1. The frequency and distribution of chiasmata in five Trillium species has shown that, in American species, pairing and chiasma formation starts near the centromere, then, in suitable conditions, again at the distal end and finally continues to the median region of the arm. In the Japanese species, T. kamtschaticum, only the proximal chiasmata are usually formed. 2. Confirmation of this sequence was provided by the proximal localisation of chiasmata induced when pairing was interrupted by a heat shock. As the frequency of chiasmata decreased, the degree of localisation increased. 3. Chiasma frequency in one individual of T. grandiflorum revealed no interaction between bivalents, Variation in all whole chromosomes and most individual arm is random. 4. A positive correlation of chiasma frequency occurs between B and D short arms, the two in which chiasma formation occasionally fails altogether. It is suggested that this correlation is due to the effect of the fusion of their chromocentres on the procentric pairing of these arms. In other species where these same arms contain long H-segments, chiasma formation also frequently fails.
1. A cytogenetic study of the members of the Bothriochloa intermedia was made from several geographic locations of the world. The most common chromosome number was 2n=40, however, plants with 2n=50, 60, and 80 chromosomes were also encountered. B. longifolia which is very closely related to B. intermedia has 2n=20 chromosomes. 2. Presence of univalents, bivalents, trivalents, quadrivalents, bridges, and fragments at meiosis indicate hybridization as well as chromosomal interchanges. The plants behave as segmental allopolyploids. 3. Aneuploids though present in the artificially produced populations are absent in the natural populations, indicating a lack of survival in nature in competition with plants having complete genomic constitution. 4. Polyploid B. intermedia complex is widely distributed in the tropics and sub-tropics of the world, and shows a greater ecological plasticity than the diploid relatives which have restricted geographic and ecological distribution. 5. Polyploidy in the B. intermedia apparently is due to large scale hybridization made possible through apomixis and preferential pairing of chromosomes. B. intermedia is another group where apomixis is correlated with polyploidy.
The effects of commercially available nucleic acids, their salts or their precursors added to a culture medium on the mitotic activity of cultured cells of Vicia faba under liquid shaking conditions have been reported. The addition of intact DNA or RNA to the control medium did not reveal any considerable effect on the growth rate of the cell aggregates whereas the addition of sodium salts of DNA or RNA at low concentration of 0.1% showed a very significant stimulatory effect on the percent of mitoses in the cell aggregates than in the control. Analysis of variance made on the 24 hour mitotic percent data using an orthogonal contrast method indicated that the difference between the two nucleate treatments was not significant; but each was highly significantly different from the control. At high concentrations of 0.5% or 1.0% DNAate in the medium, although the cells usually showed a complete cessation of mitoses in the beginning, after 4-5 days, the cell aggregates recovered revealing actively growing bud-like outgrowths from the original inoculum. Further incubation in these high concentrations did not appear to inhibit growth. Cell aggregates growing in medium containing the nucleates or nucleic acid precursors (cytidine or uridine) also revealed an appreciably high incidence of polyploid cells in division. This was particularly pronounced in cell aggregates growing in medium containing DNA, DNAate, cytidine or uridine. The present study thus reveals the heterogenity of cell types present in V. faba tissue cultures and the selective effect of growth factors on the mitotic pattern of different cell types. It is suggested that such evidences like stimulation of division in polyploid cells and recovery of mitotic activity following high concentrations of nucleic acid salts may be the result of certain stimuli brought out by the chemical additive incorporated in the culture medium. Specific cell types are thus stimulated to undergo division and express themselves as part of the cell population. The possibilities of using these techniques in studying interactions between the genetic potential of cells and the environment (chemical) to which they are exposed is suggested.
Morphological changes occurring in cells of the mouse testis treated in hydrogen ion concentrations from pH 3.0 to 7.5 have been studied with the phase contrast microscope and in fixed-stained preparations. Living cells were prepared by techniques involving use of pressure and without pressure. The pressure technique was more advantageous for studying living cells. Many cells undergoing spermatogenesis produced pseudopodia which moved and grew in all media except that adjusted to pH 3.0. Blebs and bubbles occurred on cells treated at pH 4.0 to 6.0. Granulation of nuclei, which became more pronounced in solutions of greater acidity, was also observed. Cells at strongly acidic hydrogen ion concentrations clumped together and the membranes dissolved, leaving only clumps of chromosomes intact. Extreme shrinkage of cells occurred at pH 3.0. Pseudopodia, bubbles, or blebs were not observed in fixed-stained preparations, but dissolution of cells with subsequent freeing of chromosomes occurred at strongly acidic pH values. Granular droplets resembling secretory products were observed when cells were treated at high hydrogen ion concentrations.
The recessive mutant ft (2L at 12.0) contains vacuolae in the cells of larval salivary glands. In the chromosomes of these cells a puff is formed in region (24D/E) corresponding to the locus of the gene ft. This puff appears or disappears as the vacuolae are present or absent. There are also secondary puffs in other chromosomes of ft/ft larvae, this indicates an interaction between ft and other loci of similar activity.
The diploid chromosome number of L. lacca is eighteen in both sexes. Males of L. lacca maintain, from an early embryonic stage, one hap. loid set of chromosomes in a condensed form and this heterochromatic set later on at second division develops a monopolar spindle and reaches the other pole of the spindle. Cytoplasmic division is suppressed and this results in the formation of binucleate spermatids which later fuse to form the quadrinucleate spermatids. The spermatid nuclei formed by the chromosomes of the heterochromatic set degenerate while those formed by the euchromatic set give rise to typical coccid sperms.
Some cytological effects of an alkylating agent, apholate, a commonly used chemosterilant, on the Rock strain of Aedes aegypti were studied. Two to four days old larvae were reared until pupation in 10ppm apholate. Mitotic chromosomes were studied from squash preparations of larval brains stained with acetolactic orcein. Apholate induced numerous chromosomal aberrations by virtue of its ability to break and physiologically modify chromosomes. Among the chromosomal aberrations observed were stickiness, deletions, ring chromosomes, dicentric chromosomes and anaphase bridges. Chromosome breakage appeared to be frequently induced in the region of the secondary constriction in one of the larger chromosomes. Also, treatment with apholate resulted in the induction of somatic tetraploidy in some brain cells. It may also interfere with normal replication of chromosomes. Explanations for the induction of these aberrations have been discussed.