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.

The pattern of sex chromosome kinetochore phosphorylation during nonrandom segregation in a flea beetle

2000 ◽  
Vol 78 (2) ◽  
pp. 93-98
Author(s):  
Holly Kupfer ◽  
Dwayne Wise
Keyword(s):  
Key Words ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Flea Beetle ◽  
Beetle Species ◽  
Kinetochore Protein ◽  
Linear Configuration ◽  
Meiosis I ◽  
Metaphase I

In the flea beetle species, Alagoasa bicolor, males have two sex chromosomes, X and Y, each of which is larger than the rest of the genome combined. These large sex chromosomes do not pair at meiosis I, and are therefore not joined at metaphase I. Nevertheless, they always segregate from each other at anaphase I. As prometaphase I progresses, the unpaired X and Y undergo reorientation from a parallel to a linear configuration. Using 3F3/2, an antibody that detects the level of phosphorylation of a kinetochore protein or proteins, we have determined that this reorientation is not accompanied by a change in the level of phosphorylation of the kinetochores of either X or Y. This implies that: i) either the reorientation does not involve the loss or gain of kinetochore microtubules, or ii) if such loss or gain occurs, it does not effect a change in the tension placed on the nonrandomly segregating kinetochores, or iii) the sex chromosomes, as in some other species, have lost the ability to sense kinetochore tension changes. Evolution of nonrandom segregation may necessitate the inability of the participating chromosomes to affect the metaphase checkpoint. Key words: nonrandom segregation, sex chromosomes, kinetochores.

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 Meiotic Behavior of Achiasmate Sex Chromosomes in the African Pygmy Mouse Mus mattheyi Offers New Insights into the Evolution of Sex Chromosome Pairing and Segregation in Mammals

Genes ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1434
Author(s):  
Ana Gil-Fernández ◽  
Marta Ribagorda ◽  
Marta Martín-Ruiz ◽  
Pablo López-Jiménez ◽  
Tamara Laguna ◽  
...  
Keyword(s):  
Dna Repair ◽  
Y Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Mammalian Species ◽  
Evolutionary Process ◽  
Small Region ◽  
Pseudoautosomal Region ◽  
Evolution Of Sex ◽  
African Pygmy Mouse

X and Y chromosomes in mammals are different in size and gene content due to an evolutionary process of differentiation and degeneration of the Y chromosome. Nevertheless, these chromosomes usually share a small region of homology, the pseudoautosomal region (PAR), which allows them to perform a partial synapsis and undergo reciprocal recombination during meiosis, which ensures their segregation. However, in some mammalian species the PAR has been lost, which challenges the pairing and segregation of sex chromosomes in meiosis. The African pygmy mouse Mus mattheyi shows completely differentiated sex chromosomes, representing an uncommon evolutionary situation among mouse species. We have performed a detailed analysis of the location of proteins involved in synaptonemal complex assembly (SYCP3), recombination (RPA, RAD51 and MLH1) and sex chromosome inactivation (γH2AX) in this species. We found that neither synapsis nor chiasmata are found between sex chromosomes and their pairing is notably delayed compared to autosomes. Interestingly, the Y chromosome only incorporates RPA and RAD51 in a reduced fraction of spermatocytes, indicating a particular DNA repair dynamic on this chromosome. The analysis of segregation revealed that sex chromosomes are associated until metaphase-I just by a chromatin contact. Unexpectedly, both sex chromosomes remain labelled with γH2AX during first meiotic division. This chromatin contact is probably enough to maintain sex chromosome association up to anaphase-I and, therefore, could be relevant to ensure their reductional segregation. The results presented suggest that the regulation of both DNA repair and epigenetic modifications in the sex chromosomes can have a great impact on the divergence of sex chromosomes and their proper transmission, widening our understanding on the relationship between meiosis and the evolution of sex chromosomes in mammals.

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.

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 Sex chromosome configurations in pachytene spermatocytes of an XYY mouse

1990 ◽  
Vol 56 (2-3) ◽  
pp. 129-133 ◽  
Author(s):  
Charles Tease
Keyword(s):  
Sex Chromosomes ◽  
Male Mouse ◽  
Sex Chromosome ◽  
Chromosome Constitution ◽  
Sterile Male ◽  
Xy Bivalent ◽  
Pachytene Spermatocytes ◽  
Metaphase I

SummaryKaryotypic investigation of a phenotypically normal but sterile male mouse showed the presence of an XYY sex chromosome constitution. The synaptic behaviour of the three sex chromosomes was examined in 65 pachytene cells. The sex chromosomes formed a variety of synaptic configurations: an XYY trivalent (40%); an XY bivalent and Y univalent (38·5%); an X univalent and YY bivalent (13·8%); or X, Y, Y univalence (7·7%). There was considerable variation in the extent of synapsis and some of the associations clearly involved nonhomologous pairing. These observations have been compared with previously published information on chromosome configurations at metaphase I from other XYY males.

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.

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.

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