The chromosome number of 11 species of Australian tettigoniids, (Orthoptera-Tettigonioidea) are reported in this paper. The main characteristics of the karyotype of these species are given in the following table. In Polichne parvicauda (specimen no. 6) and Caedicia marginata a centric fusions between the former X and a small autosome was found. These fusions gave rise to a neo-XY sex-determining mechanism in both species. Besides, two centric fusions between autosomes occurred in the former species, forming two pairs of metacentric chromosomes and reducing the chromosome number to 2n=16. In Torbia viridissima a reduction to 2n=19 due to an integration of chromatin between apparently two small autosomes took place. The desynchronized movement of the chromosomes during first anaphase due to their bimodality in length as well as the difference in chiasma frequency was discussed.
The extent of increase in bivalent chiasma frequency associated with varying degree of asynapsis was examined in several inbred lines, one openpollinated variety and one single cross hybrid of maize. Differences observed among lines were interpreted as indicative of genotypic control of compensating chiasma formation. Inbred lines showing high and low degrees of compensation could be recognised.
The mutational responses of the A1-Dt system in maize to a chemical mutagen, namely maleic hydrazide (MH) was studied in material homozygous for the highly mutable (Dt-responsive) αm1 allele, as a part of a comprehensive study aimed at understanding factors concerned in the stability (or conversely high mutability) of genetic elements. A two-fold action of the mutagen could be recognized: (1) one manifested in a reduction in the number of coloured (A1) spots-each presumably resulting from a somatic mutation of αm1 to A1 in the presence of the non-allelic Dt gene; and (2) the other expressed as an increase in the average as well as maximum length of coloured spots. The former is probably due to the loss of the Dt gene (chromosomal aberration) and the latter due to more frequent early somatic mutations. The use of the αm1-Dt system for distinguishing between different effects of a mutagen was suggested.
The effects of o-nitrophenol, p-nitrophenol, p-chlorophenol, 2, 4-dichlorophenol, pentachlorophenol, α-naphthol, β-naphthol, and 2, 4-dichloronaphthol were studied on root mitosis of Vicia faba. o-Nitrophenol, p-nitrophenol and α-naphthol simulated colchicine in its effect on the mitotic stages, so they caused accumulation of the metaphase stage on the expense of the anatelophase stage. The effect of phenols on the percentage of anomalies induced in the mitotic stages, as well as, their effect on the mitotic indices of Vicia faba were found to be proportional to concentration. All the phenols tested affected a considerable decrease in the mitotic index when compared with the control. The induced types of anomalies were: disturbed type (disturbed metaphases, prophase-metaphases and disturbed ana-telophases); lagging chromosomes; stickiness; fragmentation; and cytomixis.
Comparative cytohistological studies were made of shoot tips of Equisetum hyemale, Picea abies, and Prunus Persica, as examples from three major taxonomic groups of plants: lower vascular plants, gymnosperms, and angiosperms. The purpose of this study was to find out more specifically what factors determine the formation of apical histogenic layers. Obviously the plane of mitotic division in the cells at the upper surface of shoot apices determines the presence or absence of apical cell-layer formation. The hypothesis proposed is that the plane of mitotic division-positioning of metaphase chromosome plates-in cells in the surface region in shoot apices is determined by: 1) size of cells relative to shape and size of apical dome; 2) size of cells and space in cells relative to size of their nuclei and the freedom of their nuclei from wall pressure; and 3) location of cells and their shape and availability of space across a particular plane in cells in which metaphase plates can be accommodated. The hypothesis would explain the general predominance, or presence, of histogenic layers in shoot apices of angiosperms and relative paucity or lack of them in shoot apices of gymnosperms and lower plants.
1. The chromosome complements of O. viridulus and Ch. brunneus agree in number, size range and centromere position. They differ however in size, those of O. viridulus especially the L-bivalents being longer. 2. This is paralleled by a marked difference in the mean and variance of the chiasma frequency and suggests that the increased chiasma frequency of viridulus may depend, at least in part, on structural change. 3. The differences between the two species depend upon changed chiasma properties in the three long and the three longest of the medium bivalents. In the L-bivalents the pattern is consistent, all three showing a significant increase in the mean value in O. viridulus. In the M-bivalents the pattern is inconsistent. The M4 of O. viridulus has a higher mean than that of Ch. brunneus with no difference in the variance while the M5 of O. viridulus shows an increased mean and variance over the M5 of Ch. brunneus. By contrast the M6 of O. viridulus has a lower mean and a lower variance than that of Ch. brunneus. 4. The increased chiasma values of O. viridulus are shared by the five longest bivalents (L1-M5 inclusive).
Meiosis in monosomic substitutions (20''W+1'W+1'R) was studied. Occasionally 4 univalents were observed. The rye univalent divided more often than the wheat univalent at anaphase I, as a result of which the rye chromosome lagged more frequently at anaphase II. Telocentric chromosomes and isochromosomes were transmitted more frequently in male gametes than in the female gametes. Chromosome mosaics were also observed.
The process of spindle fiber formation in pollen mother cells of Trillium kamtschaticum, was studied by electron microscopy. Initially, the spindle fibers appear as a mass of microtubules (about 25mμ in diameter) in the diakinetic cell (Figs. 10-12). This mass in the pollen mother cells seems to be restricted to the regions which correspond to the polar regions in later stages. The mass of microtubules enlarges during diakinesis. Later, after the fragmentation of nuclear envelope, the microtubules in the mass strech to the chromosomes in the nuclear area with tubular ER. Some of microtubules seem to connect with the kinetochor of each chromosome and form chromosomal fibers. The possibility of the mixing nuclear materials with cytoplasmic ones is discussed.
The present study analyzed quantitative relationship between the sex chromatin-like body (scl-body), the non-specific chromatins, and mitotic rate in the dermal cells of 10-, 15-, 20-, and 30-day old regenerating feathers of mature White Leghorn male and female chickens. The analysis showed that: 1. In both sexes the frequency of the scl-body is inversely related to the age of the regenerating feather. Its frequency in the female is three times that of its frequency in the male. The incidence of the non-specific chromatins, which are smaller in size than the scl-body, initially is higher in the male. As feathers develop, two sexes approach equality in this respect. Both types of chromatins can be observed only in the interphase nucleus. 2. A positive association exists between mitotic activity and the frequency of the scl-body. 3. The sex chromatin-like body in the chicken and the mammalian sexchromatin are not homologous structures.
Detailed analyses of chromosomes at pachytene and later stages of meiosis were made in a cultivated type of cassava. Pachytene chromosomes are depicted on the basis of total length, relative length, arm ratio, amount and distribution of heterochromatin and number and position of chromomeres. Idiograms showing details of all the eighteen pachytene bivalents in the haploid complement are presented and based on the average values of lengths obtained by accurate measurements of the bivalents in a minimum of 15 completely analyzable nuclei, the eighteen pachytene bivalents have been arranged and numbered in order of their decreasing length as chromosome I to chromosome XVIII. The haploid chromosomal complement, inter alia, has three functional nucleolar chromosomes and six chromosomal types represented in duplicate. Based on the data of the pachytene karyology obtained, a segmental allopolyploid origin of the present day cultivars of cassava has been suggested. Based on cytological data, it has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied.
PMC cytokinesis in Laurelia novae-zelandiae is of a type apparently unique in the literature. Remnants of telophase I spindle fibres persist in reduced form during meiosis II and near the end of this division two phragmoplasts, linking ‘cousin’ nuclei, are formed in the region of the telophase I spindle fibres. It is not clear whether or not these secondary spindle fibres are the result of intensification and extension of the telophase I spindle remnants. Cytokinesis occurs by cell plate formation and the heterotypic cell plate is completed shortly before the homeotypic ones have completed their centrifugal growth. Variants of the two apparent basic types of cytokinesis are summarized and the question as to which is the more primitive in angiosperms is discussed.