The salivary gland chromosomes of Anopheles tessellatus are described and figured. The complement consists of a subtelocentric X chromosome with one very short arm, and two metacentric autosomes. No homologies in banding pattern with other members of the subgenus Cellia are apparent.
A system of chromosome classification based on arm ratio has been proposed to enable the cytologists to determine precisely and describe accurately all the known centromere locations. Median (M), submedian (SM), subterminal (ST) and terminal (T) have been considered as fixed point positions while, nearly median (nm), nearly submedian (nsm), nearly subterminal (nst) and nearly terminal (nt) are the four intermediate regions of these four fixed point positions. A table embodying nomenclature, notation, centromere location and the arm ratio values-R1 as short arm/long arm and R2 as long arm/short arm has been represented to serve as a ready reckoner for chromosome classification. The advantage of the present system has been discussed in the light of other systems which were erected arbitrarily for specific materials to meet specific needs.
Meiosis was regular in two chromosomal races of Iseilema laxum Hack. with n=14 and n=15 chromosomes. Pachytene chromosomes have similar morphology in the two races. They could be identified from their differential staining reaction, position of centromere, absolute length, presence or absence of prominent chromomeres and nucleolus attachment. The first 14 chromosomes in race 1 were similar to those of race 2. The F1 of the two races has 14 II and 1 I and meiosis was regular except for the univalent. The genomes of the two races are homologous except for the presence of an excess pair of chromosomes in race 1. The extra chromosome is not a B-chromosome as was evident from its morphology and cytological behaviour. It was concluded that chromosome 15 of race 1 does not carry any vital genes or alternatively, the two races may be allopolyploids or secondary polyploids derived from closely related species in which loss of a single chromosome pair may not have serious affect.
500 selfed seeds of the tetraploid Ageratus conyzoides Linn. (monsoon ecotype) were treated for 48 hours with a saturated solution of aesculin (6-B glucoside7-hydroxy coumarin). Out of 13 emerging seedlings only 4 survived and exhibited morphological gigas, reproductive diminution, pollen abortion, style degeneration, and total seed sterility. These plants on analysis revealed a disturbed course of meiosis, non viable gametes and seed sterility in both the selfed and crossed floral heads. The manifestations of abnormal meiotic events and their genetic implications are discussed.
In the present paper a salivary gland chromosome map of Anopheles barbirostris var. ahomi, inhabitant of Upper Assam, has been constructed and described in detail. This form resembles very closely with A. barbirostris (Chowdaiah et al. 1970) both phenotypically and cytogenetically but there have been observed a few significant differences in the banding patterns of the salivary chromosomes of the two forms.
Variation in meiotic behaviour was analysed in accessions belonging to four chromosomal races (2n=36, 44, 54 and 56) in two species of Cenchrus. All the accessions possessed the same chromosomal irregularities during the process of meiosis. The aberrations encountered were essentially of the same kind, but their frequencies were dissimilar in different accessions. These irregularities were the presence of univalents and multivalents, lagging chromosomes and chromosome bridges at anaphase I, laggards at anaphase II and numerous micronuclei at both the dyad and tetrad spore stages. These are commonly associated with polyploidy and hybridisation and both the factors are involved in the evolution of the complex. Evidence from chromosome associations points to the allopolyploid nature of the chromosomal forms and the segmental homology of the duplicated genomes.
Lens nigricans, a rare species of lentil possess a somatic chromosome number of 14 (2n). The somatic complement comprises of 4 pairs of median chromosome, out of which one pair bear satellite. The secondary constriction is very near to the primary constriction. This type of SATELLITE has been termed as “Intercallary trabant” by Darlington (1965). The meiotic system is highly irregular in this species. Formation of univalent, multivalents, chains, rings, bridges and laggards has been recorded. The meiotic chromosomes shows asynaptic behaviour, which may be the outcome of various types of exchanges between chromosomes or it may be due to change in the behaviour of the gene concerned. From the present investigation it appears that L. nigricans has not acquired stability as yet and translocation has played an important role in its evolution.
Cytomorphological behaviour of two desynaptic mutants obtained by gamma irradiation of barley seeds of var. K 12 have been discussed. The partially desynaptic mutant had normal morphology while desynaptic mutant was semi-dwarf and conspicuous because of the failure of its spike to come out of the flag leaf. Both the mutants were sterile. Chromosome behaviour at meiosis shows varying degree of univalents at metaphase I. Partially desynaptic mutant showed from 2 to 6 univalents while desynaptic mutant had 8 to 14 univalents. 70% cells in this plant showed complete desynapsis. A completely random chromosome disjunction was found at anaphase I, together with lagging of chromosomes. At M II several abnormalities were found as a consequence of previous desynapsis and irregular polarisation.
Nuclear area of outer epidermal cells of white onion bulb scales was 55% of those of inner epidermis (3.80×10-6cm2 compared to 6.92), dry mass per unit area was 71% of that in inner epidermis (9.67×10-5g/cm2 compared to 13.57), and nuclear dry mass was 40% of that of inner epidermis (3.71×10-10g compared to 9.29). We conclude that although they have a common origin, the cells of these tissues are morphologically, cytologically, and physiologically different.
A sterile plant of Trigonella foenum-graecum having bushy habit was isolated from C1 colchiploids in late season. This plant was diploid as revealed by petal tip squashes and its anthers contained disintegrated sporogenous tissue indicating male sterility. Gynoecium was normal. Results of efforts of artificial pollination and possible mutagenic effects of colchicine have been discussed. The authors are thankful to Prof. S. C. Agarwala for laboratory facilities and to Dr. (Miss) Sheila Joshi for help.
The partial sterility of the mutant was due to desynaptic condition which was governed by a single recessive gene. Besides the lack of chiasma formation and the presence of univalents, the cytological studies of the mutant revealed several other abnormalities, such as, the clumbing of chromosomes at MI, a high frequency of laggards in both the meiosis I as well as II which usually formed the micronuclei in the dyads and the quartets respectively. The desynaptic plants produced 43.9±1.54 (n=9) and 63.0±0.8 (n=15) percent stainable pollen grains and 12.5±1.5 (n=11) and 34.4±1.0 (n=15) percent seed set under the growth room and field conditions respectively. The possible use of the mutant in the studies of mechanism of chromosome pairing and crossing over and in the production of aneuploids has been indicated.
Study of meiotic behaviour of maize haploids revealed the presence of intrachromosomal duplications which are manifested by fold-back pairing of distal segments or of whole chromosomes. Interchromosomal duplications, though to a much lesser extent, were also suggested from the results. In a study of 350 cells at metaphase, associations were ten univalents in 63.43 percent, eight univalents and one bivalent in 31.14 percent, and six univalents and two bivalents in 3.72 percent cases. Tri and pentavalents were also observed in few cells. Most of the bivalent configurations in dia-metaphase were considered to be pseudo-associations resulting from apposition of heterochromatic segments of two heterologous chromosomes. Bivalent formation appeared to be non-specific, among different members of the complement, and there was also a preponderance of end-to-end associations. Bivalent associations were found to persist through late anaphase. Anaphase distribution was random and segregation of chromosomes to poles followed the expected pattern. It is suggested that modern maize is not an alloploid and the haploids studied represented true monoploids with intra and possibly interchromosomal duplications.
In autotetraploid of jute (Corchorus capsularis) coefficient of realization of quadrivalents was found to be very high (0.75). A PMC on an average found to contain 0.77 univalent, 2.56 bivalents, 0.35 trivalents, and 5.26 quadrivalents. All types of quadrivalent configurations were observed of which figure of eight were most frequent (24.59%). Chiasma frequency per chromosome were found to be 0.97 and 0.93 in diploid and tetraploid respectively.
The morphological feature of the nucleolar constriction was studied in the chromosomes of generative nuclei in the following twelve species of Angiosperms: Narcissus jonquilla, Tradescantia paludosa, Brodiaea unfora, Hemerocallis thunbergii, Allium fistulosum, Impatiens balsamina, Lotus corniculatus, Pedicularis resupinata, Salix gracilistyla, Thea sinensis, Hordeum vulgare and Aster scaber. In all of the species studied, except for Allium fistulosum, the nucleolar constirction which is a structural characteristic of the nucleolar chromosomes of the respective species was found to be absent in the chromosomes of the generative nuclear division in pollens. The absence of the nucleolar constriction was confirmed by the observation of dinuclear and trinuclear pollens.
1. The tannin body begins to appear as a radiated structure in the early stage of development. Such a structure of the tannin body seems to be resulted from that the origin occurs at the region where the several cytoplasmic strands running across the central vacuole fuse each other to form a radiated shape. 2. Each thread of the radiated structure grows thicker, and the radiated shape of tannin body becomes somewhat star-like. 3. The star-like structure develops into a spherical body in the middle stage of the development. Following three layers are distinguished in the typical body: a) a central layer which seems to be composed principally of tannic substance, b) a layer enveloping the central layer, perhaps having special property of cytoplasm, c) a membrane-like layer accumulating tannic substance and covering the body. 4. The spherical tannin body becomes a massive appearance at the latter stage of development. 5. A part of the tannin body is in contact with parietal cytoplasmic layer. 6. It is suggested that the tannin body in the rose petals superficially resembles the tannin vacuole in the motor cell of Mimosa pulvinus.
A study of the male meiosis in seven species of cotton rats, genus Sigmodon, was carried out. The general course of meiosis in four species, S. hispidus, S. leucotis, S. ochrognathus, and S. alleni, is similar to that in other mammals studied. In pachynema, the sex bivalent is negatively heteropycnotic and tightly coiled to form the sex vesicle. In diakinesis, the sex bivalent is elongated and stains lightly. All of these species have a diploid number of 52, and 26 bivalents are seen in diakinesis. In the remaining three species, S. arizonae, S. mascotensis, and S. fulviventer, the sex bivalent is negatively heteropycnotic in pachynema with no indication of condensation. It would appear that the functional activity of the sex chromosomes in meiosis in these species is completed before pachynema. Diakinesis stages in S. arizonae (2n=22, 24) possess 11 or 12 bivalents; in S. fulviventer (2n=28, 29, or 30) 14 or 15 bivalents; and S. mascotensis (2n=28) 14 bivalents. Differences found in activity of the sex bivalent can be correlated with the two groups of Sigmodon established on the basis of diploid and fundamental numbers and represent another expression of the differences in genomes between the two groups.
Cytology of 23 taxa belonging to 9 genera of the family Amaranthaceae were studied. Of these, chromosome numbers for six taxa viz. Amaranthus hybridus L. var. frumentaceous Roxb., A. caturtus Heyne., Allmania nodjora Br. var. roxburghii Hook. f., Celosia pulchella Moq., Pupalia lappacea Moq. and Cyathula prostrata Bl. were recorded for the first time and different chromosome number has been recorded in each of the two species viz. Amaranthus giganteus Koenig. and Allmania nodiflora Br. against the previous reports. All the reports of chromosome numbers by earlier workers were compiled along with our own. In the light of the cytological findings the taxonomic positions some members of the family were discussed. The cytological analysis indicated that the genus Amaranthus L. was characterised by greater amount of homogeneity in its chromosome numbers than other genera of the family. Basing on Grant's (1969) view that the basic chromosome number of x=17 is a probable derivation from x=16, two lines of evolution from this basic number in the cytological level was visualised; one through euploidy resulting n=32 in few species and the other through aneuploidy resulting n=17 in larger number of species.
Microsporogenesis and anther development in Iphigenia pallida Bak. were investigated using the cytochemical staining methods for the demonstration of insoluble polysaccharides, RNA, proteins and DNA. The insoluble polysaccharides and proteins are at low level in sporogenous tissue and PMCs. Both of them gradually increase in dyads, tetrads and microspores. Large number of starch grains appearing in the-vegetative cell of the young 2-celled pollen grain disintegrate and form densely PAS positive cytoplasm in the shedding pollen grain. A protein and PAS positive layer deposited internally around the PMCs at the beginning of meiosis, disappears prior to the separation of microspores from the tetrads. The cytoplasm of PMCs, dyads, tetrads, microspores and pollen grains is rich in RNA. The nucleus of the generative cell is more Feulgen positive than that of the vegetative cell. The tapetal cells have rich RNA and considerable concentration of proteins as well as polysaccharides. The fibrous endothecial thickenings are lignified.
The cytochemical studies of vitellogenesis in Oxya velox establish the following facts: 1. The Golgi bodies are clearly involved in the formation of fatty yolk which, however, consists predominantly of triglycerides with traces of phospholipids. 2. The compound yolk originates from the follicular epithelium and is composed of carbohydrates (1:2 glycol group and glycogen) and different groups of protein.
Role of nucleic acids and insoluble polysaccharides in the tissue differentiation was studied on the anther tissue-sections of Zea mays L. using light microscope. The results obtained were discussed in the light of available reports in this regard. Archesporium and sporogenous tissues are characterized by rich RNA content. RNA quantity is reduced very much in PMCs and the meiotic derivatives. Young anther wall layers, as they differentiate centripetally, show rich RNA content which is reduced as they grow older, at the periphery of the anther locule. Tapetum since its inception is rich in RNA and maintains this quantity until it disintegrates. It is so even in the tapetal cells differentiated from the connective by dedifferentiation. DNA concentration in the early sporogenous tissue is high, resembling primordial tissues surrounding it. In successive growth phases, DNA quantity is reduced to a faint level in the tissue, but, however, increases in PMCs prior to meiosis. The tapetum remains rich in DNA. The cytoplasm of sporogenous tissue shows faint PAS-positive tinge and at no stage starch was recorded in this, PMCs and haploid spores, but tapetum contains PAS-positive grains until meiosis is over. PAS-positive additional wall is formed around PMCs which persists until the completion of meiosis. Anther wall layers are rich in starch storage. Rich starch storage in endothecium is of specific importance, as it contributes to the differentiation of endothecial thickenings in the mature anther. The insoluble polysaccharides occur in anther tissues in the form of additional PAS-positive thickening around PMCs-a “molecular filter” (Heslop-Harrison, 1964), endothecial thickenings and starch, a primary source of energy. Therefore, they greatly contribute to the histochemical differentiation of anther tissues.
A modification of several leucocyte culture techniques and additional improvement in the components of the culture medium has provided an easier and more successful method for rabbit chromosomal preparations.
1. According to the atractoplasm theory, the cause of carcinogenesis is ultimately attributed to a deficiency of SFR genes which give information to repress the spindle formation for the cell differentiation. 2. This deficiency of SFR genes takes place as a result of somatic cell mutation induced by DNA recombination errors. 3. All the agents and the treatments, and also the cells attacked by viruses, all of which heretofore have been considered to be the causes of carcinogenesis are nothing but the causes inducing cell conditions under which various grades of DNA fractions would appear in the disintegrated nuclei of wounded cells. These DNA fractions permeating into neighbouring mitotic cell nuclei of wound-healing tissue participate in giving rise to DNA recombination errors. 4. Among various kinds of mutant cells induced by recombination errors, those cells encountered having a deficiency of the SFR genes by chance become incipient cancer cells or stem cells. 5. The genomes of the stem cells, the tumor cells and the tissue cells of tumorbearing organs are the same, but the first two cell groups have a deficiency of SFR genes. 6. Corresponding to the increase of a vast number of cells in growing tumors, the morphology and the metabolism of the tumor cell groups alter conspicuously, and the kinds of genes in active or dormant states alter as well. Accordingly, many newly produced substances appear differing from those in tumor-bearing organ tissue cells, as well as from those in incipient cancer cells. Therefore, various immunological reactions found in tumors imply neither the evidence for the presence of cancer-specific substances nor that for a plurality of cause for carcinogenesis. 7. The only cancer-specific substance which should be determined immunologically and isolated biochemically is logically the substance which may be produced as a result of a deficiency of SFR genes.