Meiotic analyses at pachytene, anaphase I, telophase I, prophase II, metaphase II and the tetrad stage were carried out on several Capsicum annuum L. plants. The bivalents showed regular chromosome pairing and a nonrandom chiasmata distribution. The mean number of chiasmata per cell were 21.62. Aberrations such as reverse inversion loops in pachytene, dicentric bridghes and fragments in pollen mother cells at anaphase I, telophase I, prophase II, metaphase II and 4, 5, 6 and 7 microspores at the tetrad stage, indicated that these plants were heterozygous for a paracentric inversion, which may involve 1 or more homologous chromosomes. The 84.04% fertility showed that a simple or double crossing-over took place within reverse inversion loops between inverted and normal chromosome segments at pachytene, which reduced fertility by the formation of genetically abnormal gametes.
The Random Amplified Polymorphic DNA (RAPD) technique was used to study DNA profiling of 5 multivoltine silkworm genotypes. The silkworm Bombyx mori. L, (Lepidoptera; Bombycidae) were analyzed using 30 random primers among which 18 polymorphic primers gave 73 amplified products and of which 38.3% were polymorphic. The dendrogram generated using an unweighted pair grouped method with arithmetic averages revealed the pattern of relatedness of 5 genotypes. Genetic similarity co-efficient and cluster analysis were performed by a hierarchical clustering technique. The genetic distances between the clusters and within the clusters estimated 6% variability between the 4 races and Nistari. The results of our study indicate that RAPDs are very efficient in the estimation of genetic diversity in populations that are closely related and acclimatized to local environmental conditions. The polymorphic data obtained from the study can be further utilized for MV genome mapping research and finally to assign function to sequences through biometrical tools. Modern breeding tools like molecular markers which show easily detectable differences among different races of a species offer a wide range of applications for silkworm breeding programs. India is being a country with diverse environmental conditions, the local races are rich reservoirs of many resistant genes, and molecular markers are inevitable tools to study inheritance of such complex genes.
In a study on soybean using gamma rays, we came across with some sterile mutants. Cytological studies of these mutants clearly revealed desynapsis in them. In these sterile plants only few bivalents and a high frequency of univalents have been recorded and they displayed a very high percentage of pollen sterility. Later meiotic stages were also found to be highly disturbed. The plants were identified as male sterile ones as few pods were formed. It might be possible that gamma rays have acted on some genes responsible for synapsis and chiasma formation and resulted in early chiasmate dissociation suggesting that gamma rays can act as a potential tool in the development of male sterile lines. Study of desynaptic mutants is a potentially important source of information on the chiasma maintenance mechanism. These mutants furthermore can provide useful cytological and genetical informations on the male sterility occured in higher plants.
Cytogenetic mechanism of Wolbachia-induced cytoplasmic incompatibility is investigated in the uzifly, Exorista sorbillans, a parasitoid of silkworm, Bombyx mori. The results re-vealed the condensation of chromatin to form the paternal pronucleus upon the sperm entering in to the egg, and subsequently condensed paternal and maternal pronuclei fused to form the diploid zygote in compatible crosses. In fertilized eggs from incompatible crosses, only the maternal pronucleus had individual chromosomes. The uncondensed paternal pronucleus scattered near maternal pronucleus, and in some eggs reappear as a diffused tangled chromatin mass and tend to get fragmented during the first mitotic division. Moreover, the abnormalities in the first mitotic division extend with the fragmentation and nonorientation of chromosomes on equatorial plane of first metaphase plate. The initiation of chromosome separation in late metaphase was an indication of beginning of anaphase in compatible crosses. In case of incompatible crosses, the chromosome separation had not occurred even at late metaphase/early anaphase leading the failure of development of viable embryo. However, abnormal behavior of paternal chromatin does not interfere with mitotic division of maternal chromosomes. The mechanism is discussed with applied strategy for the management of uzifly, Exorista sorbillans.
Low polymorphism in Stylosanthes emphasizes use of inter-specific crosses for the development of mapping population for genetic linkage map. Using 78 F2 individuals of the cross of S. scabra cv. Seca and S. fruticosa, 7 linkage groups were obtained when 81 polymorphic RAPD (Random Amplified Polymorphic DNA) markers were processed. Of these, 53 segregated in expected ratio of 3 : 1 for dominant marker in the F2 generation, 11 markers in 1 : 1 while 17 deviated from the expected ratio. Thirty markers remain unlinked. Total genome length covered by markers in the present partial map is 630.4 cM (centi Morgan) with an average interval of 39.4 cM. The skeleton map developed is being used to place reasonable numbers of RAPD and STS (Sequence Tagged Sites) markers and to identify QTLs (Quantitative Trait Loci) for anthracnose disease, one of the most important disease of the genus Stylosanthes.
Three morphological forms based on the leaf character of Lasia spinosa (L.) Thwaites viz. i) sagittate, ii) lamina dissected and iii) a mixed of sagittate and lamina dissected were cytogenetically investigated. The sagittate form had 2n=27. A minute subtelocentric chromosome was found in the sagittate form. Both lamina dissected and mixed form possessed 2n=26 chromosomes. The centromeric formula of sagittate form was 19m+7sm+1st. It was 9m+15sm+2st in the lamina dissected form and 14m+11sm+1t in the mixed form. The total length of 2n chromosome complement was 102.23 μm in the sagittate form, 57.78 μm in the lamina dissected form and 74.46 μm in the mixed form. In orcein-staining, one satellite was found in sagittate form, 2 in the lamina dissected form and 5 in the mixed form. In CMA-staining, 2 big CMA-positive satellites were found in the sagittate form. Two small CMA-positive satellites were found in the lamina dissected form. The mixed form had 1 big and 1 small satellite. Two CMA-positive bands were found in sagittate, 5 in lamina dissected and 3 in mixed form. The percentage of GC-rich region was 2.88 in the sagittate, 11.23 in the lamina dissected and 6.79 in the mixed form. The above features indicated that the mixed form might be a natural hybrid between the sagittate and the lamina dissected form. Each form possessed specific karyotype which could be applied to elucidate the taxonomic rank of these 3 forms in Lasia spinosa.
Meiotic studies were carried out in 2 different accessions of Tribulus rajasthanensis (Zygophyllaceae), a threatened species of Rajasthan, India. This plant is being over exploited for its multipurpose utility as a fodder and medicinal uses, threatening its occurrence in natural habitat. Two accessions belonging to T. rajasthanensis collected from 5 different locations were cytologically analyzed, which showed the same gametic number of n=12 consistently meiotic analysis in pollen mother cells revealed predominance of ring type over rod bivalents, which had mostly terminalized chiasma, giving terminalization coefficient of 0.93 in both the accessions. Anaphase I distribution of chromosome was normal, although univalents in the form of laggards were often encountered. A significant reduction in percentage pollen stainability could be correlated to rather chromosome associations indicating heterozygosity in the constituent genome T. rajasthanensis. The role of structural/numerical chromosome change in divergence of T. ragasthanensis is discussed in detail.
Detailed karyotype analysis of somatic chromosomes in 5 species of Typhonium Schott. of the family Araceae was carried out for the first time. The chromosome number varied from 2n=16 in T. flagelliforme to 2n=52 in T. diversifollium. Chromosome number 2n=18 and 2n=26 in T. trilobatum and T. roxburghii respectively suggest formation of anueploids during speciation. The asymmetric karyotype revealed structural alterations with 2 distinct types of chromosomes (long and very short types) as evident in different species of Typhonium. Significant variations in chromosome size were observed among the studied species. TF% revealed sub-metacentric long chromosomes in T. flagelliforme (TF value, 33%) and metacentric short chromosomes in T. diversifolium (TF value, 41%). Average chromosome length varied from 2.03 μm in T. diversifolium, a high altitude species (5000–7000 ft), to 8.68 μm in T. flagelliforme, a low land species (70–250 ft). Significant variations were observed in Interphase Nuclear Volume (INV) which varied from 142.05 μm3 in T. trilobatum to 335.02 μm3 in T. flagelliforme; nuclear DNA content varied significantly from 0.199 pg in T. diversifolium to 0.833 pg in T. flagelliforme.
The ultrastructural features of the developing megasporocyte, especially the timing of degeneration of sexual cells during megosporogenesis, and differentiation of aposporous initial cell (AIC) in facultative apomictic guinea grass (Panicum maximum) has been studied. The first degeneration was observed in dyad stage. Accompanying the degeneration of sexual cell, the cell adjacent to the dyad in chalazal side, derived from nucellus began to increase its size of cell and change its organelles and shape, and thus, the cell become to the first AIC usually located in micropylar side. The AIC appeared in order continently adjacent to the first AIC in the chalazal side. However, all of the AICs could become to the mature embryo sac with 4-nucleates. The interdependent patterns of the nucellar cell and AIC, and their relationship are also discussed at subcellular level.
The cytogenetic studies performed in Bixa orellana have reported 2n=14 or 2n=16 chromosomes with little karyotypic information. In this context, an improved cytogenetic protocol using enzymatic maceration of meristematic cellular walls and digital image analysis was applied to B. orellana and B. arborea. In B. arborea, the high-resolution technique, Ag-NOR and C banding methods, and FISH using a probe of 45S rDNA genes, were also performed. Prometaphasic and standard C-metaphasic chromosomes presented well-defined primary and secondary constrictions facilitated the pairing of homologues and assembly of the karyogram for the 2 species. These species showed similar karyotypes with 2n=14 chromosomes, being composed of 5 metacentric pairs (1, 2, 3, 4 and 6) and 2 submetacentric pairs (5 and 7). The chromosome 1 is approximately 2 times as long as the others and possesses the secondary constriction adjacent to the centromere, which suggests that Robertsonian translocation between 2 smaller chromosomes may have occurred during the karyotype evolution of Bixa. Additionally, the active NOR, the NOR-adjacent heterochromatic region and 18S, 5.8S and 26S rDNA genes were identified in the secondary constriction of chromosome 1.
Mouse H-1 (ES) cells (H-1 cells) were examined for polyploidization by demecolcine and K-252a. H-1 cells were highly polyploidized by both demecolcine and K-252a, and died 3 d after their addition, suggesting that polyploidized H-1 cells are sensitive to these drugs. The polyploidized H-1 cells showed alkaline phosphatase activity, suggesting that the pluripotent potential of H-1 cells was maintained through out polyploidization. Although the polyploidized H-1 cells became tentatively diploid or tetraploid after the drug removal, the tetraploid H-1 cells reverted to diploid cells within a month.
Present study attempts to explore the possibility of successfully transferring the jassid resistant genes from 2 wild cotton species G. armourianum (Kearney. (2n=2x=26) D2A) and G. raimondii (Ulbrich. (2n=2x=26) D5) into the cultivated G. hirsutum genotypes through backcrossing and colchiploidy. The investigation revealed that viable seeds of the crosses between G. hirsutum and wild diploid species G. armourianum and G. raimondii were obtained using G. hirsutum as female. The backcrosses using the triploid (F1), as female and tetraploid hirsutum as males was not successful, the reciprocal yielded few seeds. Of 432 F1 plants treated with colchicine, only 2 plants each in the crosses viz., Surabhi×G. raimondii and MCU 9×G. armourianum were polyploidised. The colchiploids C1 (Surabhi×G. raimondii) showed larger leaves, flowers, petal size, petal spot, thick leaves, anther density and increased pollen fertility, whereas C1 (MCU 9×G. armourianum) showed stunted growth, hard stem and thick leaves. Leaf hairiness, leaf texture and leaf shape of the BC1 plants [C1 (Surabhi×G. raimondii)×Surabhi] resembled its donor parent. This indicates that the hairiness, which is an important character conferring jassid resistance, has descended from the wild parent G. raimondii. The BC1 plants of C1 (MCU 9×G. armourianum) had leathery leaves and deterring citronella like odour contributing to jassid resistance is derived from the wild species G. armourianum. The result of cytological investigations also supported the crossability behaviour as a close homology between chromosomes of G. armourianum, G. raimondii and G. hirsutum. In the present study, greater homology observed between A and D genomes aids in production of desirable recombinants despite minor cytological disturbances, as there are successful boll setting and viable seed production. Hence, these species with D genome can be used successfully in gene transfer if fertilization barriers are overcome by novel techniques.
Healthy mice were orally fed with different doses of 3 types of pesticides namely, Metacid (organophosphate insecticide), Profenofos (organophosphate insecticide) and Nimbecidine (biopesticide). The doses were continuously given for consecutive 15 days. Control mice were fed with water. All the doses were given at the rate of 1 ml/100 g body weight. The genotoxic effects in pesticide-treated mice were assessed through the study of chromosomal aberrations, sperm head anomaly as against suitable untreated controls. The observations revealed that chromosomal abnormalities viz, chromosome fragment, somatic reduction, hypoploidy, hyperploidy etc. as well as abnormal sperm heads were found in pesticide-fed mice and maximum abnormalities were associated with Profenofos.
Mitotic metaphase chromosomes of Channa punctata and C. orientalis were stained with Giemsa, CMA and DAPI. Channa punctata possessed 2n=32 chromosomes whereas C. orientalis had 2n=78 chromosomes. The range of chromosomal length of C. punctata and C. orientalis was 2.70–6.60 μm and 1.50–3.00 μm, respectively. It indicates the gradual decrease in chromosomal length in C. punctata than C. orientalis. The centromeric formulae were 24m+2sm+6t in C. punctata and 34m+2sm+42t in C. orientalis. More telocentric chromosomes are present in C. orientalis, thus it possesses more advanced characters than C. punctata. Seven CMA-positive bands were found in C. punctata and 12 in C. orientalis. The CMA-positive bands in C. punctata are thicker than that of C. orientalis. Heteromorphicity in respect of CMA-positive bands was found in some homologous pairs of both the species. It reveals the probable presence of facultative heterochromatin in the non-banded homologue members. Seven DAPI-negative bands were observed in C. punctata at the same position where CMA-positive bands appeared. This reversible banding indicates that those portions of chromosomes are composed of fully GC-rich repeats. In C. orientalis, 20 DAPI-positive bands were observed. Seven DAPI-negative bands were present at the same position where CMA-positive bands appeared. This reversible banding indicates that those portions of chromosomes are composed of fully GC-rich repeats. Three chromosomes of C. orientalis showed tandem presence of GC- and AT-rich repeats. These chromosomes could easily be identified and used as marker. The 2 species possessed a distinct karyotype and therefore, could be identified authentically with these methods.
The extensive use of chemical pesticides has greatly increased the mutational load on the genome of living organisms. The problems of genetic toxicology have generated more concern than any other problem because the residual inclusion of pesticides in the environment leads to a number of direct and indirect effects on the genetic material. Induced chromosomal mutations provide a reliable index of the mutagenic potential of a chemical or a physical agent. Experience has shown that the mutagenic effect of the semilethal doses of chemicals induce a of variety of structural changes in the polytene chromosomes out of which ectopic pairings are the most frequent types of aberrations. As a consequence of these points of genetic interest, the present paper deals with the incidence of ectopic pairing of the intercalary heterochromatic bands in the polytene chromosomes of those larvae of Anopheles subpictus, which were treated with LC20 of 4 organophosphate pesticides viz. chlorpyrifos, monocrotophos, acephate and dimethoate. When compared with the data of nontreated controls the treated larvae had an elevated incidence of intercalary heterchromatic linkages in the X-chromosome and the right and left arms of autosomes 2 and 3 (2R, 2L, 3R, 3L). The results are discussed in relevance to the fact that ectopic associations are established between those heterochromatic bands which are homologous in their chemical and genetic properties. These properties are attributed to the presence of identical A : T rich nucleotide sequences resulting from gene duplications which are induced by the cellular environments altered by the pesticides.
A spatial correlation between the morphology of mitochondria and the distribution of cortical actin patches was investigated in sporulating cells of the yeast Saccharomyces cerevisiae using 4′,6-diamidino-2-phenylindole (DAPI) staining and rhodamine-conjugated phalloidin staining. In stationary-phase cells, actin patches were found to be randomly distributed throughout the cytoplasm and the distribution seemed to be independent of the distribution of mitochondria. In contrast, during the meiotic prophase, more than 60% of actin patches were located close to the strings of mitochondria, specifically at the branching or bending points of tubular mitochondria. During the first meiotic division, actin patches seemed to be present independent of mitochondria, but after the second meiotic division, significant numbers of actin patches were again present on or along the string of mitochondria that surrounded the 4 daughter nuclei. These results suggest that cortical actin patches rather than actin cables are closely involved in dynamic morphological changes in mitochondria.
The karyotypes of 21 accessions of Lathyrus L. belonging to 4 sections were investigated. Although all the species have a chromosome number of 2n=14, they could be differentiated by their karyotype formula and quantitative parameters of the karyotypes. Phenetic distance showed that in spite of the differences observed among entitied, they can be grouped in clusters that coincide with the taxonomic sections established by Kupicha and with the life cycle of the species. The section Clymenum can be distinguished by the presence of a subtelocentric pair. From an evolutionary point of view, variation in genome size, however, is congruent with morphological variation as well as with the life cycle.