A cytological description of 10 taxa in Metacnephia (Diptera: Simuliidae)

1982 ◽  
Vol 60 (11) ◽  
pp. 2852-2865 ◽  
Author(s):  
William S. Procunier
Keyword(s):  
Complex System ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Nucleolar Organizer ◽  
Sex Bias ◽  
Sex Linkage ◽  
Chromosome Differentiation ◽  
Species Association ◽  
Chromosome Maps ◽  
Sex Locus

Cytological descriptions and phylogenetic relationships are presented for 10 blackfly taxa in Metacnephia. These descriptions are given in terms of standard polytene chromosome maps based on M. pallipes. All members are male chiasmate and differ from related Cnephia by a whole arm interchange between chromosomes I and II. Sex chromosome differentiation varies from undefined changes resulting in a short, nonpairing centromeric segment in X0Y1 males of M. amphora to a complex system in M. borealis. The latter system involves Y chromosome differentiation by associated inversions and sex linkage of the nucleolar organizer (NO). Metacnephia borealis exhibits a sex bias in NO expression with excess expression in females and an apparent conversion phenomenon which dosage compensates males. The closest members of Metacnephia differ only in their sex chromosomes and share floating inversions; more distant taxa differ by fixed inversions as well as sex chromosomes. IIIS-1, IIIS-2, and IIIS-3 may be polymorphic, sex linked, or fixed in different species of the group. Nonhomology of sex chromosomes of different species, association of the sex locus and NO, and presence of an identical supernumerary block on nonhomologous chromosomes indicate a mobility phenomenon for certain loci.

Sibling species and sex chromosome differentiation in Simulium neornatipes (Diptera: Simuliidae)

1984 ◽  
Vol 26 (3) ◽  
pp. 318-325 ◽  
Author(s):  
D. G. Bedo
Keyword(s):  
Polytene Chromosome ◽  
Sibling Species ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Close Association ◽  
Chromosome Analysis ◽  
Sex Linkage ◽  
Direct Role ◽  
Chromosome Differentiation ◽  
Close Relationship

Polytene chromosome analysis of five Simulium neornatipes populations not only confirms the existence of the two sibling species, S. neornatipes 1 and 2, proposed earlier but reveals a third. S. neornatipes 3. These sibling species share a common standard polytene chromosome banding sequence which differs from the Australian S. ornatipes complex standard by five fixed inversions. The sharing of polymorphic inversions between the ornatipes and neornatipes complexes indicates their close relationship. The neornatipes species are distinguished from each other by additional fixed inversions and differentiated sex chromosomes. Extensive sex chromosome differentiation involving chromosome III has occurred in S. neornatipes 1 and 2. A period of incomplete sex-linkage allowing reassortment of inversions must have preceded the currently observed strong sex-linkage of differentiated sex chromosomes to account for the complex array of sex chromosomes found. The close association of sex chromosome differentiation with speciation in black flies is discussed in relation to appropriate speciation mechanisms. It is concluded that the rearrangements themselves have no direct role in the speciation process.Key words: sibling species, sex chromosomes, Simuliidae.

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 Cytogenetics of the neotropical flesh fly Pattonela intermutans (Diptera, Sarcophagidae)

2000 ◽  
Vol 23 (3) ◽  
pp. 563-567 ◽  
Author(s):  
Patricia Pasquali Parise-Maltempi ◽  
Rita Maria Pereira Avancini
Keyword(s):  
Sex Chromosomes ◽  
Chromosome Pair ◽  
Sex Chromosome ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
Pericentromeric Region ◽  
Flesh Fly ◽  
Fish Technique

Pattonella intermutans has 2n = 12 chromosomes including three metacentric and two submetacentric pairs of autosomes and an XX/XY sex chromosome pair. The autosomes are characterized by the presence of a C band in the pericentromeric region while sex chromosomes are totally heterochromatic. The FISH technique showed a nucleolar organizer region (NOR) in autosome IV.

Polymorphism and differentiation of rainbow trout Y chromosomes

Genome ◽  
2004 ◽  
Vol 47 (6) ◽  
pp. 1105-1113 ◽  
Author(s):  
Alicia Felip ◽  
Atushi Fujiwara ◽  
William P Young ◽  
Paul A Wheeler ◽  
Marc Noakes ◽  
...  
Keyword(s):  
Rainbow Trout ◽  
Y Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Morphological Differentiation ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Y Chromosomes ◽  
Cytogenetic Analyses ◽  
Clonal Lines ◽  
Sex Locus

Most fish species show little morphological differentiation in the sex chromosomes. We have coupled molecular and cytogenetic analyses to characterize the male-determining region of the rainbow trout (Oncorhynchus mykiss) Y chromosome. Four genetically diverse male clonal lines of this species were used for genetic and physical mapping of regions in the vicinity of the sex locus. Five markers were genetically mapped to the Y chromosome in these male lines, indicating that the sex locus was located on the same linkage group in each of the lines. We also confirmed the presence of a Y chromosome morphological polymorphism among these lines, with the Y chromosomes from two of the lines having the more common heteromorphic Y chromosome and two of the lines having Y chromosomes morphologically similar to the X chromosome. The fluorescence in situ hybridization (FISH) pattern of two probes linked to sex suggested that the sex locus is physically located on the long arm of the Y chromosome. Fishes appear to be an excellent group of organisms for studying sex chromosome evolution and differentiation in vertebrates because they show considerable variability in the mechanisms and (or) patterns involved in sex determination.Key words: sex chromosomes, sex markers, cytogenetics, rainbow trout, fish.

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 Sexually dimorphic recombination can facilitate the establishment of sexually antagonistic polymorphisms in guppies

2018 ◽  
Author(s):  
Roberta Bergero ◽  
Jim Gardner ◽  
Beth Bader ◽  
Lengxob Yong ◽  
Deborah Charlesworth
Keyword(s):  
Sex Chromosomes ◽  
Poecilia Reticulata ◽  
Common Ancestor ◽  
Sex Chromosome ◽  
Empirical Support ◽  
Male Meiosis ◽  
Sexually Dimorphic ◽  
Sex Linkage ◽  
Recombination Suppression ◽  
Males And Females

Summary/AbstractRecombination suppression between sex chromosomes is often stated to evolve in response to polymorphisms for mutations that affect fitness of males and females in opposite directions (sexually antagonistic, or SA, mutations), but direct empirical support is lacking. The sex chromosomes of the fish Poecilia reticulata (the guppy) carry SA polymorphisms, making them excellent for testing this hypothesis for the evolution of sex linkage. We resequenced genomes of male and female guppies and, unexpectedly, found that variants on the sex chromosome indicate no extensive region with fully sex-linked genotypes, though many variants show strong evidence for partial sex linkage. We present genetic mapping results that help understand the evolution of the guppy sex chromosome pair. We find very different distributions of crossing over in the two sexes, with recombination events in male meiosis detected only at the tips of the chromosomes. The guppy may exemplify a route for sex chromosome evolution in which low recombination in males, likely evolved in a common ancestor, has facilitated the establishment of sexually antagonistic polymorphisms.

scholarly journals Using conventionalF-statistics to study unconventional sex-chromosome differentiation

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3207 ◽  
Author(s):  
Nicolas Rodrigues ◽  
Christophe Dufresnes
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Rana Temporaria ◽  
Microsatellite Data ◽  
Homologous Chromosomes ◽  
Chromosome Differentiation ◽  
Population Analyses ◽  
Hyla Arborea ◽  
Frog Species ◽  
Heterogametic Sex

Species with undifferentiated sex chromosomes emerge as key organisms to understand the astonishing diversity of sex-determination systems. Whereas new genomic methods are widening opportunities to study these systems, the difficulty to separately characterize their X and Y homologous chromosomes poses limitations. Here we demonstrate that two simpleF-statistics calculated from sex-linked genotypes, namely the genetic distance (Fst) between sexes and the inbreeding coefficient (Fis) in the heterogametic sex, can be used as reliable proxies to compare sex-chromosome differentiation between populations. We correlated these metrics using published microsatellite data from two frog species (Hyla arboreaandRana temporaria), and show that they intimately relate to the overall amount of X–Y differentiation in populations. However, the fits for individual loci appear highly variable, suggesting that a dense genetic coverage will be needed for inferring fine-scale patterns of differentiation along sex-chromosomes. The applications of theseF-statistics, which implies little sampling requirement, significantly facilitate population analyses of sex-chromosomes.

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

2019 ◽  
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 ◽  
Shared Ancestry ◽  
Sex Chromosome System ◽  
Suppressed Recombination

ABSTRACTOnce recombination is halted between the X and Y chromosome, 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 variation in sex chromosome differentiation within clades. Here, we combined whole genome and transcriptome sequencing data to characterise 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 30 mya. 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 are largely homomorphic, with recombination persisting over a substantial fraction. However, the sex chromosomes in P. picta are completely non-recombining and strikingly heteromorphic. ln addition to being highly divergent, the sex chromosome system in P. picta includes a neo-sex chromosome, the result of a fusion between the ancestral sex chromosome and part of chromosome 7. Remarkably, the profound degradation of the ancestral Y chromosome in P. picta is counterbalanced by the evolution of complete dosage compensation in this species, the first such documented case in teleost fish. Our results offer important insight into the initial stages of sex chromosome evolution and dosage compensation.

Undifferentiated sex chromosomes in Mastotermes darwiniensis Froggatt (Isoptera; Mastotermitidae) and the evolution of eusociality in termites

Genome ◽  
1987 ◽  
Vol 29 (1) ◽  
pp. 76-79 ◽  
Author(s):  
D. G. Bedo
Keyword(s):  
Key Words ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Mitotic Metaphase ◽  
Evolution Of Sex ◽  
Termite Species ◽  
Chromosome Differentiation ◽  
Evolution Of Eusociality ◽  
Metaphase I

Meiosis and mitosis was studied in males of the primitive termite Mastotermes darwiniensis, which is closely related to the Dictyoptera. In mitotic metaphase cells 98 chromosomes were found with a matching 49 bivalents at metaphase I. Mastotermes darwiniensis has a largely acrocentric karyotype with no sex-linked translocation complexes, like those found in many other termite species, or other sex chromosome differentiation. These observations suggest that ancestral termites probably had karyotypes with many small chromosomes lacking sex chromosome differentiation and that there is no connection between the evolution of sex-linked translocation complexes and eusociality. Key words: sex chromosomes, Mastotermes, termites, eusociality.

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