Interspecific hybrids (n=18) were obtained in between S. villosum×S. americanum using higher chromosomal form as a pistillate parent and compared cytomorphologically with natural triploid hybrids. Hybrids exhibit vigorous growth with abundant flowering but failed to produce fruits in both cases. The resulting hybrids showed highly irregular meiosis with consistant presence of univalents and trivalents in the pollen mother cells. High pollen sterility indicated the dissimilarities of parental genomes due to chromosomal cause rather than genic. Triploids are originated from the union of an unreduced female gamete produced spontaneously with a normal male gamete. Results of floral parts indicates that triploid evolved from diploid populations and later by which hexaploid S. nigrum evolved.
Significant variations in chromosome morphology have been noted in eight varietal populations of Lantana camara L. and Lantana sellowiana, L. lilacina collected from different eco-habitats of India. These populations of Lantana also exhibit the existence of a polyploid series. Pentaploid L. camara L. adapt well at high altitude and temperate climate; while the diploid forms occur in plains. The evolution of this taxon has been discussed in the light of cytological findings.
The nucleus of root nodule cells of Trifolium pratense exhibits peculiar features which has been investigated by TEM. It lacks heterochromatin and possesses a penmanently individualized nucleolus-organizing chromosome. These cells perform a ribosomal gene amplification phenomenon, the nucleolar-organizing-region of the nucleolus-organizing chromosome being not only transcribed at a high rate, but it is present in double or multiple copies on the same chromosome, or on different chromosomes as a consequence of initial polyploidization process perfomed by endocycles. This process is later followed by polytenization of nucleolusorganizing chromosomes which, as a consequence, exhibit a discrete or, in some regions, an obvious banded pattern. Such genetic processes are not unexpected in these highly functionally specialized cells which are parts of the miniature “ammonia factory” represented by a functional rootnodule.
Interphase nuclear structure and heterochromatin were studied in Corchorus olitorius, Corchorus capsularis and their F1 hybrid by HCl-Giemsa and BSG-technique. Nuclear structure was chromocentric in both the parents and the hybrid. Chromocentre numbers in two species of Corchorus and their hybrid were more or less same, which were, however, found to reduce than the expected number of 14. Heterochromatin values yielded by HCl-Giemsa technique were slightly higher than those yielded by BSG treatment. The percentage of heterochromatin in F1 was found to be closer to the male parent. DNA contents were also estimated in both the parents and their hybrid but the relationship between DNA contents and heterochromatin value was not clear.
Cytological investigations on thirty three taxa of South Indian Jasminum have been carried out. Mitotic, meiotic and gametic chromosome numbers of these are determined by particulary suitable staining techniques. The somatic numbers given in the table are ascertained by comparison with meiotic and gametic numbers. A tentative scheme of cytological evolution is also given in a chart.
The meiotic behaviour, fertility and breeding behaviour of five translocation heterozygotes involving two pairs of chromosomes isolated from M1 generation of gamma irradiated population of H. muticus were studied. Pollen sterility of the translocation heterozygotes ranged from 36.8% to 68.2%. The translocation heterozygotes at MI had characteristic ring and chain quadrivalents, the former being more prevalent in four of the five translocation heterozygotes. In Translocation T-3, quadrivalent was seen associated with the nucleolus at diakinesis. Since, chromosome 4 of H. muticus is satellited and remains attached to the nucleolus, it is concluded that chromosome 4 is one of the chromosomes involved in this translocation. Alternate and adjacent orientations were equally frequent in the four translocation heterozygotes (T-1, T-2, T-4, T-5) whereas the former was predominant in Translocation T-3 resulting in reduced pollen sterility. Besides normal chromosome distribution of 14:14 at AI, 13:15 distribution and occurrence of 1-2 laggards were also observed except in Translocation T-3. The progenies from three of the four translocation heterozygotes studied segregated n the 1:2:1 ratio of normal homozygotes, translocation heterozygotes and translocation homozygotes except Translocation T-5 which deviated from the ratio due to deficit of translocation homozygotes.
Chromosome analysis of regenerants of Scilla indica (Roxb.) Baker obtained through organogenesis from leaf callus and somatic embryogenesis from anther callus was carried out. The plants regenerating from the leaf callus were all diploids whereas those regenerating through somatic embryos from anther cellus showed both diploid and mixoploid plantlets. The karyotype of the regenerants did reveal major structural changes in the diploid plantlets derived from both callus lines. In situ nuclear DNA estimation of the regenerants indicated incerase in mean DNA value only in case of a few mixoploid plantlets regenerated from anther callus via somatic embryogenesis. The nuclear state of the explant thus has an important role to play in determining the cytological status of regenerants.
Highest ploidy (2n=8x=48) was observed in S. fragrans. Meiosis of auto-octoploid showed consistent presence of multivalents in lower frequencies. Meiosis at 8n level was highly irregular with exceptionally high pollen fertility. Absence of seed setting from diploid to octoploid level concludes that some genic mechanism operating during fertilization inhibits the seed formation.
Chiasma frequency and chromosome associations at metaphase I of meiosis were studied in sixteen taxa of Hordeum viz. H. agriocrithon; H. jubatum; H. murinum; H. sativum con var. distichon var. inerme, var. nudum, con var. hexastichon var. coeleste, var. ingrum, H. spontaneum, var. agriocrithon, var. turcomanicum; H. vulgare, con var. distichon var. leiorrhynchum, var. nigrum, var. nutans, var. pallidum. All the taxa were diploids except for H. murinum which was teraploid. The diploid taxa showed regular formation of seven bivalents and tetraploid species showed the occurance of fourteen bivalents. Chiasma frequency per cell at metaphase-I varied from 14.96 to 20.08 in diploid taxa while it is 35.36 in tetraploid taxon.
The meiotic analysis in ten varieties of Lathyrus sativus clearly indicated that there was a regular formation of seven bivalents in all of them. However, they differed appreciably from each other in the number of ring and rod bivalents per pollen mother cell and the value of half chiasma per bivalent. The study of intraclass variance showed a significant variation in the chiasma frequency of different varieties. A negative correlation was noted in all the varieties except KH4 which registered a positive correlation. Such observation was indicative of the fact that there existed a variation in the distribution of chiasmata even in the same pollen mother cell. Pollen sterility was present in all the varieties but it had not attained considerable value. The meiotic data obtained from ten varieties of Lathyrus sativus confirmed that karyotype asymmetry and change in the morphology of the chromosomes were instrumental in speciation within this plant.
The modal diploid number of 44 chromosomes has been found in Mullus surmuletus and Mullus barbatus (Pisces, Mullidae). Two middle-sized subtelocentric chromosomes are involved in nucleolus organization (NORs) in both Mullus species. Despite similarity in the NOR location, valuable differences in the restriction pattern of the ribosomal genes have been observed.
Increases in frequencies of structural as well as division-disruptive changes in meiotic chromosomes and morphological abnormalities in sperm head, along with decrease in sperm count were found to be produced by the chronic administration (12 weeks, two spermatogenic cycles) of dietary concentration (0.5μg, 50±10 ppb) of crude AFB1in laboratory inbred stock of male, Mus musculus mice. These abnormalities were significantly minimised by vitamin-C, (VC) when the latter was administered in human therapeutic dose (10mg/K. b.wt./day). The concurrent and post-treatments of the vitamin were more effective in minimising the genotoxicity of aflatoxin; pre-administration of the vitamin was least effective. Scavenger role of VC in removal of biotransformed premutagenic molecules and radicals produced by AFB1has been discussed as a probable mechanism for VC-mediated minimisation of aflatoxingenotoxicity.
An yellow leaf mutant exhibiting interchange heterozygosity was located in the hybrid population (ms×960) of C. annuum. The mutant was weak and less vigorous with long narrow and yellow coloured leaves. The interchange quadruple was observed in 74.66% of cells of which the ring quadruples were more predominant compared to the chain type. The mean chiasma frequency per cell was 20.63 as against 15.72 in control plants. The tetrad stage manifested many variations such as pentads and hexads with several micronuclei in 12.71% of the cells. The progeny of the mutant plant segregated in 1:1 ratio for normal and mutant condition. The frequency of cells with interchange multiple was reduced in mutant plants of second generation. It was observed that reduction in the frequency of interchange quadruple was associated with the concommitant decrease in yellow colouration of leaves. The possibilities of association of the interchange complex with the phenotypic expression are discussed.
Mutation frequency, effectiveness and efficiency of gamma-rays, ethyl methane sulphonate (EMS) and synergistic effects of their combination treatment were assessed in T-9, an improved variety of black gram. Gamma-rays were more effective than EMS. However, EMS was 2-2.5 times more efficient than gamma-rays. There was a progressive increase in mutation frequency of chlorophyll and viable mutations with the increase in gamma-rays and EMS doses. Synergistic effects were observed for increasing mutation frequency in M2generation in combination treatment of gamma-rays with EMS.
Karyomorphology of V. vinifera cv. Gulabi, V. rotundifolia cv. James and their hybrid, revealed the somatic chromosome numbers as 2n=38, 40 and 39 respectively. In these karyotypes, 13 chromsomes pairs were median and 6 or 7 were sub-median. Total lengths of the complements were 52.78μm in James, 49.30μm in Gulabi and 51.16μm in hybrid. Gulabi had the largest chromosome (1.80μm) and James had the shortest chromosome (0.94μm). Chromosome diameter was inversely proportional to the length. All the karyotypes had only one pair of SAT-chromosomes, SAT-knob being attached to the long-arm of the chromosome. On the whole, karyotypes appeared to be symmetrical, though there are vast variations in morphology and disease resistance, suggesting the inter-chromsomel variations by way of accumulation of genic differences.
In pollen mother cells of triploid Petunia axillaris (Lam.) B. S. P. at the stage of late diakinesis some of the chain trivalents revealed an unusual form of rigidity. These are here described as “hook-shaped”, although earlier documented as ‘L’ shaped chain trivalents (Reddi and Padmaja 1979). The other point considered was whether a similar form of rigidity is also true for some rod bivalents, where the single chiasma was terminalized. Such“ paranormal bivalents” were in fact observed. The corresponding observation of hook-shaped trivalents at late diakinesis is interpreted to be a factor that could limit the frequency of alternate orientation and incidentally increase the frequency of adjacent orientation of such chains at metaphase I.
The thelytokous hybrid Bacillus whitei (2n=35, XX female) endemic to Southeastern Sicily, is clearly derived from B. rossius×grandii, but a variety of cytotypes have been found in these parthenogens. The most widespread, standard karyotype perfectly fits the suggested hybrid derivation except for the fourth metacentric element, certainly deriving from B. rossius, in which, however, nowadays invariably shows a corresponding acrocentric chromosome; on the other hand the acrocentric “modern” element has been found in hybridogenetic strains of B. whitei, very recently discovered among clonal ones. Linking together reproductive biology and geographical distribution of the “metacentric” and “acrocentric” standard karyotypes, two hybridization events between B. grandii and either a “paleo” or “neo” B. rossius, respectively, are here suggested. C-positive satellites and corresponding Ag-NOR, are found on a wide array of chromosomes, mostly reflecting those of both parental species, but also on new locations. The high dinamics of rDNA cistrons, mainly evidenced in the B. rossius genome, makes NORs not entirely reliable as long-term cytotaxonomical markers, but rather useful in short-term comparisons.
The hybrid Bacillus whitei complex clearly derives from two different interspecific hybridization events between B. rossius and B. grandii grandii. The older one gave origin to nowadays parthenogenetic clones with a “metacentric” “paleo” -karyotype, while from the more recent one originated the presently hemiclonal hybridogenetic strains, which exhibit the “acrocentric” “neo” -karyotype. These two 35-chromosome sets have been referred to as standard karyotypes. Extensive chromosomal analysis of both central and peripheral populations showed a variety of differently repatterned cytotypes (2n=35-37), all clearly derived from the“paleo”-standard karyotype. This study analyzes these cytotypes and suggests their derivation from the standard “paleo” -karyotype mainly through Robertsonian fissions of the largest chromosomes and a few heterozygous translocations. Chromosome repatterning appears to increase with the increasing distance from the Canicattini Bagni area which therefore appears to be the hybrid radiation center. The “fissionist” versus “fusionist” trend in the phasmatodean karyotypes is discussed and the particularly convincing evidence of intraspecific Robertsonian fissions of the largest chromosomes of the B. whitei set is stressed. The utilization of such fissions as unambiguous models for the molecular analysis of centromeric regions is suggested and the synthetic rDNA activity in the hybrid of both parental sets is also pointed out.
G-banded studies of the chromosome complement of the Turkish hamster (Mesocricetus brandti) reveal unique variations in the sex chromosomes and chromosome 16 when compared to previously published karyotypes. Details of the characteristics of the present mitotic karyotypes of male and female are presented.
The mutagenic effect of tubercule bacilli, M. tuberculosis culture in treated male parent mice was assayed by bone marrow chromosome aberrations, first spermatocyte chromosome aberrations and sperm head abnormality and the same along with chromosome aberration in embryonic liver and MNT in F1 after mating treated male parents with normal virgin females, and by bone marrow chromosome aberrations, MNT and sperm head abnormality in F2 individuals obtained by pair mating of F1 treated series. As compared to controls, each test was found significantly high indicating the mutagenic potential of M. tuberculosis in treated mouse system assuming that the treatment induced mutation to some locus/loci of some chromosome which had pleurotropic effect and was transmitted from male parent to F1 progeny and from F1 to F2 generation by pair mating of F1 treated series. While the cytogenetic effects assayed here on living F1 and F2 progeny, the results of lethal test have been presented in another paper. Since the mutagenic potential of M. tuberculosis to parent and F1 and F2 generations of mice was found, it would have implication to mankind because the genotoxic potential of M. tuberculosis has been found in T. B. patients.
Mitotic and meiotic chromosomes from the gonads of the freshwater gastropod, Lymnaea luteola Lamarck, family Lymnaeidae have been studied. The 2n=34 and n=17 were confirmed from the spermatogonial and meiotic metaphases respectively. All the chromosomes were found biarmed with median or submedian position of their centromeres. Allocycly has been observed among the chromosomes at different meiotic stages. The differences in the morphology of the chromosomes of the same species reported earlier have been pointed out. Chromosome number conservatism at the confamilial and congeneric level of the order Basommatophora with the tendency towards an increase in the chromosome number have been discussed.
Three types of commonly used hair dye components, 4-amino-2-ntirophenol; 1, 4-diamino-2-nitrobenzene and metaphenylene diamine were treated to male mice for detection of gross chromosomal abnormalities follwing the bone marrow micronucleus test. All the test compounds were found to be clastogenic. The study also addressed the high toxicities of nitrophenol, nitrobenzene and phenylenediamine dyes and immediated attention should be given arresting their application for environmental homoeostasis.
Treatment of Alium cepa seeds with different concentrations of Methyl parathion (insecticide) and Tri-miltox (fugicide) induced different types of chromosomal aberrations, such as micronuclei, chromosomal fragments, laggard chromosomes, single and multiple bridge formation. Maximum number of cells were observed with micronuclei, then with bridges and the minimum with laggard chromosomes. Methyl parathion produced comparatively more chromosomosomal aberrations than Tri-miltox. Comparing the three treatments applied, seed treatment produced maximum chromosomal aberrations, and the root treatment with recovery period produced the minimum chromosomal aberrations with the root treatment occupying the intermediate position.