An analysis of the presence of homologous association in Ornithogalum virens indicates that the homologous association reported by earlier workers may be due to the influence of some environmental factors rather than due to any inherent ability of the plant.
Tetraploids of six different varieties of Trigonella foenum-graecum were raised through treatment of seedlings by colchicine solution. Comparative studies were carried out for exploiting their useful traits. Cytology and chiasma frequency was studied in detail, Genotypic response of different varieties at tetraploid level with regard to multivalent frequency, chiasma frequency and pollen sterility shows significant differences. A natural occurring tetraploid and a hexaploid have been investigated. Problem of high seed sterility prevaling in autotetraploids of Trigonella foenum-graecum has been discussed. Appearance of heteromorphic bivalents along with fragments in mixoploid plant is a new report and its possible origin has been traced. Polyploids of Trigonella foenum-graecum are characterised by pollen shape variability while diploids have uniformly one type of grains.
Chromosomes of six varieties of Apium graveolens of the family Umbelliferae were studied, collected from different nurseries of Calcutta after evolving suitable schedules. The somatic number in all of them was 2n=22. These varieties differ in the number of chromosomes bearing secondary constrictions. One pair of chromosomes with supernumerary constrictions is missing in two varieties (Sutton's Golden Self Balancing and Verma's Golden Plume) but is present in the others. Meiotic irregularities are frequent but bivalent formation has been found to be universal, indicating that homozygosity for structural changes has been attained in these varieties through selection in cultivation. Sutton's Turnip Rooted variety with longest chromosomes might represent one of the primitive varieties.
Mean chiasma frequency at diakinesis has been studied in three intered lines of radish, namely LS-337/24, LS-337/25 and LS-43/51, their F1 hybrids and the population. It has been demonstrated that the lines significantly differ among themselves and from the original population in this character. All the lines show a marked reduction in mean chiasma frequency in comparison to the population whereas the interlinear hybrids F1 are characterized by increase of this mean which touches almost the population level. From our results it is quite obvious that the breakdown and restoration of chromosome pairing are concomitant with the mating system of the species. A genotypic control of mean chiasma frequency has been proposed in radish.
The hemispherical bottom of ordinary gelatin capsules can be softened by partial soaking in cold water. Pressing the moistened part with a smooth, flatsurfaced object will modify the original shape of the capsule to a flat-bottomed one. Plastic Petri dishes can be used for this work with excellent results. This new shape becomes stable after drying and the capsules thus obtained can be used for orientated embedment of most kinds of samples. Using these modified capsules is particularly helpful for embedding thin specimens such as cells monolayers or fungal mycelia.
Partial desynaptic plants were isolated from normal population of pearl millet (Pennisetum typhoides S. and H.) inbred T55 and mutagen (EMS and gamma-rays) treated populations of inbreds Tif23A, Tif23B and K560. The pachytene pairing was complete and normal. A variable number (2-14) of univalents occurred at MI. Anaphase I separation was normal in the majority (66-79%) of the cells; many showed 8:6 and 9:5 chromosome separation. The spontaneous desynaptic plant showed laggards and chromatin bridges at anatelophase I, while the induced ones did not show these aberrations. Chiasma frequency in the desynaptic plants was lower than that in the normal controls.
Chromosomes were identified in six radiation-induced translocations in Collinsia heterophylla in order to determine if all seven haploid chromosomes undergo breakage and reunion. Six of the seven chromosomes were involved in these translocations. The seventh chromosome not involved may be the “pseudo-supernumerary” chromosome. This work provides supporting evidence in favor of Garber's suggestion about the existence of such a chromosome in the genome of C. heterophylla.
The proximal regions of the rod-shaped autosomes and the X-chromosome of Drosophila virilis were shown to be heterochromatic. The Y-chromosome appeared to be entirely heterochromatic while the tiny dot chromosomes showed no detectable heterochromatic regions.
The satellite region of maize chromosome 6 was examined for variability of chromomere pattern at pachytene in a large number of microsporocytes. The number of chromomeres visible with the light microscope in this region was found to vary from one to five in different cells from the same plant. The two homologues of the same cell usually, but not always, matched in chromomere pattern. It is emphasized that the common assumption that pachytene chromomeres are genetically constant from cell to cell is not justified and that alternative chromomere patterns may reflect differential aggregation during condensation of subunits.
The karyotype of the Armenian hamster, Cricetulus migratorius, has been studied using trypsin-Giemsa and fluorescence banding techniques. Chromosome measurements were made on 50 metaphases and the idiogram has been constructed. The diploid number of 22 chromosomes can be identified individually based on their banding patterns, size and centromeric position. Chromosome 1 is the largest and chromosome 10 is the smallest in the complement. The X and Y chromosomes are similar in size with distinct banding patterns.
Misdivision rates of wheat chromosomes 5A, 5B, and 5D were determined at anaphase I of meiosis in F1 monosomic plants from crosses between Chinese Spring monosomics as female parents and ten Japanese local cultivars. The average misdivision frequencies were 15.3% for 5A, 10.5% for 5B, and 8.4% for 5D. The frequencies of unipolar distributions of monosomes or their derivatives were 31.7%, 34.7%, and 18.1% for 5A, 5B, and 5D, respectively. Although there was a large error variance, the differences among chromosomes and the chromosome-cultivar interactions were significant for both misdivision rates and unipolar distributions, but there were no significant differences among cultivars. The correlation (r=.554) between the frequency of misdivision in cells with bipolar distributions and the frequency of cells with unipolar distributions suggested that these traits were affected by common genetic and/or environmental factors. The female transmission of the group 5 monosomes and their derivatives averaged 12.2% for Chinese Spring. Of the transmitted monosomes, 6.9% were telocentric chromosomes, 3.4% isochromosomes, and 89.7% normal chromosomes. When the Chinese Spring monosomics were crossed with three Japanese cultivars, the transmission frequency to the F2 of the monosomes from the Japanese cultivars averaged 30%, with 9.2%. telocentric and 90.8% normal chromosomes. These results were compared with expected transmission frequencies of the monosomes and their derivatives.
Misdivision rates of wheat chromosomes 5A, 5B and 5D were determined at meiotic anaphase I in F1 monosomic plants from crosses between the group 5 monosomics of Chinese Spring and ten American (U.S.), one South American, and eleven European cultivars. The misdivision rate was usually higher for one chromatid than for both chromatids of each group 5 univalent, but in 5B from the cultivar Seneca, misdivisions involving both chromatids were three times higher than those involving one chromatid. Significant differences in misdivision rates occurred between the European (including the South American cultivar) and American groups, and also among cultivars and chromosomes within each group. 5A and 5B had similar misdivision rates, which were generally higher than those for 5D. 5A of Chinese Spring in its own background had the highest misdivision rate of any group 5 chromosome or cultivar source. The European and American groups had similar ratios of bipolar versus unipolar distributions of normally divided or misdivided chromatids. The behavior of group 5 chromosomes was compared in these two groups and in a Japanese group reported in a companion paper. Misdivision rates seemed to be affected by the specific chromosome, the genetic background in which it occurred, and possibly environmental conditions.
Cytological investigations on 30 taxa belonging to 26 species of grasses have been carried out from the hills of Kashmir. The genus Duthiea has been investigated for the first time. The species investigated for the first time are Duthiea bromoides (n=14), Helictotrichon virescens (n=14), Oryzopsis lateralis (n=12), Poa araratica (n=7) and Poa koelzii (n=14+5B). New cytotypes are reported in Alopecurus myosuroides (n=14), Festuca kashmiriana (n=21), Glyceria tongelensis (n=10) and Microstegium vagans (n=10). B-chromosomes have been found in Aegilops tauschii (n=7+1-2B) and Poa koelzii (n=14+5B).
Two cytological races having 2n=32 and 48 and designated as tetraploid and hexaploid, respectively were found in C. reflexa. While somatic chromosome complement of tetraploid race comprises of 28 metacentric and 4 submetacentric chromosomes, the complement of hexaploid races consists of 36 chromosomes with median and 12 chromosomes with submedian centromere. On the basis of general chromosome morphology and shape, the somatic chromosomes of the complement could be grouped into 8 sets, each set comprising of 4 chromosomes in the tetraploid and of 6 chromosomes in the hexaploid race. The differences observed in these parameters within the chromosomes of each set are statistically insignificant but those between the sets are significant. Meiosis in the tetraploid race is normal leading to the formation of viable pollen grains. In the hexaploid race, meiosis is highly abnormal and is arrested before heterotypic division is completed. Immediately after the pollen mother cells degenerate, branched fibrilous attachments projecting out from the degenerated PMCs are observed. When the young immature anthers were clipped off and the flowers bagged, parthenocarpic seeds are produced in the hexaploid material, However, the seed set is poor. A gene controlled suppression of homeologous pairing in the tetraploid race has been postulated. This type of control is not operative in the two hexaploid races of the species. The implications of karyotype morphology and chromosome pairing behaviour in polyploids are critically discussed in general and the role of polyploidy in the species in particular.
The cytology of the endosperm in Trad O2, a hybrid clone of Tradescantia was studied. The tissue was found to be basically triploid (3n=18). With advancing maturity higher ploid cells, mostly in exact doublings of the triploid number also were seen making the tissue mixoploid. This endopolyploidy appears to be brought about by the blockage of mitosis at very early prophase. Extensive spontaneous chromosome breakage and reunion, chromosome erosion, stickiness, spindle abnormalities nuclear polymorphism, nucleolar fragmentation etc. were observed in the degenerating endosperm and these could probably be the causes of endosperm breakdown in this natural hybrid.
Detailed cytogenetical studies in Cyamopsis tetragonoloba (L.) Taub. (=C. psoralioides DC.) have been carried out. Seven and fourteen have been found to be haploid and diploid number of chromosomes respectively. Karyotype has been analysed and found to be symmetrical type according to Stebbins (1958) classification. Inversion heterozygosity in the C. tetragonoloba has been reported for the first time. Meiotic abnormalities in the form of inversion and sticky chromatin bridges, laggards, etc. have been observed at anaphase I in about 27% cases. Pollen sterility of about 18-20% have been found to be chromosomal in nature and caused by deficiency and genic unbalance in the microspores.
In both genus, the nuclear envelope and the golgi bodies show a particular activity which is probably related to the exine depositing. This phenomenon occurs in the eraly tetrad stage. Sexine and nexine are simultaneously elaborated in Taxus. The nexine, which is constituted by strata with lamellar structure is produced by the microspore. The sexine which is only composed of sporopollenin bodies is formed outside the microspore. The exine layers of Ginkgo microspore are successively deposited: -firstly the sexine (tectum and bacula)-secondly the nexine 1-finally the nexine 2 the structure of which is similar to the Taxus nexine. Inside the longitudinal slit of the dehydrated pollen grain of Ginkgo the sexine is lacking, the only components of the sporoderm are the two nexine layers. During the germinating process the pollen tube bursts out of this thinned area of the male gametophyte.
The fine structure of an electron dense plastid inclusion, commonly called prethylakoidal body, was studied at the electron microscope level. Much like in other plants, the prethylakoidal bodies of tomato leaves occur in intermembranous regions of the chloroplast stroma and are frequently associated with grana thylakoids. The body-associated grana are closely appressed to the limiting membrane of the prethylakoidal body. The prethylakoidal bodies are highly electron dense in early stages and gradually become less dense in later stages. The interior of the prethylakoidal body appears coarsely granular. On the basis of an association between the prethylakoidal body and grana (Figs. 2, 3) and on the basis of chemical characterization (Ames and Pivorun 1974) it can be suggested that this inclusion takes part in the formation of grana.
The retinal layers of the blind cave fish, Astyanax hubbsi were studied by electron microscopy. In the pigment epighelium, myeloid bodies are present. Disoriented outer segments and short inner segments are observed. A few synaptic ribbons and vesicles are located in the plexiform layers. Large amount of glycogen particles are seen in the Müller fiber surrounding the neuronal cells.
Karyomorphological studies of different cultivated strains of three varieties of Brassica campestris L. viz. I) B. campestris var. dichotoma, II) B. campestris var. sarson and III) B. campestris var. toria obtained through the courtesy of State Oil Seed Research Station, Berhampore, West Bengal have been studied. Most of the strains show the normal chromosome number as 2n=20 and 10 bivalents in meiosis but several strains viz. I) B. S. B27, II) Y. S. T9, III) Y. S. 151, IV) Toria T11, V) Toria T81 and one local cultivated strains of toria show the aneuploid number as 2n=18 chromosomes. Such interstrain difference in chromosome number suggests the role of numerical alterations in chromosomes in the evolution of different varieties and strains of B. campestris. Intraspecific variation has been taken to show that difference in chromosome number within difference species should not be regarded as an indication of non-relationship and also confirms the possibility of their origin from a common genome. The role of minute structural alterations of chromosomes has been discussed.