GATA repeats in the genome of Asellus aquaticus (Crustacea,Isopoda)

A 500 bp fragment of Drosophila genomic DNA containing 37 copies of the tetranucleotide GATA was used to probe, by Southern DNA blotting and in situ hybridization, two natural populations of the isopod crustacean Asellus aquaticus collected from the Sarno and Tiber rivers. This species does not have a recognizable sex chromosome pair. In a number of males from the Sarno population chromomycin A₃ staining reveals a heteromorphic chromosome pair. The heterochromosome has two blocks of heterochromatin. After digestion of genomic DNA with six restriction endonucleases and hybridization with the GATA probe, the two populations exhibit different fragment length patterns. No sex-linked pattern was observed in either population. In situ hybridization to chromosomes of males and females from the Sarno population does not reveal any sex-specific pattern of labelling and indicates a scattered distribution of GATA sequences on most chromosomes with some areas of preferential concentration. The heterochromatic arcas of the male heterochromosome are not labelled.by E.R. Schmidt     

Evolution of karyotype,sex chromosomes,and meiosis in mygalomorph spiders (Araneae: Mygalomorphae)

Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X₁X₂0, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 377–408.     

Geographic variation in sex‐chromosome differentiation in the common frog (Rana temporaria)

In sharp contrast with birds and mammals, sex‐determination systems in ectothermic vertebrates are often highly dynamic and sometimes multifactorial. Both environmental and genetic effects have been documented in common frogs (Rana temporaria). One genetic linkage group, mapping to the largest pair of chromosomes and harbouring the candidate sex‐determining gene Dmrt1, associates with sex in several populations throughout Europe, but association varies both within and among populations. Here, we show that sex association at this linkage group differs among populations along a 1500‐km transect across Sweden. Genetic differentiation between sexes is strongest (F_ST = 0.152) in a northern‐boreal population, where male‐specific alleles and heterozygote excesses (F_IS = ?0.418 in males, +0.025 in females) testify to a male‐heterogametic system and lack of X‐Y recombination. In the southernmost population (nemoral climate), in contrast, sexes share the same alleles at the same frequencies (F_ST = 0.007 between sexes), suggesting unrestricted recombination. Other populations show intermediate levels of sex differentiation, with males falling in two categories: some cluster with females, while others display male‐specific Y haplotypes. This polymorphism may result from differences between populations in the patterns of X‐Y recombination, co‐option of an alternative sex‐chromosome pair, or a mixed sex‐determination system where maleness is controlled either by genes or by environment depending on populations or families. We propose approaches to test among these alternative models, to disentangle the effects of climate and phylogeography on the latitudinal trend, and to sort out how this polymorphism relates to the ‘sexual races’ described in common frogs in the 1930s.     

Characterization of sex chromosomes in rainbow trout and coho salmon using fluorescence in situ hybridization (FISH)

With the aim of characterizing the sex chromosomes of rainbow trout (Oncorhynchus mykiss) and to identify the sex chromosomes of coho salmon (O. kisutch), we used molecular markers OmyP9, 5S rDNA, and a growth hormone gene fragment (GH2), as FISH probes. Metaphase chromosomes were obtained from lymphocyte cultures from farm specimens of rainbow trout and coho salmon. Rainbow trout sex marker OmyP9 hybridizes on the sex chromosomes of rainbow trout, while in coho salmon, fluorescent signals were localized in the medial region of the long arm of one subtelocentric chromosome pair. This hybridization pattern together with the hybridization of a GH2 intron probe on a chromosome pair having the same morphology, suggests that a subtelocentric pair could be the sex chromosomes in this species. We confirm that in rainbow trout, one of the two loci for 5S rDNA genes is on the X chromosome. In males of this species that lack a heteromorphic sex pair (XX males), the 5S rDNA probe hybridized to both subtelocentrics This finding is discussed in relation to the hypothesis of intraspecific polymorphism of sex chromosomes in rainbow trout.     

Resolution of sex chromosome constitution by genomic in situ hybridization and fluorescence in situ hybridization with (TTAGG) n telomeric probe in some species of Lepidoptera

We have developed a simple method to resolve the sex chromosome constitution in females of Lepidoptera by using a combination of genomic in situ hybridization (GISH) and fluorescence in situ hybridization with (TTAGG) _n telomeric probe (telomere-FISH). In pachytene configurations of sex chromosomes, GISH differentiated W heterochromatin and telomere-FISH detected the chromosome ends. With this method we showed that Antheraea yamamai has a standard system with a fully differentiated W–Z sex chromosome pair. In Orgyia antiqua, we confirmed the presence of neo-W and neo-Z chromosomes, which most probably originated by fusion of the ancestral W and Z with an autosome pair. In contrast to earlier data, Orgyia thyellina females displayed a neo-ZW₁W₂ sex chromosome constitution. A neo-WZ₁Z₂ trivalent was found in females of Samia cynthia subsp. indet., originating from a population in Nagano, Japan. Whereas another subspecies collected in Sapporo, Japan, and determined as S. cynthia walkeri, showed a neo-W/neo-Z bivalent similar to O. antiqua, and the subspecies S. cynthia ricini showed a Z univalent (a Z/ZZ system). The combination of GISH and telomere-FISH enabled us to acquire not only reliable information about sex chromosome constitution but also an insight into sex chromosome evolution in Lepidoptera.     

Simple repetitive sequences are associated with differentiation of the sex chromosomes in the guppy fish

Summary Hybridization of restriction enzymedigested genomic guppy (Poecilia reticulata, Poeciliidae) DNA with the oligonucleotide probe (GACA)₄ revealed a male-specific simple tandem repeat locus, which defines the Y chromosome in outbred populations. The related (GATA)₄ probe identifies certain males with the red color phenotype. In contrast only in two out of eight laboratory guppy strains was the typical (GACA)₄ band observed. By specific staining of the constitutive heterochromatin one pair of chromosomes could also be identified as the sex chromosomes, confirming the XX/XY mechanism of sex determination. All males exhibit Y chromosomes with a large region of telomeric heterochromatin. Hybridization in situ with nonradioactively labeled oligonucleotide probes localized the (GACA)_n repeats to this heterochromatic portion. Together these results may be regarded as a recent paradigm for the differentiation of heteromorphic sex chromosomes from a pair of autosomes during the course of evolution. According to the fish model system, this may have happened in several independent consecutive steps.     

Contribution to the description of an endemic Turkish Salix species

Abstract

The sex genetic determinants of the dioecious species Asparagus offcinalis are codified on the chromosome pair n. 5 and inherited as a monomendelian trait; since the dominant alleal controls the development of androecium, the males are heterozygous and the female homozygous. The male plants of asparagus are know to be superiour respect to the female ones for important yield components, therefore one objectiv of the breeding is the synthesis of all-male hybrids. That is possible by crossing female plants (m/m) with male plaits (M/M) homozygous for sex pair chromosome. The synthes of such kind of males by selfing the rare andromonoecious plants, involves several problems which can be overcome by using the in vitro anther culture technique. At our Institute this technique has been sistematically applied during the last twenty years and allowed to regenerate doubled haploid clones which were evaluated in the field for a minimum period of four years. The best male and female clones were then utilized as parents of all-male F₁ hybrids. Following omparative varietal trials in different location for several years, the best F₁ all-mal hybrids were identified and released to private seed companies for the production of commercial seed.     

Multiple sex chromosome system of X1X1X2X2/X1X2)Y type in lutjanid fish, Lutjanus quinquelineatus (Perciformes)

The karyotype and other chromosomal markers as revealed by C-banding and Ag-staining were studied in Lutjanus quinquelineatus and L. kasmira (Lutjanidae, Perciformes). While in latter species, the karyotype was invariably composed of 48 acrocentric chromosomes in both sexes, in L. quinquelineatus the female karyotype had exclusively 48 acrocentric chromosomes (2n = 48) but that of the male consisted of one large metacentric and 46 acrocentric chromosomes (2n = 47). The chromosomes in the first meiotic division in males showed 22 bivalents and one trivalent, which was formed by an end-to-end association and a chiasmatic association. Multiple sex chromosome system of X₁X₁X₂X₂/X₁X₂Y type resulting from single Robertsonian fusion between the original Y chromosome and an autosome was hypothesized to produce neo-Y sex chromosome. The multiple sex chromosome system of L. quinquelineatus appears to be at the early stage of the differentiation. The positive C-banded heterochromatin was situated exclusively in centromeric regions of all chromosomes in both species. Similarly, nucleolus organizer region sites were identified in the pericentromeric region of one middle-sized pair of chromosomes in both species. The cellular DNA contents were the same (3.3 pg) between the sexes and among this species and related species.     

Karyotype,heterochromatin content and meiotic features ofPoecilocera picta (Orthoptera,Acrididae)

Cytological study of three distinctly separated populations ofPoecilocera picta revealed a chromosome number of 2N = 18 + XO/ XX. Except for the hemizygosity of a procentric heterochromatic block in the M₆ pair of the Bangalore population, the basic karyotype of the three populations is markedly similar. The autosomal karyotype formula is 2Lt + 4Mt + 1 Mst + 2S st and the telocentric X chromosome is the longest of the complement. All bivalents at pachytene carried procentric heterochromatic blocks. The M₄ is the nucleolus organiser with the NOR region situated interstitially but proximal to the centromere. About 11 μm (4%) of the total (290 μm) autosomal pachytene complement is heterochromatic; a major portion of it is contributed by the S₉ pair which is mostly heterochromatic. Chiasmata are localized proximally and distally and in the S₉ pair their formation is confined to the short procentric euchromatic segment of the long arm. Female meiosis did not reveal any chromomere pattern at pachytene and, unlike in the male, the sex bivalent in the female is indistinguishable from the autosomal bivalents. G- and C-banding patterns in males showed procentric bands in all the chromosomes. In addition there are eight telomeric and two interstitial bands which are C negative. The S₉ pair showed only two bands. The G-banding pattern of the sex chromosome in meiosis showed only a centric band while the heterochromatic body of the facultatively heterochromatic X remained G negative.     

XY<Subscript>1</Subscript>Y<Subscript>2</Subscript> chromosome system in <Emphasis Type="Italic">Salinomys delicatus</Emphasis> (Rodentia,Cricetidae)

Salinomys delicatus is considered a rare species due to its restricted and patchy distribution, poor records and low abundances. It is also the phyllotine with the lowest known diploid chromosome number (2n = 18), however its sex chromosome system has never been described. Here, we studied the chromosomes of six females and three males with bands G, C, DAPI/CMA₃ and meiosis. In males, the chromosome number was 2n = 19, with one large metacentric X-chromosome and two medium-sized acrocentrics absent in females. The karyotype of females was the same as previously described (2n = 18, FN = 32), with X-chromosomes being metacentric and the largest elements of the complement. In males, the two acrocentrics and the large metacentric form a trivalent in meiotic prophase. This indicates that S. delicatus has XY₁Y₂ sex chromosomes, which is confirmed by G and DAPI bands. Constitutive heterochromatin (CH) is restricted to small pericentromeric blocks in all chromosomes. The X-chromosome shows the largest block of centromeric CH, which could favor the establishment of this X-autosome translocation. This sex chromosome system is rare in mammals and, compared with other phyllotine rodents, S. delicatus seems to have undergone a major chromosome restructuring during its karyotypic evolution.     

The influence of the sex chromosome on the number of tailrings in mus musculus

Summary A cross between two strains of mice with different numbers of tailrings which had previously been analyzed as representing mainly a difference in one gene now has been analyzed further with the result that the cross appears to be one between strains differing in at least two genes, one lying in an autosome and the other one in the sex chromosome. Proof for this is the fact that in F₁ there is a difference in the number of tailrings between the reciprocal males, but not between the reciprocal females. The same phenomenon is also reported as observed in another cross of two strains not related to the first pair. The preponderance of males in the recessive group of F₂ is another indication of the influence of the sex chromosome on the number of tailrings.     

Molecular cytogenetic characterization of <Emphasis Type="Italic">Rumex papillaris</Emphasis>, a dioecious plant with an XX/XY<Subscript>1</Subscript>Y<Subscript>2</Subscript> sex chromosome system

Rumex papillaris Boiss, & Reut., an Iberian endemic, belongs to the section Acetosa of the genus Rumex whose main representative is R. acetosa L., a species intensively studied in relation to sex-chromosome evolution. Here, we characterize cytogenetically the chromosomal complement of R. papillaris in an effort to enhance future comparative genomic approaches and to better our understanding of sex chromosome structure in plants. Rumex papillaris, as is common in this group, is a dioecious species characterized by the presence of a multiple sex chromosome system (with females 2n = 12 + XX and males 2n = 12 + XY₁Y₂). Except for the X chromosome both Y chromosomes are the longest in the karyotype and appear heterochromatic due to the accumulation of at least two satellite DNA families, RAE180 and RAYSI. Each chromosome of pair VI has an additional major heterochromatin block at the distal region of the short arm. These supernumerary heterochromatic blocks are occupied by RAE730 satellite DNA family. The Y-related RAE180 family is also present in an additional minor autosomal locus. Our comparative study of the chromosomal organization of the different satellite-DNA sequences in XX/XY and XX/XY₁Y₂ Rumex species demonstrates that of active mechanisms of heterochromatin amplification occurred and were accompanied by chromosomal rearrangements giving rise to the multiple XX/XY₁Y₂ chromosome systems observed in Rumex. Additionally, Y₁ and Y₂ chromosomes have undergone further rearrangements leading to differential patterns of Y-heterochromatin distribution between Rumex species with multiple sex chromosome systems.     

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

The male chromosome complement of Psophus stridulus (L.) (Orthoptera: Acrididae) has been analyzed by using orcein staining, C-banding and silver impregnation. During spermatogenesis only one pair of autosomes (M₉) shows an active nucleolar organizer region located in a C-banded constriction. There are other chromosome pairs with constrictions but these do not show nucleolar activity. The relationship between these constrictions and the C-banding pattern exhibited by this species is analyzed.In a sample of 83 males from five populations, two different supernumerary chromosomes were observed. Four males had a metacentric B-chromosome (B^m) similar in size to the sex chromosome and mitotically stable. Its meiotic behaviour indicates that it is an isochromosome. An additional small B-chromosome (B⁸) was also found in a single follicle of one individual carrying the B^m.A high rate of abnormal spermatids (macrospermatids) was scored in the individuals carrying B's. This proportion is notably higher in the follicle containing both the B^m and the B⁸.     

Whole chromosome painting reveals independent origin of sex chromosomes in closely related forms of a fish species

The wolf fish Hoplias malabaricus includes well differentiated sex systems (XY and X₁X₂Y in karyomorphs B and D, respectively), a nascent XY pair (karyomorph C) and not recognized sex chromosomes (karyomorph A). We performed the evolutionary analysis of these sex chromosomes, using two X chromosome-specific probes derived by microdissection from the XY and X₁X₂Y sex systems. A putative-sex pair in karyomorph A was identified, from which the differentiated XY system was evolved, as well as the clearly evolutionary relationship between the nascent XY system and the origin of the multiple X₁X₂Y chromosomes. The lack of recognizable signals on the sex chromosomes after the reciprocal cross-FISH experiments highlighted that they evolved independently from non-homologous autosomal pairs. It is noteworthy that these distinct pathways occur inside the same nominal species, thus exposing the high plasticity of sex chromosome evolution in lower vertebrates. Possible mechanisms underlying this sex determination liability are also discussed.     

Studies of the species barrier between Drosophila subobscura and D. madeirensis IV. A genetic dissection of the X chromosome for speciation genes

The genetics of four traits contributing to the isolation mechanism between the two closely related species of Drosophila belonging to the obscura group, D. subobscura and D. madeirensis, have been investigated, especially regarding the influence exerted by the X chromosome. This chromosome has been roughly dissected genetically by the use of four markers. It was found that factors affecting viability of backcross males are spread from the centromeric end of the chromosome up the region marked by Bx. Three sections were responsible for male sterility/fertility. The abnormal head shape of the backcross males was affected by factor(s) on the madeirensis and the subobscura sex chromosome located at the region of MAD1 inversion. Finally, an abnormal trait in these males (presence of extra sex combs) was found to be controlled by four sections, two on the madeirensis X chromosome and two on the subobscura one.     

The mechanism of sex determination in Rumex acetosella

Summary Cytogenetic studies were made with particular emphasis on the sex-determining mechanism in Rumex acetosella (6 x = 42) and its hybrids (F ₁, F ₂, BC ₁ and BC ₂) with R. hastatulus (synthetic 4 x = 16 = 4 A +4 X = and 4 x = 18 = 4 A + 2 (X Y ₁ Y ₂) = ). Rumex acetosella was almost strictly dioecious with 5050 male and female. Breeding tests revealed that the males were heterogametic. The longest chromosomes (S), usually two, are the sex chromosomes of this hexaploid species. The S chromosomes are homomorphic in both male and female. The sex chromosome: autosome ratios, and the strong epistatic male effect of the S ^M chromosome in the polyploid dioecious species and in the hybrids, are evidence of an X/Y Melandrium type sex-determining mechanism controlled by a single pair of homomorphic sex chromosomes. Thus, the sex chromosome formula of the males was S ^F S ^M and that of females was S ^F S ^F. The present approach is a new method for resolving the sex-determining mechanism in a dioecious species.     

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

A chromosome study was carried out on a number of European and Central Asiatic diploid green toad populations by means of standard and various other chromosome banding and staining methods (Ag-NOR-, Q-, CMA₃-, late replicating [LR] banding pattern, C- and sequential C-banding + CMA₃ + DAPI). This study revealed the remarkable karyological uniformity of specimens from all populations, with the only exception being specimens from a Moldavian population, where one chromosome pair was heteromorphic. Though similar in shape, size and with an identical heterochromatin distribution, the difference in the heteromorphic pair was due to a large inverted segment on its long arms. This heteromorphism was restricted to females, suggesting a female heterogametic sex chromosome system of ZZ/ZW type at a very early step of differentiation.