Preliminary Observatiun of the Sex-Chromosomes of Rumex acetosa in China

The Rumex acetosa L. in China possesses sex-chromosomes 2n=12A+XX in female plant and 2n=12A+XY1Y2 in male plant. The sex-chromosomes of male plant exhibit a chain of trivalent (Y1-X-Y2) in diakinesis of PMC meiosis. At metaphase Ⅰ, they make a V-shaped or a ring configuration. Some of them may form a XY-bivalent and a Y-univalent. Finally two kinds of reale gametes e.g. 6A+X and .6A+YY, are produced. Monoecious plant may be found in R. acetosa and has 22 chromosomes (22=18A+ XX+YY). This is a triplont with sterility. Cells with different chromosome number in the same plant have also seen in R. acetosa, and such plant never blooms in its life.     

陕西野生啤酒花染色体形态的研究

作者观察了陕西野生啤酒花的染色体数目和形态,分析了这种野生啤酒花及栽培啤酒花的核型,为植物分类及啤酒花育种工作提供了资料。     

Heterochromosomes in Mytilicola intestinalis Steuer (Copepoda)

The male and female diploid complements in Mytilicola are formed both by 22 chromosomes. Two different somatic metaphase figures are found: with two minute-size chromosomes and with three minute-size chromosomes. The study of meiosis has shown that the female sex is heterogametic. The chromosome complement is 10_II+XX in the male and 10_II+XY in the female. A bivalent formed by two different-length homologues, is to be seen in the female meiosis at pachytene; it shows, sometimes, a light positive hetero-pycnosis.     

Heterochromatin diversity and cyclic responses to selective silver staining in Aedes aegypti (L.)

In interphase cells of Aedes aegypti (L.) (2n=4+ XX/XY), only the nucleolus responded to selective silver staining. The secondary constriction on chromosome 3 remained unresponsive at all times but the six centromeres were identified throughout mitosis from early prophase as well as those stages of meiosis subsequent to diplotene. The centromeric blocks were not synonymous with the pericentric heterochromatin revealed by C-banding. X chromosomes without an intercalary C-band were newly discovered in Ae. aegypti in the Bangalore strain. Sequential Q-or Hoechst 33258/C-banding in this and the Trinidad-30 strain revealed intercalary heterochromatin diversity within and between strains and also differences between intercalary and pericentric heterochromatin.     

Nucleolus organizing regions and semi-persistent nucleolus during meiosis in Spartocera fusca (Thunberg) (Coreidae, Heteroptera)

The Coreidae are cytogenetically characterized by possessing holokinetic chromosomes and a pre-reductional type of meiosis. The modal diploid chromosome number of the family is 21, with a pair of m chromosomes and an XO/XX sex chromosome determining system. Spartocera fusca presents 2n=23/24=20+2m+XO/20+2m+XX (male/female). Meiosis follows the general pattern described for heteropterans, with a diffuse stage after pachytene and a particular chromosome arrangement at both metaphase plates. S. fusca presents some cytogenetic peculiarities: the X chromosome shows a secondary constriction in a medial position, which is not a nucleolus organizing region. It has been revealed by in situ hybridization with a rDNA probe that the NOR is localized at the telomeric region of one autosomal pair. Furthermore, during the meiosis of three specimens of S. fusca a semi-persistent nucleolus was detected from early meiotic prophase until telophase II; the presence of this semi-persistent nucleolus together with the long diffuse stage detected in the specimens suggest that a continuous biosynthetic activity is required for spermiogenesis. These observations could be related to differences in the environmental, and therefore, physiological conditions of the analyzed individuals.     

Karyotype,sex determination and male meiosis in three benthic water bugs (Hemiptera: Nepomorpha: Aphelocheiridae)

We report here the first chromosome numbers for benthic water bugs (Nepomorpha: Aphelocheiridae). All three studied species, Aphelocheirus aestivalis (Fabricius, 1794), A. murcius Nieser and Millán, 1989 and Aphelocheirus sp. from Ebro River (northern Spain), have karyotype 2n = 22 + XX/X(0) and inverted sequence of the X chromosome divisions in male meiosis. The similarity and difference in cytogenetic traits between Aphelocheiridae and other families of Nepomorpha are shortly discussed.     

Aberrant chromosomal sex-determining mechanisms in mammals, with special reference to species with XY females

Both mouse and man have the common XX/XY sex chromosome mechanism. The X chromosome is of original size (5-6% of female haploid set) and the Y is one of the smallest chromosomes of the complement. But there are species, belonging to a variety of orders, with composite sex chromosomes and multiple sex chromosome systems: XX/XY1Y2 and X1X1X2X2/X1X2Y. The original X or the Y, respectively, have been translocated on to an autosome. The sex chromosomes of these species segregate regularly at meiosis; two kinds of sperm and one kind of egg are produced and the sex ratio is the normal 1:1. Individuals with deviating sex chromosome constitutions (XXY, XYY, XO or XXX) have been found in at least 16 mammalian species other than man. The phenotypic manifestations of these deviating constitutions are briefly discussed. In the dog, pig, goat and mouse exceptional XX males and in the horse XY females attract attention. Certain rodents have complicated mechanisms for sex determination: Ellobius lutescens and Tokudaia osimensis have XO males and females. Both sexes of Microtus oregoni are gonosomic mosaics (male OY/XY, female XX/XO). The wood lemming, Myopus schisticolor, the collared lemming, Dirostonyx torquatus, and perhaps also one or two species of the genus Akodon have XX and XY females and XY males. The XX, X*X and X*Y females of Myopus and Dicrostonyx are discussed in some detail. The wood lemming has proved to be a favourable natural model for studies in sex determination, because a large variety of sex chromosome aneuploids are born relatively frequently. The dosage model for sex determination is not supported by the wood lemming data. For male development, genes on both the X and the Y chromosomes are necessary.     

Numerical and structural variations of the X chromosomes and no. 2 autosomes in mandarin vole, Microtus mandarinus (Rodentia)

Here we describe our studies on Microtus mandarinus faeceus of Jiangyan in Jiangsu province of China. By karyotype and G-banding analysis we have found variation in chromosome number and polymorphisms of the X chromosome and the second pair of autosomes of the subspecies. Chromosome number of the subspecies is 2n=47-50. The subspecies has three kinds of chromosomal sex: XX, XO and XY, among which one of the X chromosomes is subtelocentric (X(ST)) and the other is metacentric (X(M)). After comparing karyotypes of different subspecies, we found the specific cytogenetic characteristics of Microtus mandarinus, that is they have three kinds of chromosomal sex: XX, XO and XY; X chromosomes are heteromorphic; the chromosome number of female individuals are one less than male individuals; chromosome number of XX individuals are equal to that of XO ones. We hypothesize that Robertsonian translocation is the main reason of the polymorphism of the second pair of autosomes and variety of chromosome number, and it also causes the chromosome number evolution in different subspecies of Microtus mandarinus.     

山地原花蝽核型研究(半翅目,花蝽科)

采用姬姆萨染色压片法,对花蝽科山地原花蝽性细胞进行了核型研究.结果表明该种单倍染色体组成为n=14A+XY,为无交叉减数分裂,性染色体经历后减数分裂,上述核型特征为阐明臭虫型内不同科的系统发育关系具有重要意义.     

Chromosomal diversity and evolution in the ground beetle genus Bembidion and related taxa (Coleoptera: Carabidae: Trechitae)

Chromosome numbers and sex chromosome systems of 154 previously unstudied Bembidion species are described. The genus is nearly uniform: males of 176 of 205 species are 2n=22+XY. Karyotypes are presented for 30 species. There is some variation among species in size of Y and size of autosomes. Within most species autosomes are subequal in size, and metacentric or submetacentric. Subterminal secondary constrictions and B chromosomes are reported from several species.The supertribe Trechitae (Zolini + Trechini + Pogonini + Bembidiini) is hypothesized to be primitively male 2n=22+X or 24+X, and the ancestral Bembidion stock 2n=22+XY. Conclusions are based on the most parsimonious hypothesis of ancestral state given an inferred phylogeny of the group, rather than the widespread-is-primitive arguments used previously. Evolution within Bembidion away from the presumably-primitive 2n=22+XY is discussed. Six lineages have lost Y chromosomes; seven have undergone changes in autosome number. It is not known why such changes are so scarce, nor what particular rearrangements led to the observed diversity. Nonetheless, the cytogenetic data can be used to infer a monophyletic origin of groups possessing derived chromosome numbers or sex chromosomes, and to help resolve species limits.     

Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan

The grasshopper Podisma sapporensis consists of two main chromosome races in Hokkaido. The western group of populations of P. sapporensis, belonging to the XO race, has a diploid number of chromosomes 2n = 23 in the male and 2n = 24 in the female (sex determination XO male/XX female). The eastern group of populations of this species, belonging to the XY race, differs from the western one as a result of Robertsonian translocation between the originally acrocentric X chromosome and M5 autosome in homozygous state, having resulted in the forming of chromosome sex determination neo-XY male/neo-XX female (2n = 22). These races are geographically isolated by the mountainous system consisting of the Mts Daisetsu and Hidaka range, occupying the central part of the island. The hybrid zones between the races have not so far been discovered. Various levels of polymorphism for the pericentric inversions and C-banding variation exist in different chromosomes throughout populations in both chromosome races. In some solitary populations (the population at the summit of Mt Yotei, populations in the vicinity of Naganuma, Oketo, and Tanno) pericentric inversions are fixed in some pairs of chromosomes, which enables marking of the discrete karyomorphes. In the Mt Daisengen population all chromosomes are two-armed as a result of fixing the pericentric inversions. These facts contradict karyotypical conservatism of the tribe Podismini. The level of diversity of P. sapporensis karyotypes could provide a new perspective on the evolutionary process of different karyotype in Orthoptera. The considerable occurrence of polymorphism in chromosomes suggests that karyotypic diversification is undergoing in P. sapporensis. The authors also proposed that P. sapporensis would be divided into four chromosome subraces in the XO chromosome race and two chromosome subraces in the XY race, on the basis of karyotypic features. These races may have been established by fundamental climatic changes during the glacial epoch.     

Chromosome numbers in antlions (Myrmeleontidae) and owlflies (Ascalaphidae) (Insecta,Neuroptera)

A short review of main cytogenetic features of insects belonging to the sister neuropteran families Myrmeleontidae (antlions) and Ascalaphidae (owlflies) is presented, with a particular focus on their chromosome numbers and sex chromosome systems. Diploid male chromosome numbers are listed for 37 species, 21 genera from 9 subfamilies of the antlions as well as for seven species and five genera of the owlfly subfamily Ascalaphinae. The list includes data on five species whose karyotypes were studied in the present work. It is shown here that antlions and owlflies share a simple sex chromosome system XY/XX; a similar range of chromosome numbers, 2n = 14-26 and 2n = 18-22 respectively; and a peculiar distant pairing of sex chromosomes in male meiosis. Usually the karyotype is particularly stable within a genus but there are some exceptions in both families (in the genera Palpares and Libelloides respectively). The Myrmeleontidae and Ascalaphidae differ in their modal chromosome numbers. Most antlions exhibit 2n = 14 and 16, and Palparinae are the only subfamily characterized by higher numbers, 2n = 22, 24, and 26. The higher numbers, 2n = 20 and 22, are also found in owlflies. Since the Palparinae represent a basal phylogenetic lineage of the Myrmeleontidae, it is hypothesized that higher chromosome numbers are ancestral for antlions and were inherited from the common ancestor of Myrmeleontidae + Ascalaphidae. They were preserved in the Palparinae (Myrmeleontidae), but changed via chromosomal fusions toward lower numbers in other subfamilies.     

Cytotaxonomy of the triatominae (Reduviidae: Hemiptera)

The chromosome number and meiotic cycle of 20 species of Triatominae have been investigated. In the male, there are five types of chromosome complement: 20+XY, 20+X₁X₂Y, 20+X₁X₂X₃Y, 18+XY and 22+XY.The cytological data suggest that the type number for the subfamily is 22 (20+XY). In the hybrids: Triatoma barberi () and T. protracta (), anomalous behavior of certain chromosomes has been observed. Phylogenetic relationships based on chromosome evidence in the subfamily have been discussed. It is suggested that fragmentation is the major factor for chromosome evolution in the group.     

Freemartinism in red deer (Cervus elaphus L.)

Several mixed-sex twins were produced by red deer treated with progesterone and pregnant mare's serum gonadotrophin. Of seven females karyotyped, two were 68,XX/68,XY chimeras. One male had the same chimeric karyotype as its female co-twin. These are the first reported cases of freemartinism in deer.     

Testicular Development Induced by a Recessive Mutation during Gonadal Differentiation of Female Common Carp (Cyprinus carpio, L.)

The phenotypic effects of a new recessive mutation mas ⁻¹, which in homozygous condition induces testicular development in XX animals of common carp ( Cyprinus carpio L.), are described. Sexual differentiation of XX; mas ⁻⁺/ mas ⁻¹ and XX; mas ⁻¹/ mas ⁻¹ animals was compared with the gonad development of XX wild type females and XY males. In XX females gonadal differentiation starts with the formation of an ovarian cavity and entry into meiosis of germ cells at around 80 days post hatching (ph). Male gonads remain quiescent until 120 days ph during which period they develop a network of loose connective tissue. Spermatogenesis starts with tubule formation and the differentiation of germ cells into spermatogonia type B. Heterozygous XX; mas ⁻⁺/ mas ⁻¹ animals developed as normal females, but in homozygous XX; mas ⁻¹/ mas ⁻¹ animals two types of gonad development were observed. In the first type, germ cells did not enter meiosis until 100 days ph when they differentiated as spermatogonia. An ovarian cavity was not formed but male specific connective tissue developed instead. These gonad developed as normal testes. In the second type, germ cells differentiated at 80 days ph as either oocytes or spermatocytes, which resulted in the gonads developing as ovotestes. The formation of an ovarian cavity was in most cases incomplete. The phenotypic effects of mas ⁻¹ are interpreted as a timing mismatch between mas activation and female sex differentiation.     

Sex chromosome differences among the three races (alpha, beta, gamma) of the snail intermediate host of Schistosoma mekongi, Neotricula aperta

Chromosome analyses were performed on three races (alpha, beta, gamma) of Neotricula aperta which were previously reported to show variation in the chromosome number and pairing in meiosis. We used an air-drying method, which was more reliable for chromosome preparations from fresh animal tissues than a squash method. Each of the races had the same number of chromosomes, 2n=33 for males, and 2n=34 for females. The sex determination system was XO type (male: 32+X, female: 32+XX). The sex chromosome of each race was distinct in its morphology, but not in its length. Karyotyping revealed that the X-chromosome of the alpha race was metacentric (M), whereas it was acrocentric (A) in the beta and the gamma races. An association between the X-chromosome and a small autosome in meiosis suggested that a neo-Y chromosome probably lies in the terminal region of the small autosome.     

Chromosome banding in Amphibia. XXII. Atypical y chromosomes in Gastrotheca walkeri and Gastrotheca ovifera (Anura,Hylidae)

The chromosomes of the rare South American marsupial frogs Gastrotheca walkeri and G. ovifera were extensively reexamined with various banding techniques. The karyotypes of both species are distinguished by a new category of XY female symbol /XX male symbol female sex chromosomes. The unusual Y chromosomes are characterized by containing the least amount of constitutive heterochromatin in the karyotypes. This is in contrast to all previously known amphibian Y chromosomes and does not fit the evolutionary model of early XY differentiation in vertebrates. In male meiosis, the heteromorphic XY chromosomes of both species still exhibit the same pairing configurations as the autosomes. DNA flow cytometric measurements show the nuclear DNA amount of G. walkeri to be 10.90 pg. The significance of the XY/XX sex chromosomes of these marsupial frogs, the various classes of constitutive heterochromatin detected, and the data obtained from meiotic analyses are discussed in detail.     

Die Cytogenetik der Flöhe (Aphaniptera)

The phylogenetical relationship of the fleas (Aphaniptera=Siphonaptera) to the other orders of the Insecta remains unsolved. Comparative studies of the cytology of the fleas are undertaken in an attempt to elucidate this problem. Two populations of Xenopsylla cheopis Rothschild, 1903, exhibit a chromosome complement of 2n = 14 A + X₁X₂Y (male): 14 A+X₁X₁X₂X₂ (female). The X₁X₂Y-sex-trivalent is restricted to the male meiosis, in oogenesis two sex-bivalents (X₁X₁ and X₂X₂) are formed. One population of Leptopsylla segnis Schönherr, 1811 shows 2n =18 A + XY (male): 18 A+XX (female). The high chromosome number of X. cheopis, L. segnis, and N. fasciatus (Bayreuther, 1969), the diffuse premeiotic stage in the spermatogenesis of the threespecies investigated and the multiple sex-chromosome-mechanisms of X. cheopis and N. fasciatus do not support the concept of a closer phylogenetic relationship between the Aphaniptera and Nematocera, but do not preclude the possibility of a kinship of Aphaniptera and Neomecoptera. Additional studies of the cytogenetics of these two orders are required before lasting conclusions can be drawn. The analysis of the chromosome cytology of the fleas of the Marsupialia, which are considered to be the most primitive of all living forms, could prove particularly instructive.     

Sex reversal of genetic females (XX) induced by the transplantation of XY somatic cells in the medaka,Oryzias latipes

In order to investigate the function of gonadal somatic cells in the sex differentiation of germ cells, we produced chimera fish containing both male (XY) and female (XX) cells by means of cell transplantation between blastula embryos in the medaka, Oryzias latipes. Sexually mature chimera fish were obtained from all combinations of recipient and donor genotypes. Most chimeras developed according to the genetic sex of the recipients, whose cells are thought to be dominant in the gonads of chimeras. However, among XX/XY (recipient/donor) chimeras, we obtained three males that differentiated into the donor's sex. Genotyping of their progeny and of strain-specific DNA fragments in their testes showed that, although two of them produced progeny from only XX spermatogenic cells, their testes all contained XY cells. That is, in the two XX/XY chimeras, germ cells consisted of XX cells but testicular somatic cells contained both XX and XY cells, suggesting that the XY somatic cells induced sex reversal of the XX germ cells and the XX somatic cells. The histological examination of developing gonads of XX/XY chimera fry showed that XY donor cells affect the early sex differentiation of germ cells. These results suggest that XY somatic cells start to differentiate into male cells depending on their sex chromosome composition, and that, in the environment produced by XY somatic cells in the medaka, germ cells differentiate into male cells regardless of their sex chromosome composition.     

The number of x chromosomes causes sex differences in adiposity in mice

Sexual dimorphism in body weight, fat distribution, and metabolic disease has been attributed largely to differential effects of male and female gonadal hormones. Here, we report that the number of X chromosomes within cells also contributes to these sex differences. We employed a unique mouse model, known as the "four core genotypes," to distinguish between effects of gonadal sex (testes or ovaries) and sex chromosomes (XX or XY). With this model, we produced gonadal male and female mice carrying XX or XY sex chromosome complements. Mice were gonadectomized to remove the acute effects of gonadal hormones and to uncover effects of sex chromosome complement on obesity. Mice with XX sex chromosomes (relative to XY), regardless of their type of gonad, had up to 2-fold increased adiposity and greater food intake during daylight hours, when mice are normally inactive. Mice with two X chromosomes also had accelerated weight gain on a high fat diet and developed fatty liver and elevated lipid and insulin levels. Further genetic studies with mice carrying XO and XXY chromosome complements revealed that the differences between XX and XY mice are attributable to dosage of the X chromosome, rather than effects of the Y chromosome. A subset of genes that escape X chromosome inactivation exhibited higher expression levels in adipose tissue and liver of XX compared to XY mice, and may contribute to the sex differences in obesity. Overall, our study is the first to identify sex chromosome complement, a factor distinguishing all male and female cells, as a cause of sex differences in obesity and metabolism.