Shortening Of Chromosomes Research Articles

CHANGES OF CHROMOSOMES DURING THE EARLY NEURAL DEVELOPMENT OF A JAPANESE NEWT, CYNOPS PYRRHOGASTER.

The karyotype of Cynops pyrrhogaster was determined on the mitotic chromosomes in the presumptive neural area of an early gastrula. 24 chromosomes of a diploid set consisted of 8 metacentric and 4 submetacentric pairs. Individual chromosomes were identified on the basis of their morphology and characteristic C-binding patterns. Sex chromosomes were not identified. Total length of the haploid chromosome set in the presumptive neural area decreased remarkably from morulae to gastrulae, further continued to decrease up to neurulae and thereafter remained unchanged till tail-buds. Chromosome shortening occurring from morulae to gastrulae was accompanied with a prominent decrease in chromosome volume, keeping chromosome width constant. Shortening took place evenly along the longitudinal axis of a chromosome. When gastrulae and neurulae were compared concerning their positions of the appearance of the C-bands, the basic pattern remained unchanged. In certain chromosomes, the number of C-bands decreased as the result of their fusion, as gastrulae proceeded to neurulae.

Comparative study of the function of polytene chromosomes in laboratory stocks of Drosophila melanogaster and the l(3)tl mutant (lethal tumorous larvae). II. Changes of banding pattern and transcriptional activity in the salivary chromosome of l(3)tl.

The salivary chromosomes of the l(3)tl mutant of D. melanogaster are considerably thicker and shorter than those of normal larvae. In most nuclei, chromosome shortening is associated with morphological changes of two types. a) The bands lose their distinctive pattern and become loose. The chromosome appears as a granular mass. In extreme cases pompon-like chromosomes arise. Most frequently male X-chromosomes undergo such changes and begin to shorten as early as in the middle of third larval instar. "Pompon" transformation is not associated with a change in the relative intensity of RNA synthesis: the ratio of silver grain number over the male X-chromosome to that over regions 61A-63F is the same in pompon-like l(3)tl chromosomes and in the male and female X-chromosomes of the normal lines. b) Shortened chromosomes occassionally retain distinct band organization and, in these cases, chromosome shortening is observed to be due to the condensation of the chromatin of many puffs and interbands resulting in the fusion of a large number of bands into "new" chromatin blocks. In regions of fused bands, transcriptional activity is decreased as compared with regions where this union does not occur. The chromosomes of l(3)tl larvae lack ecdysone-stimulated puffs and other prominent puffs. In 144-192 hour larvae, puffs can be induced by ecdysone and until 384 hours by temperature shock. The capacity of puff induction decreases with larval age.

The Karyology ofClavelina LepadiformisMueller (Ascidiacea)

SUMMARYThe embryonic mitosis of Clavelina lepadiformis is characterized by the presence of precociously separating daughter kinetochores and by an extreme shortening of chromosomes during prophase and prometaphase. The chromosomes of Clavelina lepadiformis are all metacentric; differentiated sex chromosomes are not present. The same haploid number of chromosomes, n=9, has been found in both populations of the Lagoon of Venice and of the west coasts of Scotland. Both oocyte and spermatocyte bivalents possess chiasmata.

Sorghum Pachytene Karyotypes

Sorghum [S. bicolor (L.) Moench] pachytene chromosomes show considerable detail in morphology. Previous reports have characterized karyotypes. In the present study, karyological observations covered a wide range of sorghum germplasm. Most collections were found unsatisfactory for karyotype analysis. Of those which were satisfactory, exhaustive simultaneous comparisons of chromosome lengths, arm ratios, and other morphology could not establish any complete karyotypes. Of the ten chromosome pairs, however, one nucleolar pair and one asymmetric pair were easily identified. A group of three longer pairs could be distinguished from five shorter pairs. Beyond this, it did not seem that complete karyotypes could ever be obtained, in view of the large length variation computed for the two identifiable chromosomes. This variation could not be entirely assigned to hypotheses of chromosome shortening or to any feature of the technique, though each step of the technique was analyzed for its reliability. The nonconformity of the present results from those of previous reports challenges the repeatability of the previous experiments. This, in line with statements by some sorghum workers, suggests that the basic karyology of sorghum is not well understood. Sorghum bicolor (L.) Moench (Gramineae) includes the grain sorghums, cultivated widely in many of the world's developing regions-in much of Africa, and parts of India and China. Sorghum is thereby one of the six great staples in the human diet along with rice, wheat, cassava, maize, and the potato (Brown, 1963: 32).

Induction of Mitotic Abnormalities in Certain Genera of Tribe Vicieae by Paradichlorobenzene

Effect of paradichlorobenzene on somatic chromosomes of Vicia faba, V. narbonensis, V. hirsuta, Pisum arvense and Lathyrus sativus was studied after giving a prolonged treatment. Various mitotic anomalies were encountered. These included shortening and thickening of chromosomes, precocious separation of chromatids, tetraploid cells, binucleate cells, chromosome bridges and chromosome breakage. The potentiality of PDB as a mutagenic substance had been emphasised and terms like PDB-treatment, PDB-mitosis and PDB-metaphase were suggested for convenient use. Chromosome breaks generally took place at the heterochromatic regions.

Chromosome preparation from fresh and cultured tissues using a modification of the drying technique.

TECHNIQUES for making satisfactory chromosome preparations have evolved rapidly during the past decade since Makino and Nishimura1 and Sachs2 adopted pre-treatment with hypotonic solutions and the squash method of preparation. Administration of colchicine increased the number of countable mitoses and facilitated analysis by arresting cell division in metaphase, producing shortening of chromosomes and divergence of sister chromatids.

The Effects of Aldrin, Dieldrin, Isodrin, Endrin and DDT on Mitosis in Roots of the onion (Allium CepaL.)

Experiments were carried out with aldrin, dieldrin, isodrin, endrin and DDT to ascertain whether, employed as insecticides, these compounds had any effect on cell division in onion root-tips. The doses used were equal to, or greatly in excess of, the recommended rates of application. By germinating onion seeds in direct contact with the insecticide under investigation, it has been shown that none of the compounds had any effects on germination or growth rate. High doses of aldrin, dieldrin or isodrin had a slight toxic effect on the resting cell, which, with aldrin, was also caused by the recrystallized compound. Aldrin and dieldrin had no effect on the dividing cell. Isodrin and endrin caused slight stickiness between chromatids in anaphase, which was insufficient to prevent the completion of division in the cell, and DDT caused a delay in the early stages of prophase and a shortening of chromosomes in metaphase.Pot experiments, with high doses of each compound, showed that germination and growth rate we...

Expulsion of the sex chromosome from the spindle in spermatocytes of a mantid

1. In the primary spermatocytes of the mantid Humbertiella indica the separation of the centers during late prophase is accompanied by corresponding movements of the nuclear membrane. Center and membrane thus remain in close juxtaposition suggesting that some form of attraction operates between them. 2. Interpolar distances are subject to a series of changes definitely associated with the successive mitotic phases. At the initiation of spindle formation the distance between the centers is large; it decreases sharply until metaphase; then remains constant until mid anaphase; and progressively increases to an extreme degree during late anaphase and early telophase. 3. At first metaphase the autosomal bivalents orient in a typical equatorial plate, but the X chromosome lies out in the cytoplasm, spatially separated from the spindle body by a wall of mitochondria. 4. Expulsion of the X chromosome from the spindle is correlated with a delay in its kinetochore-center interaction. 5. The anaphase movement of the autosomes is associated with a progressive shortening of the chromosomal fibers during the entire anaphase, accompanied during late anaphase by an elongation of the spindle body. But in the case of the X chromosome shortening of the chromosomal fiber occurs only during late anaphase. 6. Subsidiary conclusions on the cytoplasmic origin of the chromosomal fiber of the X, the relation of the bouquet stage to the double polarization of late prophase, the non-chiasmate structure of the autosomal bivalents, and the absence of the premetaphase stretch stage are recorded.

Die Beeinflussung der Mitose durch Urethan

2% aqueous solution of urethan causes after 6–10 hours' action on root types ofVicia faba andAllium cepa a shortening of chromosomes, it stops also the metaphase and lowers the rate of mitosis. Probably there is a connection between the lipophile groups, the reduction in surface tension, and the diminution of chromosomes. Dioxan with similar physical properties has the same effect.