Cerithium adustum and Cerithium nodulosum collected from the rocky shore on the Red Sea were karyotyped. These two species showed a distinct differentiation in the diploid chromosome number (2n=18 and 16 respectively). The karyotype of Certhium adustum consists of: six metacentric pairs and three submetacentric pairs while the karyotype of C. nodulosum consists of: two metacentric pairs, three submetacentric pairs and three telocentric pairs. Shell measurements of these species are also described in details in this paper. These results are reported for the first time in Egypt.
Three Argentinian oat lines (P1, P2 and RIL) and three synthetic hybrids among them were analized in the present communication. P1 and RIL differ for one reciprocal translocation. P1 and P2 presented two independent interchanges. For the first time meiotic irregularities during ecuational division in hexaploid oat hybrids are reported. This latter observation throw doubts on the dependence of anaphase onset on metaphase plate completition in oats.
A transplantable mouse model, each cell of which has a marker chromosome (Bj chromosome) was used in this experiment to determine whether maternal cells can migrate transplacentally to enter fetal circulation, the cell transplacental permeability at different embryonic development stages and a possibility of direct leukemia infection from mother to son (daughter). Our results indicate that during pregnancy the cell permeability of placenta depends on the embryonic development stage, e.g., very high cell permeability (100%) in an early- and mid-gestations of pregnancy and extremely low (4.5%) in the later stage. We also report here that maternal leukemia cells can transfer into the fetus transplacetally during pregnancy, leading to a direct infection of leukemia from mother to her offspring. Both the early- and mid-term gestations are more dangerous periods for the maternal leukemia cell infection.
The five species analyzed presented the same diploid number, 2n=48 chromosomes, but differed in karyotype formula. These results agree with the proposition that cichlids present a more conservative karyotype evolution and that the most frequent rearrangements appear to have been pericentric inversions and/or deletions. Only Crenicichla lepidota presented a multiple NOR system, indicating that the condition of a single nucleolar organizer is more primitive in this group. We may also state that constitutive heterochromatin seems to be highly conservative, with a preferentially pericentromeric pattern and with C-band positive NORs.
Chromosomal analysis of the three Egyptian species of the family Gekkonidae (Hemidac-tylus turcicus, Ptychodactylus hasselquisti and Tarentola annularis) have been studied. The diploid chromosome number of the three species is 2n=44, 2n=40 and 2n=42 respectively. All the chromosomes of the former species are acrocentrics while the latter two species have acrocentrics and microchromosomes. No differences were observed in the sex chromosomes of both sexes. Comparison of the karyotypic data of these species had been discussed.
Meiotic configuration of a cultivated rye with B chromosomes from China was characterized. Plants with two B chromosomes formed the highest frequency of a bivalent of B chromosomes while the multivalent formation of B chromosomes in plants with four B chromosomes was relatively high. The existence of B chromosomes had negligible effect on the mean chiasma frequency of A chromosomes. Spontaneous reciprocal translocations of A chromosomes were also detected in two out of 40 plants examined with the length of chromosome segment involved in translocations assumed to be different in the two translocation heterozygotes.
C. taxon (2n=32) was found to be unique in its cytological and morphological features; its karyotype consisted of two distinct genomes. However, karyological studies of C. gigantea (2n=12) revealed a remarkable karyomorphology as the 12 distinctly large somatic chromosomes of this species resembled the 12 large chromosomes of C. taxon (2n=32) in dimensions and karyomorphology. The ability of C. taxon (2n=32) and C. gigantea (2n=12) to hybridize and produce F1 hybrids demonstrates a closer relationship between these two taxa. The hybrids were studied with respect to the morphological characters, karyotype and chromosome association at meiosis. Most of the PMCs of the F1 hybrids show regular pairing among the large chromosomes of both parents, resulting in the formation of six larger bivalents and therefore it is evident that the 12 large chromosomes of both taxa are genetically homologous. Phenotypically the F1 hybrids resembled more closely to the female parent, C. taxon (2n=32), in plant height, size and shape of leaves, size of involucre etc. It has been assumed from the unambiguous cytological evidence that C. gigantea (2n=12) has participated in the origin of C. taxon (2n=32). It is suggested that C. taxon (2n=32) is probably an amphidiploid, arisen by natural hybridization between C. gigantea (2n=12) and C. lacryma-jobi (2n=20) and subsequent doubling of the chromosomes.
Cytomixis, representing the migration of chromatic material from one cell to another, was observed in PMC's of Polygonum tomentosum Schrank. Cytomixis was observed at all stages of meiosis, but became less frequent in the later stages of meiosis. Direct nuclear fusion and cytoplasmic connections between cells were noted, so that a series of PMC's were sometimes connected togther. Cytomictic cells were often accompined by other meiotic aberrations such as univalents, laggard and disoriented chromosomes. Levels of pollen stainability are low, indicating a high of male sterility in these populations.
A new functional type of chromosome in eukaryotes is described, involved in the orientation, driving or leading of the remaining chromosomes from the equatorial plate towards the poles of a dividing cell. This is the leader chromosome or forwarded chromosome, one for each haploid chromosomal set of the cell. This type of chromosome was identified long ago, both, in normal and mutagenic conditions. Untill now, no explanation for its existence has been proposed. When these chromosomes reach the poles of a dividing cell, they themselves constitute a milestone, as “the first beginning” for the organization of a superchromosomal structure in which every chromosome, belonging to a haploid set (nonhomologous chromosomes) enters in an ordered fashion by attaching through its telomere to a previous one. This results in a huge ring of nonhomologous chromosomes. This is a proper arrangement of interphase chromosomes which is a “sine qua non” condition for an ordered function of the genes and for a correct replication of the genetic material in eukaryotes. We have baptized this chromosome-which itself constitutes a milestone or marker for initiation of superchromosomal structure building-the Genome-Organizing-Chromosome (GOC).
Cytogenetic studies were conducted in Astyanax scabripinnis (Pisces, Characidae, Tetragonopterinae) species complex, from the Canta Galo brook (Tietê River basin, State of São Paulo, Brazil). Two sympatric cytotypes differing in diploid number and karyotype structure were detected. Almost all specimens presented 2n=50, with a karyotype consisting of 4M+26SM+4ST+16A and a fundamental number FN=84. However, two specimens in this sample-a female and a male-collected syntopically with that cytotype were found to be 2n=48 (6M+22SM+8ST+12A) and to have the same number of chromosome arms (FN=84). The two cytotypes showed some differences in constitutive heterochromatin distribution. The probable events implicated in this divergence and their significance are discussed, together with aspects of the evolutionary process of this species complex.
Distribution patterns of microtubules (MTs) in metaphase and anaphase spindles in Spirogyra were examined by electron microscopy. At metaphase, 9 to 12 MTs were attached to each kinetochore. Polar MTs terminated near the chromosomes at one end and never extended into the other half-spindle. At anaphase, polar MTs overlapped in the mid zone between the separating two chromosome-groups. The polar separation is interpreted as being powered by a driving force generated by the sliding of MTs at overlapping regions. Calculation of the number of MTs at several sites in the mitotic spindles yielded results consistent with this interpretation. The distribution patterns of MTs in the half-spindles remained almost unchanged during the polar separation, consistent with the fact that the size and shape of the half-spindle during anaphase also remained almost unchanged.
The mitotic and meiotic sex chromosomes of Belostoma oxyurum have been analyzed by C-banding and Ag-NOR staining. In mitotic prometaphases the Y chromosome and both telomeric regions of the X are C positive. However, at meiosis one telomeric region of the X chromosome presents always a C positive band, while the other telomeric region of this chromosome and the whole of the Y chromosome are light C banded during diplotene, the diffuse stage and early diakinesis. All these bands appear C positive by late diakinesis. In mitotic prometaphases, a positive Ag-NOR is revealed at one telomeric region of the X chromosome, but not in the Y chromosome. Besides, some intra and/or interindividual variation in NOR expression in the X chromosome is encountered. No positive Ag-NOR band is observed at meiosis. A comparison of the results obtained in mitotic and meiotic cells after C- and Ag-NOR banding lead to the conclusion that in Belostoma oxyurum the intermediate staining of the C-bands of the sex chromosomes at meiosis is related to both the DNA composition (repetitive DNA, rRNA genes) and its packaging (cycle of condensation).
In order to determine the influence of soil acidity on the meiotic behavior of maize microsporocytes, materials not selected for low pH soils consisting of inbred lines, single and double-cross hybrids were cultivated on acid and corrected soils in the Brazilian Central Plateau and in the Southern Region of the country. Cytologic analysis revealed the occurrence of countless chromosome abnormalities, among them figures closely resembling a phenomenon previously described in the literature that affects both mitosis and meiosis. This abnormality is characterized by intense chromosome fragmentation. The phenomenon was spontaneous its phenotypic expression was very intense and its incidence was higher in inbred lines cultivated on acid soil. Possible effects of genotypic and environmental factors are suggested as the origin of this phenomenon.
Cytologic heterogeneity of triticale (Triticosecale Wittmack) has been well studied at both varietal and intravarietal levels. The aim of this work was to determine the degree of association between meiotic index (MI) or percentage of normal tetrades and post-tetrades index (PTI), namely percentage of abnormal microspores. Eight hexaploid triticale sublines from two different varieties, Don Frank (DF) and Jenkins TA 203 (J) were evaluated during two years. Statistical analysis showed a dissociation between indexes in J variety. PTI index would be most suitable for intravarietal selection based on cytological aspects.
The causes of partial male sterility were studied in an inbred maize line. Meiotic analysis revealed a high frequency of countless irregularities. Particularly outstanding among them were univalent chromosomes, irregular segregation at meiosis I and II, micronuclei, chromosome breaks and bridges, sticky chromosomes, absent or defective cytokinesis, cell fusion, chromatin degeneration and pycnosis, abnormal spindles, giant cells, numerical chromosome variations, dyads, triads, polyads, multinucleate microspores and pollen grains of varying size. Although the frequency of irregularities was high, not all microsporocytes were affected. The present results are compared to literature data about genetic male sterility.