Sex chromosomes and origin of males and sex mosaics of the parthenogenetic stick insect Carausius morosus Br.

The chromosome complements of sporadic males and masculinized females of the thelytokous phasmid Carausius morosus Br. could be analysed in spermatogonia and ovarian follicle cells. Masculinized females with ovaries, ovotestes or testes have the female chromosome number, i.e., 61 autosomes and three sex chromosomes. The sex chromosomes, one being longer than the other two, are metacentric. In one masculinized female with testes the three sex chromosomes were different, apparently through a reciprocal translocation. The masculinized females are considered to be intersexes (phenotypic sex determination). The chromosome complement of males differs from that of females by lacking either one of the sex chromosomes or only a segment of one of these chromosomes (genotypic sex determination). The deleted sex chromosomes appear as acrocentrics and may have arisen through a chiasma between a translocated segment in one sex chromosome and its untransposed homologous region in another sex chromosome. One apparently telocentric sex chromosome may have originated from centric fission together with loss of the other arm. The sex chromosomes are positively heteropycntoic in the psermatogonia, also in those of masculinized females. En bloc heterochromatinization of the sex chromosomes, which seems to be under the direct or indirect control of one or more sites on the sex chromosomes themselves, functions in sex determination. The sex determination does not give a decisive answer to the question whether di-, tri-, or tetraploidy is involved.     

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.     

Cytogenetic characterization and description of an XX/XY1Y2 sex chromosome system in catfish Harttia carvalhoi (Siluriformes, Loricariidae)

Karyotypic and cytogenetic characteristics of catfish Harttia carvalhoi (Paraíba do Sul River basin, S?o Paulo State, Brazil) were investigated using differential staining techniques (C-banding, Ag-staining) and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. The diploid chromosome number of females was 2n = 52 and their karyotype was composed of nine pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric and four pairs of acrocentric chromosomes. The diploid chromosome number of males was invariably 2n = 53 and their karyotype consisted of one large unpaired metacentric, eight pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric, four pairs of acrocentric plus two middle-sized acrocentric chromosomes. The differences between female and male karyotypes indicated the presence of a sex chromosome system of XX/XY1Y2 type, where the X is the largest metacentric and Y1 and Y2 are the two additional middle-sized acrocentric chromosomes of the male karyotype. The major rDNA sites as revealed by FISH with an 18S rDNA probe were located in the pericentromeric region of the largest pair of acrocentric chromosomes. FISH with a 5S rDNA probe revealed two sites: an interstitial site located in the largest pair of acrocentric chromosomes, and a pericentromeric site in a smaller metacentric pair of chromosomes. Translocations or centric fusions in the ancestral 2n = 54 karyotype is hypothesized for the origin of such multiple sex chromosome systems where females are fixed translocation homozygotes whereas males are fixed translocation heterozygotes. The available cytogenetic data for representatives of the genus Harttia examined so far indicate large kayotype diversity.     

Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes)

Chromosomes of a species of Eigenmannia presenting a X₁X₁X₂X₂:X₁X₂Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A₃ (CMA₃) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA₃/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G+C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought. Received: 1 April 1999; in revised form: 16 October 1999 / Accepted: 4 December 1999     

Evidence for two successive pericentric inversions in sex lampbrush chromosomes of Rana rugosa (Anura: Ranidae)

The objective of this study was to clarify the course of inversions by which a ZW sex chromosome dimorphism has become established in Rana rugosa. Fortunately, R. rugosa preserves three different forms of sex chromosomes in the several isolated populations. In both males and females, the homomorphic sex chromosomes from Hiroshima were closely similar to Z, while those from Isehara were slightly different from the Z. Females from Hirosaki demonstrated heteromorphic sex chromosomes. In this study, the configuration and pairing behavior of sex lampbrush chromosomes were examined in the female offspring produced from a cross between a female from Hiroshima and a male from Isehara, as well as the female offspring of a female from Hirosaki and the male from Isehara. For the sex lampbrush chromosomes from Hiroshima and Isehara, chiasmata were exclusively formed between the distal regions of the long arms of one sex chromosome and the terminal regions of the short arms of the other. As a result, landmarks arranged in reverse order were observed in the achiasmatic regions of these chromosomes. For the sex lampbrush chromosomes from Isehara and Hirosaki, on the other hand, chiasma formation was mainly confined to the lower half of the chromosomes corresponding to the long arms, and the landmarks in the achiasmatic regions of these chromosomes were disposed in the opposite direction to each other. These results seem to indicate that in the primitive sex chromosomes of the Hiroshima type two pericentric inversions occurred, leading to the differentiation of the W chromosomes. This is the first report to substantiate the process of sex chromosome differentiation experimentally. Received: 10 November 1996; in revised form: 22 April 1997 / Accepted: 24 April 1997     

Unequal X Chromosomes in Bradysia Hygida (Diptera:Sciaridae) Females: Karyotype Assembly and Morphometric Analysis

The mitotic chromosomes of Bradysia hygida(Diptera:Sciaridae) neuroblast cells are described together with their morphometric data. Giemsa-stained neuroblast chromosomes from female and male larvae confirm the chromosome number of this species, 2n=8 (XX) and 2n=7 (XO), respectively. The karyotype assembly reveals two metacentric autosomic pairs, the A and B chromosome; a subtelocentric, the C chromosome, the smallest one; and a sexual unequal metacentric pair, X chromosome, in female karyotype and a one sexual metacentric X chromosome in male. The implications of the unequal X chromosome pair are discussed.     

The origin of the genetical diversity of Microtus mandarinus chromosomes

Here we describe our comparative studies on two types of X chromosomes, namely X(M) and X(SM,) of the mandarin vole (Microtus mandarinus). By chromosome G- and C-banding analysis, we have found that two different types of X chromosomes exist in mandarin voles. The two types of X chromosomes present two different G- and C-banding patterns: the X(M) chromosome is a longer metacentric X chromosome which is C-band negative; and the X(SM) is a shorter submetacentric X chromosome which has one C-band at the centromere and another one at the middle part of the short arm. The X(SM) has 6 G-bands including one on the kinetochore, one in the middle of the short arm, and four on the long arm. The X(M) has 7 G-bands including one on the kinetochore, two on the short arm, and four on the long arm. We have further found that female voles can be grouped into three types based on the composition of the X chromosome but the male voles have only one type. The three female groups are: (1) female voles (X(M)X(SM)), in which the two X chromosomes are different, the longer one is metacentric and the shorter is submetacentric; (2) female vole (X(SM)X(SM)), in which the two X chromosomes are both submetacentric; (3) female vole (X(M)O), in which there is only one X chromosome that is metacentric. Surprisingly, we have never found female voles with X(M)X(M), females with X(SM)O or males with X(M)Y. We hypothesize that the X(SM) chromosome is derived from the X(M) through its breakage and re-joining. The paper also discusses the formation of X(M)O females.     

On the sex chromosome trivalent in some Lepidoptera females

In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The broken chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY₁Y₂ for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.Dedicated to Doctor Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Karyotyping of female and male Hediste japonica (Polychaeta, Annelida) in comparison with those of two closely related species, H. diadroma and H. atoka

Karyotypes of females and males of the brackish-water polychaete Hediste japonica sensu stricto, collected from the Ariake Sea, Japan, were examined by using regenerating tails. We used the Giemsa staining method and a computer-assisted image-analyzing system for the identification of each chromosome pair. The somatic chromosome number was 2n=28. The presence of an XX-XY (male heterogametic) sex chromosome system was determined from well-spread metaphase plates of somatic cells. The type of sex chromosomes related with phenotype exactly. The metacentric Y chromosome was much larger than the submetacentric X chromosome. All autosomes were metacentric. The karyotype of this species was compared with those of the other two closely related species (H. diadroma and H. atoka). The karyotypes of all the three species were similar to one another.     

Diversification of a ZZ/ZW sex chromosome system in Characidium fish (Crenuchidae, Characiformes)

Karyotype and other chromosomal markers of Characidium cf. gomesi were analyzed using conventional (Giemsa-staining, Ag-NOR and C-banding) and molecular (Fluorescent in situ hybridization (FISH) with 18S and 5S rDNA biotinylated probes) techniques. Both sexes had invariably diploid chromosome number 2n = 50 while karyotypes of males and females differed. That of male consisted of 32 metacentric + 18 submetacentric chromosomes and that of female consisted 31 metacentric + 18 submetacentric + 1 subtelocentric chromosomes. The Z chromosome was medium-sized metacentric, while W was highly heterochromatinized subtelocentric element. NORs as revealed by Ag-staining were situated at 2–7 telomeric regions while FISH with 18S probes showed consistently 10 signals at telomeric regions. FISH with 5S rDNA probe showed constantly signals at one metacentric pair. Distribution of centromeric heterochromatin was mostly in all chromosome pairs, besides some telomeric sites. The common origin of the sex chromosome system of ZZ/ZW type in the karyotypes of other representatives of the genus analyzed so far might be hypothesized based on biogeography and partial phylogeny of the group.     

The first cytogenetic characterization of atemnids: pseudoscorpions with the highest chromosome numbers (arachnida: pseudoscorpiones)

The karyotypes of pseudoscorpions of the family Atemnidae (Arachnida: Pseudoscorpiones) were studied for the first time. Karyotype data for 7 species have been obtained. The diploid chromosome numbers of most species considerably exceed the numbers reported in pseudoscorpions so far, with males ranging between 65 and 143. In spite of this, the sex chromosome system of atemnids is characterized by the same features that are found in the majority of other pseudoscorpions with an X0 system; the X chromosome is metacentric and is the largest chromosome or one of the largest chromosomes of the karyotype. Male meiotic cells of Atemnus politus contain 1 or 2 autosome multivalents; most specimens had 2 multivalents. The multivalents were composed of 4, 6, 8 or 10 chromosomes. Multivalent number and structure was consistent within each of the studied individuals. The same number of chromosomes in all of the males examined suggests that multivalents are generated by reciprocal translocations. The high diversity of multivalents suggests considerable range of translocation heterozygosity in the studied population.     

Chromosome evolution in the erythrinid fish, Erythrinus erythrinus (Teleostei: Characiformes)

The genus Erythrinus belongs to the family Erythrinidae, a neotropical fish group. This genus contains only two described species, Erythrinus erythrinus being the most widely distributed in South America. Six samples of this species from five distinct Brazilian localities and one from Argentina were studied cytogenetically. Four groups were identified on the basis of their chromosomal features. Group A comprises three samples, all with 2n = 54 chromosomes, a very similar karyotypic structure, and the absence of chromosome differentiation between males and females. One sample bears up to four supernumerary microchromosomes, which look like 'double minute chromosomes' in appearance. Groups B-D comprise the three remaining samples, all sharing an X(1)X(1)X(2)X(2)/X(1)X(2)Y sex chromosome system. Group B shows 2n = 54/53 chromosomes in females and males, respectively, and also shows up to three supernumerary microchromosomes. Groups C and D show 2n=52/51 chromosomes in females and males, respectively, but differ in the number of metacentric, subtelocentric, and acrocentric chromosomes. In these three groups (B-D), the Y is a metacentric chromosome clearly identified as the largest in the complement. The present results offer clear evidence that local samples of E. erythrinus retain exclusive and fixed chromosomal features, indicating that this species may represent a species complex.     

A novel Robertsonian translocation in a family of Walker hounds.

A 5-year-old female Walker hound was presented to the Washington State University Veterinary Teaching Hospital as a result of a narrowing of the vulva, which prevented natural breeding. All other physical and clinical findings were normal. Cytogenetic analysis disclosed a chromosome number of 77, with three metacentric chromosomes comprised of two X chromosomes and a Robertsonian translocation of two acrocentric autosomes, chromosomes 21 and 33. Cytogenetic analysis of two full-sister siblings with histories of absence of estrus disclosed one with the same translocation and one with a normal female chromosome constitution. The propositus was artificially inseminated with semen from a karyotypically normal male Walker hound and gave birth to nine live grossly normal pups, six females and three males. Another female pup was stillborn but was grossly normal. Cytogenetic analysis of the live pups disclosed that four (three males and one female) of the nine had the same translocation in all lymphocytes. The remaining five pups (five females) had normal female chromosome constitutions. The litter size was average for this breed. This is a previously unreported Robertsonian translocation in dogs.     

Sex chromosomes in the sockeye salmon: a Y-autosome fusion

Chromosomes of 21 sockeye salmon [Oncorhynchus nerka (Walbaum)] from three locations in Washington state were examined. All males had 57 chromosomes, while all females had 58 chromosomes. Both sexes had 104 chromosome arms. It appears that in males of this species the Y chromosome and an autosome have fused to form a metacentric chromosome.     

Cytological studies of certain desert mammals of Saudi Arabia 5. The karyotype of Meriones rex

Male and female specimens of Meriones rex were collected from agricultural areas of Asir province in Saudi Arabia. The mitotic and meiotic chromosomes were analysed and the diploid number of chromosomes was found to be 38. The karyotype showed 24 metacentric, 10 submetacentric and 2 acrocentric autosomes. The sex chromosomes were represented by a medium-sized metacentric X and a small metacentric Y chromosome. The fundamental number (FN) was 74.This project has been supported by Research Center of College of Science, King Saud University (Zoo/1402/11), Riyadh, Saudi Arabia.     

Ultrastructure,meiotic behavior,and evolution of sex chromosomes of the genus Ellobius

The whole-mount SC preparations from males of three species of the genus Ellobius (Ellobius fuscocapillus, Ellobius lutescens), and Ellobius tancrei were studied by electron microscopy. In the males of Ellobius fuscocapillus, behavioral peculiarities of the sex bivalent (viz. the normal male heterozygosity) are characterized by early complete desynapsis of sex chromosomes (X, Y), occurring at late pachytene-early diplotene. The karyotype of species Ellobius lutescens is unique for mammals. In both sexes it is characterized by an odd number of chromosomes (2n=17). At prophase I the unpaired chromosome 9 is not involved in synapsis with other chromosomes and forms a sex body at the end of pachytene.The complete Robertsonian fan has been described for superspecies Ellobius tancrei. As shown on the basis of G-band patterns the male and female sex chromosomes are cytologically indistinguishable.Analysis of whole-mount SC preparations revealed the formation of a closed sex SC bivalent and showed some morphological differences in the axes of sex chromosomes at meiotic prophase I. A number of assumptions are made about the relationship between the behavior of sex chromosomes, their evolution and the sex determination system in the studied species of genus Ellobius.

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Karyological and gonadal sex of eels(Anguilla anguilla) from the German Bight and the lower River Elbe

Yellow eels(Anguilla anguilla) taken during summer from random commercial trapnet samples in the littoral area of Helgoland (n=116) and from a freshwater area of the River Elbe near Hamburg (n=109) were examined with regard to their karyological (i.e. existence of female sex chromosomes) and gonadal sex. In 47 % and 21 % of the two samples, respectively, chromosomes were unidentifiable because of insufficient numbers of mitotic plates. All eels from Helgoland, except one phenotypically undetermined fish, exhibited female gonads: 48 had female sex chromosomes and 13 were karyologically males. As found previously in the River Elbe, eels with male gonads predominated (n=55); 25 were undifferentiated. Of the gonadal males 26 were karyological males and 16 karyological females; the rest could not be identified by chromosome patterns. In contrast, all but one of the Elbe eels with female gonads (n=28) had female sex chromosomes. Some aspects of the sex reversal documented in the eel are considered.     

Occurrence of macro B chromosomes in Astyanax scabripinnis paranae (Pisces,Characiformes, Characidae)

B chromosomes occur in several Neotropical fish species. Cytogenetic analysis of 27 specimens (15 females and 12 males) of Astyanax scabripinnis paranae from the Araquá river (a small headwater tributary of the Tietê river) shows that this population has 2n=50 chromosomes (4M+30 SM+4ST+12A), two chromosome pairs with NORs and conspicuous C-band positive blocks in the terminal position of the long arm of four chromosome pairs. In this population, eight females presented 2n=51 chromosomes and the extra chromosome was a large metacentric similar in size and morphology to the first chromosome pair in the karotype. This accessory chromosome is entirely heterochromatic in C-banded metaphases and shows a late replication pattern evidenced by BrdU incorporation. There was no significant correlation between the presence of B chromosomes and increased NOR activity at the P>0.05 level. Some aspects related to these B chromosomes are discussed.     

黄鳝体内寄生胃瘤线虫的染色体核型及G-带分析

采用常规空气干燥法制片,对寄生于黄鳝(Monopterus albus)体腔内的胃瘤线虫(Eustrongylidesignotus)染色体核型进行分析。结果表明:胃瘤线虫体细胞有12条染色体,为二倍体,核型公式为2n=12=10 m+2 sm。由5对常染色体和1对性染色体组成,性别决定模式为XX-XY,其中X、Y和1～4号染色体都为中着丝粒染色体,5号为亚中着丝粒染色体。每对染色体都有特定的G-带带型。