  
Manfred Schartl ◽  
Wolfgang Feichtinger ◽  
J�rg T. Epplen ◽  
Michael Schmid
Keyword(s):  
Repetitive Dna ◽  
Dna Sequences ◽  
Sex Chromosome ◽  
Repetitive Dna Sequences ◽  
Chromosome Differentiation ◽  
Early Stages
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