Karyological criteria of 15 African species of Sesbania, including five new records, are presented. A diploid number of 2n =12 (x=6) has been found in 12 species, 2n =14 (x=7) in onespecies and a tetraploid number of 2n =4x=24 was recorded in S. formosa and S. grandiflora. The karyotype in the examined species is symmetric. However, considerable variation exists in chromo-some size among the species studied. The result of the present study confirm that x=6 may be considered the basic number in the genus. Our observations further indicate that Sesbania is a primitive genus in its tribe Robinieae from which other genera may have evolved through aneuploid and polyploid changes.
Analysis of karyotype including somatic chromosome number determination, total chromosome length and volume, estimation of 4C DNA content and Interphase Nuclear Volume (INV) were carried out in 6 species of Melocactus of the family Cactaceae. Somatic chromosome number recorded 2n=22 in Melocactus bahiensis, M curvispinus, M robustispinus, M. townsendii and 2n=44 in M longispinus, M. matanzanus for the first time. Significant interspecific variation in nuclear DNA amount was recorded. The 4C DNA content varied from 20.55 pg in M. townsendii to 40.80 pg in M. longispinus. The correlation coefficient studies showed that the genomic chromosome length, chromosome volume and INV were possitively correlated. No interdependent was found between 4C DNA content and chromosome length or volume and INV. The structural alterations in the chromosomes as well as loss or addition of highly repetitive sequences in the genome showed variations in nuclear DNA at interspecific level indicating a macro- and micro-evolution of the species.
Chromosomal analysis of the three Egyptian species, Unio elongatulus (Family : Unionidae), Mutela rostrata (Family : Mutlelidae) and Corbicula fluminalis (Family : Corbiculidae) have been studied. The diploid chromosome number of these three species are 2n=28, 2n=20 and 2n=26 respectively. Comparative analysis of the karyotypic data of these three species had been discussed. To the best of the author knowledge, these results are reported for the first time in Egypt.
Cytomorphological and phytochemical studies in a chimeric mutant obtained through colchicine treatment in mulberry were conducted. Uniform distribution of ploidal chimera (2n+4n) was detected in different vegetative parts. Meiosis in the chimeric plant was highly irregular. Persistence of chimera in vegetative clonal generations was observed. Distinct morphological changes along with an increase in phenol and a decrease in sugar content were observed in the mutant. Significance of ploidal chimera in the improvement of mulberry is discussed.
Three samples of Sinipta dalmani polymorphic for the M4 pericentric inversion were assayed for chromosomal variation and allozymic variation at 18 loci (9 enzymatic systems). No sig-nificant differences in inversion frequencies between two samples of the same population were found (early and late spring). This was considered compatible with the absence of directional selection on adult viability for the M4 inversion. Gene flow between two populations was statistically significant when calculated either from chromosomal or from enzymatic data. A tendency to association between the Ldh-11 allele and the standard sequence was observed.
Cytogenetical studies with regard to meiotic behavior of chromosomes was carried out on seven cultivars of Upland cotton Gossypium hirsutum and their hybrids. In total 24 genotypes were analysed. The genotypes studied showed genomic differences with regard to chiasma formation, alternate and adjacent quadrivalents and hexavalent formation. Cluster analysis of cytological data grouped those genotypes having 1106 genome in their background in one cluster. Those with B-557 and Bakhtegan background formed the second cluster. Cultivars Siokra and Tashkandl formed separate clusters indicating their genomic differences from the other genotypes studied. Factor analysis showed that different means of chiasma reduction and multivalent formation are the most variable meiotic characters among the genotypes studied.
The meiotic behaviour of a spontaneous paracentric inversion was analyzed in a male of Dichroplus pratensis from a population of the Sierra de la Ventana hybrid zone (Argentina), characterized by four Robertsonian polymorphisms. The mutant was 2n=15, homozygous for the 3/4 tanslocation and heterozygous for translocations 1/2 and 5/6. The inversion was located in arm 2 of the 1-1.2-2 trivalent and comprised the first half of its distal end, involving about 25% of the chro-mosome length. Analysis of pairing at three pachytene substages showed that the main mode of synapsis was homologous, with a high frequency of complete loop formation at early pachytene. No synaptic adjustment seems to occur, and homosynapsis is significantly correlated with crossing over within the inverted region. As a result, high frequencies of bridge and fragment configurations occur at first anaphase/telophase stages which produce significant levels of unreduced cells at second meiotic division and later, macrospermatids. Microspermatids are also abundant because of micronuclei formation by lagging acentric fragments. These results suggest a deletereous effect of paracentric inversions in D. pratensis due to production of aberrant recombinant chromosomes and formation of increased levels of abnormal sperm. Furthermore, since the paracentric inversion induces a chiasma repatterning in the involved chromosome arm, a strong relationship between homologous pairing and crossing over is evident. This is discussed in the light of current models of chromosome synapsis.
Anaesthetists have reported complaints of headache, nausea, fatigue, dizziness, as well as heart and liver diseases as a consequence of chronic exposure to low ambient levels of anaesthetic gases in the operation theater. Reports of foetal wastage, bad obstetric history and infertility have also been recorded. This study was amined at evaluating the damage to chromosomes by quantifying the damage in terms of the number of chromosomal aberrations (CAs) seen when compared to equally matched controls. The study showed that the anaesthetists showed a significantly higher number of chromosomal aberrations than did the controls. This is evidence of genotoxicity, and suggestions are made to reduce the exposure in the theater by the installation of efficient scavenging systems and leak proof ventilation systems on a top priority basis.
The subfamily Stethaprioninae, a monophyletic group among characids, is almost unknown from the cytogenetic viewpoint. This paper shows the first chromosome characterization of Poptella paraguayensis, an endemic species of the Paraguay river basin. Analysis in Giemsa-stained preparations showed 2n=50 : 10 M+26SM+8ST+6A. The nucleolar organizing regions (NORs) detected by silver nitrate and GC-specific fluorochrome mithramycin (MM) staining showed two NOR-bearing chromosomes in the diploid complement. DA/DAPI staining showed no differential fluorescence along the chromosomes. C-banding evidenced small blocks of heterochromatin in the centromeric and telomeric regions. Phylogenetic relationships between the Stethaprioninae and other characids are discussed on the base of chromosome data.
In this paper we present the cytogenetic data of Rhynchospora cephalotes (L.) Vahl, in the section Cephalotae Kükenth. Chromosome numbers of R. cephalotes are assumed as 2n=17, 18 and 19. According to our data, it may be proposed that the disploids have evolved from processes of fusion and fission of the chromosomes of euploids.
Karyotype analysis and behaviour of B-chromosomes at meiosis in Centaurea kandavanensis are reported. The number of B-chromosomes was 0 to 3 in both somatic and gametic cells. The somatic karyotype consisted of eight metacentric pairs, two submetacentric pairs and 0-3B-submetacentric chromosomes. Analysis of chromosome behaviour at meiosis showed that the increase of number of B-chromosomes increased the mean chiasma frequency of A-chromosomes in pollen mother cells.
The karyotypes of 50 plants of Paris tetraphylla were analyzed by observing the Cbanded segment patterns of chromosomes in Miike (Mi), Kunimi (Kn) and Kikuchi (Kk) populations in Kumamoto Prefecture of Kyushu. Various karyotypes were observed in each population, i.e., 49 different karyotypes in Mi, 50 in Kn and 38 in Kk. The karyotypes tended to be heterozygous for most of the homologous chromosome pairs. This indicated that the karyotypic structure of the populations may be maintained mainly by random crossing. Nevertheless, the frequencies of karyotypes homozygous for all chromosome pairs were higher than the expected values, which were calculated using random combinations of homo- and heterozygous pairs in respective populations. Moreover, in most of the chromosomes composing the genome, the observed frequencies of homozygous pairs were significantly higher than the expected ones, which were calculated randomly based on the observed frequencies of different chromosome types in each population. The inbreeding coefficients (f) indicated that a low degree of inbreeding occurred in the natural conditions. The pollination tests indicated that the species was both self- and crosscompatible and fertilized by predominant cross-and inferior self-pollination. This was supported by the collection of air-born pollen grains in the population. In the conclusion, the populations of P. tetraphylla were maintained predominantly by random breeding with a low degree of simultaneous inbreeding.
A developmental mutant of A. nidulans strain (MC430) was obtained by NTG treatment. The mutant shows secondary conidiophores, multiple tiers of sterigmata, absence of conidiophore pigmentation and foot-cell alterations. This phenotype was determined by a gene (medA430) mapped on the chromosome I. The map distance between the medA430 and galD loci was 23.7 cM.It's the same location of the medA locus. The foot-cell abnormalities present in this mutant strain indicate that it is a carrier of a new allele of the medA gene. It's very useful for future analysis with regard to the Med protein action on the conidiophore development.
The karyotypic study of 33 specimens of geographic isolated populations of Trichomycterus paolence (Eigenmann 1918) collected from three brook streams revealed a modal diploid number of 54 and three different chromosomal formula : 44 metacentrics (M) +8 submetacentrics (SM) +2 subtelocentrics (ST), 40 metacentrics (M) +14 submetacentrics (SM), and 46 metacentrics (M) +6 submetacentrics (SM) +2 subtelocentrics (ST). The nucleolar organizer regions (NORs) were interstitially located on the long arms of the same largest submetacentric chromosome pair in the karyotypes in two of three samples analyzed; in the third sample, the NORs were also interstitially located on the long arm as well, but in the largest metacentric pair of chromosomes. C-banding analysis showed centromeric and pericentromeric patterns of DNA heterochromatinization only in a few chromosome pairs in all three populations analysed. Differences in chromosome and karyotype organization among the individuals can constitute interesting markers for specific populations and play its role in the process of diversification within this group.