Karyotype, Ag-NOR, CMA3 and SEM studies in a fish (Mystus tengara, Bagridae) with indication of female heterogamety

Somatic karyotypes in M. tengara contained 54 chromosomes, comprising 26 homomorphic pairs in both sexes and one pair of heteromorphic nature in female (one big submetacentric and one small subtelocentric chromosomes), while in males this pair was homomorphic (with two big sub-metacentric chromosomes). The Nucleolus Organizer Regions (NORs) were located at one arm of the suspected sex elements in both sexes, while another pair of metacentric chromosomes (No.7) also showed Ag-positive arm. The CMA3 technique revealed relatively bright fluorescing zones in the regions of chromosomes that showed Ag-positive staining, revealing thereby the preponderance of GC-rich active sites of rRNA genes in NORs. SEM studies revealed clear heteromorphism to exist in the elements suspected as sex chromosomes in females.     

Chromosomes of lemuriformes. II. Chromosome polymorphism in Lemur fulvus collaris (E. Geoffroy 1812).

Two previously unreported diploid numbers, 2N = 50 and 2N = 51, from five individual Lemur fulvus collaris are described. In both chromosome complements, the nombre fondamental is 64. The 2N = 50 complement is composed of 7 pairs of bi-armed chromosomes, 17 pairs of acrocentric chromosomes with small short arms, and acrocentric sex chromosomes. The 2N = 51 complement is identical with these exceptions: Only one member equivalent to bi-armed pair 6 of L.f. collaris (2N = 50) is present, and two extra acrocentrics are found in the 2N = 51 complement. G-banding analyses suggest that these chromosomes are a heteromorphic pair of the Robertsonian type. This conculsion is supported by evidence from studies of meiotic pairing relationships of the three chromosomes and the complements of hybrids resulting from interspecific matings. Comparison of the 2N = 50 and 2N = 51 complements with a published 2N = 48 complement suggests that these new karyotypes do not provide a lineal link between the 2N = 52 and 2N = 48 karyotypes (Rumpler, Y., and R. Albignac 1969 C.R. Soc. Biol., 163: 1989-1992).     

黑斑蛙的减数分裂研究

本文研究了黑斑蛙的减数分裂,发现其性染色体所形成的性二价体主要呈末端与末端联接,浓缩期占79.6％,中期Ⅰ占75％,这进一步证明黑斑蛙确实存在XY型性别决定机制,这种XY型性染色体虽形态相同,但已发生了质的分化,可能是同型异质。黑斑蛙的性染色体并不形成性泡,少数二价体有中间交叉。     

Mammalian sex chromosomes: design or accident?

Mammalian sex chromosomes evolved (and are still evolving) from a homomorphic pair by the progressive loss of active genes from the Y chromosome. Among the changes that have accompanied this differentiation, it is difficult to determine causes, effects and correlates. Comparative studies suggest that the choice of a gene, and thus a chromosome pair, to control the sex-determining pathway may be quite arbitrary, and that sex chromosomes and sex-determining genes are more likely to be the products of random changes than the products of selection for function.     

The karyotype of the golden monkey (Rhinopithecus r. roxellanae)

In this paper, the karyotype and G-banding pattern of the chromosomes of cultured peripheral blood lymphocytes in R. r. roxellanae were investigated. The chromosome number of this species is 44 in both sexes. In R. r. roxellanae, as in other monkeys, sex is determined by specific sex chromosomes, i.e. the male is XY and the female is XX. The 21 pairs of autosomes consist of 7 pairs of metacentric chromoomes, 13 pairs of submetacentric chromosomes and one acrocentric pair. Chromosome measurements were made from highly enlarged photographic prints. They included the relative length, arm ratio and centromere index of each chromosome. Both chromosomal and chromatid aberrations were observed. They were 0·67 and 2%, respectively. Finally, G-banding pattern analysis of chromosomes of R. r. roxellanae were carried out. The results show that each homologous pair has its own special banding pattern, so that each of them is easily recognizable. Idiograms of chromosome complements with the Giemsa banding pattern are constructed.     

Karyotypic characterization of Iheringichthys labrosus (Pisces, Pimelodidae): C-, G- and restriction endonuclease banding

Various chromosomal banding techniques were utilized on the catfish, Iheringichthys labrosus, taken from the Capivara Reservoir. C-banding regions were evidenced in telomeric regions of most of the chromosomes. The B microchromosome appeared totally heterochromatic. The restriction endonuclease AluI produced a banding pattern similar to C-banding in some chromosomes; the B microchromosome, when present, was not digested by this enzyme and remained stained. G-banding was conspicuous in almost all the chromosomes, with the centromeres showing negative G-banding. When the restriction endonuclease BamHI was used, most of the telomeres remained intact, while some centromeres were weakly digested. The B chromosome was also not digested by this enzyme. The first pair of chromosomes showed a pattern of longitudinal bands, both with G-banding and BamHI; this was more evident with G-banding. This banding pattern can be considered a chromosomal marker for this population of I. labrosus.     

达乌尔黄鼠显带染色体的研究

达乌尔黄鼠分布在我国北方及蒙古和苏联等区域,对牧草及农田危害甚大。有关达乌尔黄鼠的核型国内外已有报道(Lyapunova等,1970;蔡有余等,1985;马继霞等,1985)。签于其染色体的一些特征,达乌尔黄鼠有可能成为染色体工程及检测环境诱变剂等方面的实验材料。虽然苏联Lyapunova等(1978,1980)对黄鼠属某些种的G-带和C-带进行过比较研究,我国蔡有余等(1985)对达乌尔黄鼠的C-带和Ag-NOR进行了观察,但无法对其染色体进行逐个地准确识别,特别是对Χ染体色的正确识别。为此,我们对达乌尔黄鼠的显带染色体进行了较详细的研究。     

大熊猫(Ailuropoda melanolenca)显带染色体的研究

大熊猫系我国特产的世界珍稀动物,素有“活化石”和“国宝”之称。限于材料来源,虽有核型的少数报道（邓承宗等,1980;陈文元等,1984;Newnham et al.,1966）,但研究尚不够深入。1980年,Wurster-Hill和Bush首先报道了大熊猫（）的显带核型,并与杂交熊等比较,探讨了大熊猫的分类地位。本文对四只大熊猫的G带、C带核型和Ag-NORs作了分析,绘制了G带核型模式图,并提出了某些商榷的意见。     

Metaphase karyotypes and G-banding in sandflies of the Lutzomyia longipalpis complex

Mitotic metaphase chromosomes (2n = 8) from brain cells of fourth instar sandfly larvae of four geographical strains of the Lutzomyia longipaplis complex were examined microscopically, with bright-field illumination, after staining by a new G-banding technique involving exposure of air-dried chromosome preparations to quinacrine and ultraviolet light. Differences of G-banding and/or position of the centromere on chromosome 4 (the smallest chromosome pair) distinguished four putative sibling species from Costa Rica, Colombia and Brazil (distinctive populations from Jacobina and Lapinha Caves). The karyotype of the population from Jacobina, Brazil, showed an apparently plesiomorphic pattern of G-banding. On the basis of their recognizably different mitotic karyotypes, cytogenetic identification of separate taxa in the L. longipalpis complex should be useful for specific female vector competence and ecology studies.     

赤斑羚和斑羚核型比较研究

本文对赤斑羚（ＮａｅｍｏｒｈｅｄｕｓＣｒａｎｂｒｏｏｋｉ）和斑羚（Ｎ．ｇｏｒａｌｇｒｉｓｅｕｓ）的染色体Ｇ带、Ｃ带和Ａｇ－ＮＯＲｓ的数目、分布等作了较详细的比较研究。赤斑羚２ｎ＝５６全部为近端着丝粒染色体,Ｎ．Ｆ＝５４;斑羚２ｎ＝５４,除Ｎｏ．３是亚中着丝粒染色体外,具有丰富的异染色质;二者Ｇ带带纹相似程度高,其Ｎｏ．３长臂Ｇ带带纹相似。斑羚的Ｎｏ．３短臂与赤斑羚Ｎｏ．２７近端着丝粒染色体的大小、     

Karyotype of Brazilian Anopheles albitarsis sensu lato (Diptera:Culicidae)

Anopheles (Nyssorhynchus) albitarsis sensu lato is an important malaria vector in Brazil, especially in the Brazilian Amazon region. Chromosome preparations of fourth-instar larvae of A. albitarsis from Iranduba and Coari (AM) and Ilha Comprida (SP) were analyzed for karyotype determination and to improve cytogenetic identification of this species. Anopheles albitarsis possesses 2n = 6 chromosomes, with two pairs (submetacentric and metacentric) of autosomes and one pair of sex chromosomes, with X-Y dimorphism. The sex pair is homomorphic and acrocentric in females and heteromorphic in males, with a punctiform Y chromosome. Somatic pairing was detected in the prometaphase and metaphase chromosomes of the three A. albitarsis populations. Apparently, sex chromosome evolution in the Culicidae does not function as does evolution in the Culicidae, since it occurs in the subfamily Anophelinae, which possesses heteromorphic sex chromosomes and is regarded as primitive, based on several criteria. These karyotype data on the albitarsis complex reinforce the hypothesis that sex chromosome evolution in the subfamily Anophelinae is conserved, and the variation revealed in the mean size of chromosomes in three populations indicates that selective pressure in these populations is occurring only at a genetic level.     

Why plant chromosomes do not show G-bands

Summary Giemsa techniques have refused to reveal G-banding patterns in plant chromosomes. Whatever has been differentially stained so far in plant chromosomes by various techniques represents constitutive heterochromatin (redefined in this paper). Patterns of this type must not be confused with the G-banding patterns of higher vertebrates which reveal an additional chromosome segmentation beyond that due to constitutive heterochromatin. The absence of G-bands in plants is explained as follows: 1) Plant chromosomes in metaphase contain much more DNA than G-banding vertebrate chromosomes of comparable length. At such a high degree of contraction vertebrate chromosomes too would not show G-bands, simply for optical reasons. 2) The striking correspondence of pachytene chromomeres and mitotic G-bands in higher vertebrates suggests that pachytene chromomeres are G-band equivalents, and that this may also be the case in plants. G-banded vertebrate chromosomes are on the average only 2.3 times shorter in mitosis than in pachytene; the chromomeric pattern therefore still can be shown. In contrast, plant chromosomes are approximately 10 times shorter at mitotic metaphase; their pachytene-like arrangement of chromomeres is therefore no longer demonstrable.     

Cytogenetic analysis of some Brazilian marsupials (Didelphidae: Marsupialia)

Three species of marsupials from the Amazon region (Marmosa cinerea, Caluromys lanatus, and Didelphis marsupialis) and two from the region of S?o Paulo (Didelphis marsupialis and Didelphis albiventris) were studied. The G-banding pattern of the species with 2n = 14 (M. cinerea and C. lanatus) was very similar, as well as the pattern of G-bands in the species with 22 chromosomes (Didelphis). All of the autosomes of M. cinerea and D. albiventris have centromeric C-bands and the Y chromosome is totally C-band positive. The long arm of the M. cinerea X chromosome is completely C-band positive except for a negative band close to the centromeric region. In D. albiventris the long arm of the X chromosome is C-band positive except for a negative band close to the telomeric region. In M. cinerea the silver-stained nucleolar organizer regions (Ag-NORs) are found in the acrocentric chromosomes, being located in the telomeric region of one pair and in the centromeric region of the other pair. Caluromys lanatus has centromeric Ag-NORs in one acrocentric and in one submetacentric chromosome pairs. Didelphis marsupialis has three chromosome pairs with telomeric Ag-NORs. In D. albiventris the Ag-NORs are terminal and located in both arms of one pair and in the long arm of two pairs of chromosomes.     

A new look at the evolution of avian sex chromosomes

Birds have a ubiquitous, female heterogametic, ZW sex chromosome system. The current model suggests that the Z chromosome and its degraded partner, the W chromosome, evolved from an ancestral pair of autosomes independently from the mammalian XY male heteromorphic sex chromosomes--which are similar in size, but not gene content (Graves, 1995; Fridolfsson et al., 1998). Furthermore the degradation of the W has been proposed to be progressive, with the basal clade of birds (the ratites) possessing virtually homomorphic sex chromosomes and the more recently derived birds (the carinates) possessing highly heteromorphic sex chromosomes (Ohno, 1967; Solari, 1993). Recent findings have suggested an alternative to independent evolution of bird and mammal chromosomes, in which an XY system took over directly from an ancestral ZW system. Here we examine recent research into avian sex chromosomes and offer alternative suggestions as to their evolution.     

大麦G—显带核型的研究

本文报道了 ASG 法处理的三个栽培大麦(Hordeum Vulgare)品种 G-带的核型研究。结果表明无论是早中期或中期染色体都显示出了密切邻近的、多重的 G-带带纹。在有丝分裂过程中染色体愈浓缩带纹数目愈少。同源染色体之间带纹分布的位置、染色深浅以及带纹数目都基本一致,可以较为准确地进行配对。同一分裂时期不同染色体的 G-带带纹各具一定的特点,可以作为鉴别的标记。讨论了显带技术和中期染色体的 G-带等问题。     

Studies on G-Banding Karyotype in Barley (Hordeum vulgare)

G-banding karyotypes of three cultivars in barley were analyzed. Multiple closely adjacent G-bands were able to be observed in each early metaphase or metaphase chromosome treatted by an ASG method. The more concentrated the chromosome, the less was the number of G-bands during mitosis. The position of band distribution, staining degree and band numbers between homologous chromosomes were basically identical. Chromosome pairing for karyotype analysis could be carried out more accurately. G-banding patterns of different chromosome pairs were not the same, they could be used as the markers to distinguish one from another chromosome pair. During the same mitotic stage the banding patterns including number, relative position and staining degree of the bands between different cultivars were basically the same, but they had differences in the size and staining degree of some bands near centromeres. G-banding technique and G-banding of metaphase chromosomes were discussed.     

Frequency of chromosome polymorphism in Rattus rattus collected in Japan

This paper deals with a population survey of chromosome polymorphism of Rattus rattus collected in Japan and the results of their test crosses. All the animals had diploid 42 chromosomes, but three chromosome pairs, Nos. 1, 9 and 13, were polymorphic in respect to acro- and subtelocentric chromosomes. Frequency of No. 1 chromosome polymorphism in 453 rats collected in 19 localities showed 343 rats (75.5%) with acrocentric homomorphic pair (A/A), 90 (19.9%) with aerocentric and subtelocentric heteromorphic pair (A/S) and the remaining 20 (4.4%) with subtelocentric homomorphic pair (S/S). All animals collected in northern and northwestern Japan showed only the A/A pair, while those collected in southern and southeastern Japan showed A/A, A/S and S/S polymorphism. The latter group was also classified into 3 populations (east, southeast and south) by the different frequency of the subtelocentric chromosome. Progeny tests revealed that segregation of A/A, A/S and S/S types from F₁ hybrids between various chromosome combinations was not significantly different from the theoretical one. However, the number of animals with A/S pair was always slightly higher than the other two types, while those with S/S pair slightly fewer. Local differences of the chromosome polymorphism in Japan were considered due to the result of migration and selection of the rats with S/S chromosome type.Contribution No. 817 from the National Institute of Genetics, Japan. Supported in part by a grant-in-aid from the Ministry of Education of Japan (Scientific Expedition in 1968, and No. 8801 in 1969).     

Origin and evolution of mammalian sex chromosomes

Mammals present an XX/XY system of chromosomal sex determination, males being the heterogametic sex. Comparative studies of the gene content of sex chromosomes from the major groups of mammals reveal that most Y genes have X-linked homologues and that X and Y share homologous pseudoautosomal regions. These observations, together with the presence of the two homologous regions (pseudoautosomal regions) at the tips of the sex chromosomes, suggest that these chromosomes began as an ordinary pair of homologous autosomes. Birds present a ZW/ZZ system of chromosomal sex determination where females are the heterogametic sex. In this case, avian sex chromosomes are derived from different pairs of autosomes than mammals. The evolutionary pathway from the autosomal homomorphic departure to the present-day heteromorphic sex chromosomes in mammals includes suppression of X-Y recombination, differentiation of the nascent non-recombining regions, and progressive autosomal addition and attrition of the sex chromosomes. Recent results indicate that the event marking the beginning of the differentiation between the extant X and Y chromosomes occurred about 300 million years ago.