Showing papers in "Chromosoma in 1969"

Patterns of puffing activity in the salivary gland chromosomes of Drosophila. IV. Variability of puffing patterns.

Abstract: Patterns of puffing activity during the third larval instar and the prepupal period of two different strains of D. melanogaster (Oregon and vg6) are compared. The variation in puffing activity observed is both quantitative (involving the mean size or timing of activity of individual puffs) and qualitative. The pattern of activity of 64% of the puffs is the same in the two strains, 12% show strain differences in puff size and 19% in the time of their activity. One puff (64C) is active only in one of the strains (vg6). In genetic experiments this puff segregates normally and the puff locus has been mapped genetically to a site coincident with, or at least very close to, the cytogenetic position of the puff. In heterozygotes the puff is homozygous only when the maternal and paternal homologues are synapsed. When the homologues are asynapsed only the homologue from the vg6 parent is puffed at 64C. With the exeption of some strains closely related to vg6 no other strain of D. melanogaster has been found to possess puffing activity at 64C. In vg6/In(3LR)C165 heterozygotes 64C forms a heterozygous puff even when the homologues are synapsed. In the discussion consideration is given to the various factors that control puff size.

The fine structure of meiotic chromosome polarization and pairing in Locusta migratoria spermatocytes

Abstract: At the leptotene stage of meiotic prophase in Locusta spermatocytes (2n=22 telocentric autosomes + X-chromosome), each chromosome forms an axial core. The 44 ends of the autosomal cores are all attached to the nuclear membrane in a small region opposite the two pairs of centrioles of the juxtanuclear mitochondrial mass. At later stages of meiotic prophase, the cores of homologous chromosomes synapse into synaptinemal complexes. Synapsis is initiated near the nuclear membrane, in the centromeric and the non-centromeric ends of the chromosomes. Homologous cores have their attachment points close together and some cores are co-aligned prior to synapsis. At subsequent stages of zygotene, the number of synaptinemal complexes at the membrane increases, while the number of unpaired axial cores diminishes. At pachytene, all 11 bivalents are attached to the membrane at both ends, so that there are 22 synaptinemal complexes at the membrane near the centrioles. Because each bivalent makes a complete loop, the configuration of the classic Bouquet stage is produced. The X-chromosome has a poorly defined single core at pachytene which also attaches to the nuclear membrane. These observations are based on consecutive serial sections (50 to 100) through the centriolar zone of the spermatocytes. Labeling experiments demonstrated that tritiated thymidine was incorporated in the chromatin of young spermatocytes prior to the formation of the axial cores at leptotene. It is concluded that premeiotic DNA synthesis is completed well in advance of pairing of homologous chromosomes, as marked by the formation of synaptinemal complexes.

A simple method for preparing meiotic chromosomes from mammalian testis.

Abstract: Freshly removed testis tubules are treated with hypotonic citrate solution and fixed in 3∶1 acetic alcohol without undue rupture. The material is transferred to 60% acetic acid and the resulting suspension is air-dried onto warm slides using a micropipette. Finally the slides are stained with lacto-acetic orcein. — Provided suitable storage is made, slides need not be prepared in the same week as fixation and this may facilitate the collection of material during field study.

Chromosomen-Aktivität und biochemische Zelldifferenzierung in den Speicheldrüsen von Camptochironomus

Abstract: Salivary glands of Camptochironomus tentans and C. pallidivittatus were used to study the question whether genes controlling the synthesis of characteristic cell proteins are located in chromomeres specifically puffed in this tissue. Salivary gland cells produce considerable amounts of secretory proteins. In G. tentans, this secretion was shown by gel electrophoresis to consist essentially of 5 protein subunits. In C. pallidivittatus, a component (no. 6) additional to these was found. Another constituent of the secretion (no. 7) is synthesized in C. pallidivittatus by only a small group of gland cells. — The inheritance of these species- and cellspecific proteins has been investigated by relating their presence in interspecific hybrids to the chromosome constitution. Fraction no. 6 was found to be correlated to a short distal region of chromosome IV in which a tissue-specific Balbiani ring is located. Secretion component no. 7 which is characteristic of the special gland lobe of C. pallidivittatus is also controlled by chromosome IV which in this lobe develops a cell-specific Balbiani ring.

Formation of spindle fibers, kinetochore orientation, and behavior of the nuclear envelope during mitosis in endosperm

Abstract: The formation of kinetochore (chromosomal) and continuous fibers, and the behavior of the nuclear envelope (NE) was described in studies combining light and electron microscopy. Microtubules (MTs) “push” and “pull” the NE which becomes progressively weaker before breaking. It breaks to a certain extent due to mechanical pressure. Clear zone MTs penetrate into the nuclear area as dense bundles and form continuous fibers. These MTs also attach to some kinetochores during this process. Some kinetochore fibers seem to be formed by the kinetochores themselves which are also responsible for further development and changes of kinetochore fibers. Formation of kinetochore fibers is asynchronous for different chromosomes and even for two sister kinetochores. Often temporary “faulty” connections between different kinetochores or the polar regions are formed which usually break in later stages. This results in movements of chromosomes toward the poles and across the spindle during prometaphase. The NE, whose fine structure has been described, breaks into small pieces which often persist to the next mitosis. Old pieces of NE are utilized in the formation of new NE at telophase. Several problems concerning the mechanism of chromosome movements, visibility of the NE, etc., have also been discussed.

End-to-end chromosome attachments in mitotic interphase and their possible significance to meiotic chromosome pairing

Abstract: Cytological studies on telophase and early prophase in roottip cells of several plant species (Allium cepa, 2n=16; four Crepis species, including Crepis capillaris, 2n=6; Callitriche hermaphroditica, 2n=6; Nigella arvensis, 2n=12; Secale cereale, 2n=14) revealed that chromosome ends are attached two by two forming chains of chromosomes (interphase associations). In these chains homologous chromosomes are presumably located adjacent to each other. In Crepis capillaris it was observed that the two nucleolar chromosomes form a separate ring one end attached to the ring of the four remaining chromosomes and the other end attached to the nucleolus. It is proposed that these end-to-end attachments have significance for chromosome pairing in meiosis. The adjacent location of homologous chromosomes in the interphase associations would facilitate rapid and regular synapsis.

Gene Amplification in the Oocytes of Dytiscid Water Beetles

Abstract: A conspicuous mass of extrachromosomal DNA (Giardina's body) is found in oogonia and oocytes of Dytiscid water beetles. Since in older oocytes this DNA is associated with numerous nucleoli, it seemed probable that the ovary might contain extra copies of the genes for ribosomal RNA (rRNA). This hypothesis has been confirmed by centrifugation and molecular hybridization studies. —In Dytiscus marginalis and Colymbetes fuscus a high density satellite DNA is found in somatic cells and in sperm. Hybridization experiments show that all of the rDNA, i.e., those sequences complementary to rRNA, are located in this satellite, although quantitatively they make up only a small fraction of the satellite. In both species the DNA isolated from ovariole tips is enriched with respect to the satellite. A parallel enrichment of the rDNA has been shown in ovariole tips of Colymbetes, but for technical reasons has not been examined in Dytiscus. —The following model is proposed. In somatic cells and sperm the rDNA is part of an extensive region of high density DNA in one or more chromosomes. In oogonia and oocytes the entire high density region is replicated extrachromosomally and appears cytologically as Giardina's body.

Mitotic instability leading to an accumulation of B-chromosomes in grasshoppers.

Abstract: The study of mitotically unstable B-chromosomes (supernumeraries) of two grasshopper species confirmed a suggestion made earlier (Nur, 1963) that the instability should always be associated with a tendency of the B's to increase in frequency. Among 780 Camnula pellucida (Scudder) males from California, 105 had B's. In the testes of these males the number of B's varied from follicle to follicle and ranged between 0 and 4. Because of this variation, the number with which each male started to develop could not be determined. However, the relatively low frequency of males with B's and the regular meiotic behavior of the latter suggested that most of the 105 males started with a single B. Cytological analysis of the cells of the gastric caeca of 31 males whose testes contained B's confirmed this suggestion by showing that only one male had two B's in these cells; all the rest had one. In the testes of the 74 other males the mean number of B's ranged from 0.89–2.50, but only two males had means higher than 2.00. The observed ratio of one male with two B's to 30 with one, suggested that only the two males with the highest means started to develop with two B's and that the other 72 males all started with one. Since the mean for the 72 males was 1.37 B's per male, it was concluded that during the development of the testes of these males the mean increased by 37%. The males with B's had fewer follicles in their testes and apparently had also a lower frequency of normal sperm. — The analysis of the testes of Locusta migratoria L. males from Japan gave results which agreed with those from C. pellucida.

Chromosome multiformity in the genus Ctenomys (Rodentia, Octodontidae). A progress report.

Abstract: The karotypes of eleven species of the South American burrowing rodents, genus Ctenomys are described, and information on the somatic number of two other species of the same genus is given. The studied species are: C. torquatus (2n ♂=68), C. tuconax (2n ♂=61), C. minutus (2n=50), C. talarum (2n= 48), C. porteousi (2n=48), C. cf. minutus (2n=48), C. australis (2n=46), C. azarae (2n=48), C. latro (2n=42), C. magellanicus fueguinus (2n=36), C. tucumanus (2n=28), C. opimus luteolus (2n=26), and C. occultus (2n ♀=22). This extreme intrageneric variation in somatic number is also reflected by a great amount of diversity in chromosome structure. Karyotypes seem to be rather constant at the species level. Autosomal polymorphism has been found in two of the species, namely C. talarum and C. latro. The hypothesis of the superimposition of Robertsoman rearrangements, pericentric inversions and translocations in the evolution of the karyotype of Ctenomys is advanced. The direction of chromosome change, either toward increase or decrease in chromosome number, is discussed. It is emphasized that high chromosome multiformity is correlated in Ctenomys with a rapid and explosive pattern of species diversification; the meaning of the small size of populations in enhancing the role of chromosome rearrangements in the evolution of Ctenomys is discussed.

Variation in the activity of nucleolar organizers and their ribosomal gene content.

Abstract: In metaphase preparations from leucocytes of the toad, Bufo marinus, conspicuous secondary constrictions are present in the number 7 pair of chromosomes. These constrictions were considered to be the nucleolar organizers since they were associated with nucleoli during prophase. In 35 out of 60 individuals taken from natural populations, the homologous nucleolar organizers produced two equal-sized nucleoli and secondary constrictions (Group I animals). Pour animals (Group II) had only one very large secondary constriction in the majority of their metaphase preparations and an abnormally high frequency of cells containing one nucleolus. The remaining 21 animals (Group III) had unequal-sized constrictions in most of their metaphases but were more variable than the individuals of Groups I or II since they also had metaphases with two equal constrictions or only one constriction. The DNA from individuals of each group was hybridized with radioactive ribosomal RNA in order to correlate the size of nucleoli and constrictions with the amount of DNA (rDNA) homologous to ribosomal RNA. The two animals of Group II which were studied contained 0.056% of their genome homologous to ribosomal RNA a value considerably higher than those found for any of the animals of Groups I or III. These high values for rDNA coupled with the morphological appearance of the nucleolar homologues suggested a duplication of the nucleolar organizer in the homologue with the long constriction. The amount of rDNA in animals of Group I and III varied between 0.025 and 0.048% of the genome. Although the animals with unequal-sized constrictions (Group III) had generally lower contents of rDNA than those with equal-sized constrictions (Group I), the values overlapped between the two groups. Further evidence which correlates the size of nucleoli with the number of ribosomal RNA genes comes from studies with a “small nucleolar” mutant of the Mexican axolotl (Ambystoma mexicanum). Animals homozygous for this deletion were found to contain only 55% of the complement of rDNA present in the wild type. It is concluded that partial deletions and duplications of the nucleolar organizer as well as highly variable contents of rDNA are common in the genome of these amphibians.

Microchromosomes in holocephalian, chondrostean and holostean fishes

Abstract: Chondrostean and holostean fish of today are leftover relics: they share some characteristics with the venturesome crossopterygian fish, which launched the evolution of terrestrial vertebrates about 280 million years ago. The chromosome complements and DNA values of one chondrostean and two holostean species as well as one holocephalian species were studied. Their DNA values varied from 37% to 50% of that of mammals, and three of the species contained dot-like microchromosomes in their diploid complements. Their genome size and karyological characteristics are quite similar to those possessed by one group of reptiles and by avian species.

Heterochromatin and chromosome aberrations

Abstract: The chromosome breaking effect of mitomycin C, methyl methanesulfonate, maleic hydrazide, 8-ethoxycaffeine and gamma rays on the primary root meristematic cells of Nigella damascena was studied. All the agents tested except 8-ethoxycaffeine, produced relatively fewer aberrations, when compared to Vicia faba cells, though both the species have nearly similar total chromosomal length. Test for the presence of heterochromatin in Nigella gave negative results and it is interpreted that the observed differences between Vicia and Nigella are due to the presence and absence of heterochromatin in their chromosome complements respectively. The role of heterochromatin in the production of chromosome aberrations and its significance in evolution are briefly discussed.

Synaptinemal complexes in the achiasmatic spermatogenesis of Bolbe nigra Giglio-Tos (Mantoidea)

Abstract: In chiasmatic meiosis of mosquitoes, ascomycetes and lilies the synaptinemal complex (SC) disassociates from the bivalent before metaphase I. Conversely, in the achiasmatic meiosis of Bolbe nigra, the SC remains associated with the bivalent during first metaphase. Light microscopy reveals mid-bodies between disjoining half-bivalents during early first anaphase in Bolbe. Optically controlled serial sections for electron microscopy show that the mid-bodies seen in light micrographs and synaptinemal complexes seen in electron micrographs are the same structure. Electron micrographs indicate that the SC breaks transversely at a point corresponding to the chromosomal kinetochore during anaphase I as the chromatin and the SC begin to separate. During telophase I, SC remnants are at the poles with the chromosomes or between poles. Presently, the evidence is inadequate to state whether the SC serves alternately or simultaneously as a biological contrivance for conjunction and crossing-over or singly as a device for one of these phenomena.

Patterns of puffing activity in the salivary gland chromosomes of Drosophila. II. The X-chromosome puffing patterns of D. melanogaster and D. simulans.

Abstract: Salivary gland X chromosome puffing patterns are described for the Oregon stock of Drosophila melanogaster and for the Berkeley stock of D. simulans. In D. melanogaster regular phase specific puffing was recorded at 21 loci in the third larval instar and subsequent prepupal stage. A comparison of the X chromosome puffing patterns of male and female larvae failed to show any qualitative differences although in the males a group of puffs were active for a longer time during development than in females. The X chromosome puffing patterns of D. simulans are similar to those described for D. melanogaster although two puffs (4F 1–4 and 7B 1–3) were active in D. simulans but not in D. melanogaster. The sex differences in puffing observed in D. melanogaster were also observed in D. simulans.

Induced and developmental variation in chromosomes of meristematic cells

Abstract: Change in chromosome size in root tip meristems of rye and Allium cepa are induced by growing the plants in solutions differing in phosphorus content. The chromosomes are 50% larger by volume in a “high” phosphate as compared with a “no” phosphate solution. Alteration of other elements supplied in culture also induces change in the size of chromosomes. — The size variation is a reflection of change in the chromosome dry mass. In part at least this change in mass is attributable to alteration in the amount of protein. The DNA component of the chromosomes remains unchanged. — A consistent pattern of change in chromosome size, quite independent of that induced by varying the culture solution, is related to age and development. For example, the root tip chromosomes double in size during the first three weeks of growth in rye seedlings. Thereafter the size decreases. As with the induced chromosome changes the protein content alters, the DNA amount remains constant. — Variation in the “non-permanent” component of the chromosomes in meristems appears to be closely correlated with the rate of cell metabolism.

Decreased DNA content of birch (Betula) chromosomes at high ploidy as determined by cytophotometry

Abstract: Relative amounts of DNA were determined on telophase nuclei by Feulgen cytophotometry for euploid taxa of birch (Betula) with somatic chromosome numbers of 28, 42, 56, 70, and 84. A direct correlation was found between observed DNA absorbance and chromosome number except for plants of B. papyrifera with 84 somatic chromosomes. The DNA density value for nuclei of the 84-chromosome plants fitted a 1∶2.25 ratio instead of the expected 1∶3.0 ratio. The DNA density value for these plants was calculated to be approximately equivalent to plants which would possess 63 somatic chromosomes. The average DNA value per chromosome was 2.73 for the 84-chromosome plants in contrast to 3.50 per chromosome in each of the lower euploids. Nuclear diameters of the 84-chromosome plants were directly related to chromosome number and not to DNA density value. The genomic number of Betula was considered to be x=7, rather than x=14, since a DNA value equivalent to 63 chromosomes is a multiple of 7 and not 14. Diploid birch species (2n=2x=28), therefore, would actually be tetraploids (2n=4x=28). The reduction in DNA content may be an adaptation for the establishment of higher ploidy in birches.

Multiple nucleoli and enhanced nucleolar activity in the nurse cells of the insect ovary

Abstract: Origin and function of the nucleolar apparatus in nurse cell nuclei of Calliphora erythrocephala have been investigated by cytological and autoradiographic methods in some inbred lines of laboratory blowflies with well paired polytene chromosomes in the nurse cell nuclei. Besides the nucleolus at chromosome VI large numbers of multiple free nucleoli develop in the highly polyploidized nurse cells during oocyte growth. The nucleoli incorporate H3-uridine in a considerable amount producing a homogeneous and RNase-sensitive label even after short time incubation. Their capacity of RNA synthesis is independent of their spatial relationships to other nuclear components. DNA particles in the nucleoli could be identified by the Feulgen reaction and by fluorescence staining with N,N'-diethylpseudoisocya-ninchloride, which also demonstrates the existence of own templates for autonomous RNA synthesis. There are indications that the nucleolus' own DNA is produced by gene amplification beyond the level of endomitotic polyploidization in the nurse cell nuclei. A quantitative estimation of grain density in the autoradiograms shows a rigorous shift of rRNA synthesis: at least 72% of all newly synthesized macromolecular RNA in nurse cell nuclei as contrasted to 13 % of nucleolar RNA synthesis in bristle forming cells with a similar degree of polyploidy. It seems that the nurse cell nuclei of Calliphora in addition to polyploidization increase their template capacity for synthesizing rRNA in a similar way as has repeatedly been demonstrated for Amphibia. Cytological and physiological peculiarities of the nurse cells have been discussed from the viewpoint of their functional similarity to the oocyte nucleus.

The inhibition of protein synthesis in meiotic cells and its effect on chromosome behavior.

Abstract: Autoradiographs show that tritiated leucine is incorporated into protein continually at an almost linear rate during meiotic prophase of lily microsporocytes in in vitro culture. Although label is mostly in the cytoplasm for the first hour, it becomes almost evenly distributed throughout the cell after a few hours. The amount of label decreases slightly, if at all, during a chase period extending through the rest of the prophase — a period of 3 to 4 days. — The incorporation of label was blocked by 95% by the protein inhibitor, cycloheximide, at a concentration of 3.5 × 10-6 M. In the presence of this inhibitor, meiosis was arrested at all stages through metaphase I and even later. After temporary inhibition, however, or in low drug concentrations, characteristic cytological abnormalities subsequently developed, depending on the meiotic stage at which the inhibition occurred. One important observation was that the formation of chiasmata between homologs could be blocked if the inhibition was applied during the late zygotene or early pachytene stages.

The diffuse diplotene stage of meiotic prophase in Neurospora.

Abstract: The prophase stages of meiosis in Neurospora crassa are re-examined following McClintock (1945) and Singleton (1953). A diffuse chromosome stage occurring between pachynema and diakinesis is described. It is proposed that the diffuse stage does not necessarily represent a condition of intense gene activity in the sense of directing the metabolic activity of the ascus.

Karyotypes of Malayan rats ( Rodentia-Muridae , genus Rattus Fischer)

Abstract: The karyotypes of 18 species of Malayan rats, genus Rattus Fischer, are reported. Present studies reveal that the karyotype of rats is not species-specific. The variability in diploid number (2n) within the genus Rattus is reaffirmed. A range of 36 to 52 is reported, with 2n=42 having the highest frequency. The affinity of Malayan rats is discussed on the basis of chromosomal evidence.

Parallel mosaicism of supernumerary chromosomes and sex chromosomes in Echymipera kalabu (Marsupialia).

Abstract: Echymipera kalabu (Peramelidae: Marsupialia) does not have the full chromosome complement in all its adult somatic tissues. The chromosomes missing are the Y-chromosome in the male and an X-chromosome in the female. The full complement is present in the corneal epithelium and the reproductive tissue. A parallel mosaicism to this exists with respect to small supernumerary chromosomes which are found in certain animals of this species. These supernumeraries must be subject to the same control system as that which is responsible for the elimination of the sex chromosomes.

Fine structural studies of apolar mitosis.

Abstract: A fine structural analysis of apolar mitosis induced by chloral hydrate was made on Haemanthus katherinae Bak. endosperm. Under the influence of chloral hydrate MTs disappear initially and then are formed de novo. Kinetochore fibers grow away from kinetochores and their formation is asynchronous for all chromosomes in the set and also for sister kinetochores. Bundles of MTs forming kinetochore fibers converge toward one of the poorly defined polar regions during formation of kinetochore fibers (metaphase) and in motionless kinetochores. Such MTs increasingly diverge when kinetochores move during anaphase. The relation of ER to formation of MTs is evident and briefly discussed. A continuous transition exists between NE and ER during formation and disintegration of the NE. Some theoretical aspects of these problems were also discussed.

A comparative study of the chromosomes of birds

Abstract: Karyotype analysis and morphometric measurement of the chromosomes of eleven species of Indian birds are described. The unequivocal identification of W chromosome in the females of five species of the present investigation further strengthens the generalisation that, at least in Carinatae, the sex chromosome constitutions are of ZZ and ZW types in males and females respectively. — The chromosomes of different species of birds so far worked out in each order have been compared using quantitative methods and tentative conclusions have been drawn regarding chromosomal affinities between species of different taxonomic categories.

On the sex chromosome trivalent in some Lepidoptera females

Abstract: In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The “broken” chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY1Y2 for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.

Chromosomal RNA synthesis in polytene chromosomes of Chironomus tentans.

Abstract: The presence of heterogeneous RNA of high molecular weight has been demonstrated on the giant chromosomes, in the nuclear sap and in the cytoplasm of the salivary glands in Chironomus tentans. The kinetic properties of this heterogeneous RNA have also been outlined in some detail. — Salivary glands were incubated for different time intervals (20, 45 and 180 min) in haemolymph, supplemented with tritiated cytidine and uridine. The different cellular components were isolated by micromanipulation and RNA extracted with an SDS-pronase solution and analysed with electrophoresis in agarose. — Heterogeneous, high molecular weight RNA with a peak around 35 S was saturated with label on chromosome I, II and III in 45 min, although the synthetic capacity was unchanged during at least 180 min incubation. This indicated a complete turnover of heterogeneous RNA on the chromosomes in less than 45 min. The turnover time in the giant puffs (the so called Balbiani rings) on the fourth chromosome, was even shorter and estimated to less than 30 min. No shift in the electrophoretic pattern of this heterogeneous RNA was found to occur on the chromosomes during long incubation times or during actinomycin D experiments. These labelling characteristics of heterogeneous RNA on the chromosomes indicate that all the different molecules in the heterogeneous RNA have a similar and rapid turnover. A conversion to smaller, stable molecules was excluded. — Heterogeneous RNA of a distribution corresponding to that on the chromosomes was found in the nuclear sap and also in the cytoplasm. The activity in both these cellular compartments increased between 45 and 180 min incubation. The distribution pattern for high molecular weight RNA was in all experiments similar on the chromosomes, in the nuclear sap and in the cytoplasm. It appears that at least a considerable part of the high molecular weight RNA leaves the chromosomes to enter the nuclear sap and lateron to some extent the cytoplasm in this high molecular form. Stable molecules of smaller size (6–15 S) did not appear during 180 min incubation. The data indicate, however, also a substantial breakdown of heterogeneous RNA to acid soluble products during this time.

Coordinated development in the foot pad of the fly Sarcophaga bullata during metamorphosis: changing puffing patterns of the giant cell chromosomes

Abstract: A description is given of the puffing sequences of the giant polytene chromosomes from the footpads of Sarcophaga bullata, from Day 3 to Day 12 of pupation at 25° C. The chromosome puffing patterns are seen to be very precise and to occur in orderly sequence with respect to general developmental events. Particular puffs appear or regress in a continuous, orderly sequence. A few puffs remain throughout adult development. Most are puffed for a limited time only. In several cases puffed regions appear to “move along” the chromosome, suggesting sequential activity of adjacent genetic loci. Attempts are made to correlate chromosome puffing with specific cellular activities — cell growth, the sequential secretion of six cuticular layers (determined by electron microscopy), cuticle sclerotization and melanization, and eventual cell death. Preliminary observation of thoracic trichogen cell chromosomes show interesting similarities and differences in puffing patterns, when compared with footpad sequences.

RNA synthesis in a Balbiani ring in Chironomus tentans salivary gland cells.

Abstract: Rapidly labelled RNA in Balbiani ring 2 on chromosome IV in the salivary glands of Chironomus tentans was investigated. This RNA is likely to be transcribed from only one chromosomal band, supposed to be a single operational unit in these polytenic cells (Beermann, 1966).

The origin of multiple oocyte nucleoli from accessory DNA bodies in Gryllus domesticus

Abstract: 1. Die interphasischen Oogonienkerne von Gryllus domesticus enthalten mehrere kleine, kugelformige DNS-Korper, die von Nukleolen umhullt sind (Abb. 3 und 4). Wahrend der Kernteilungen lockern sich die DNS-Korper in dunne Faden auf (Abb. 5 und 6) und werden in vielen Fallen unsichtbar. Diese Faden sind zusatzliche DNS-Elemente neben den 22 Metaphasechromosomen. Daher ist die Annahme, DNS Korper und X-Chromosomen seien miteinander identisch, hinfallig (vgl. dagegen Sotelo und Wettstein, 1964). In den alteren Oogonien vermindert sich die Anzahl der DNS-Korper zugunsten einer deutlichen Grosenzunahme der wenigen Korper, die ubrigbleiben. 2. Die Primaroocyten besitzen im Lepto- und Zygotanstadium meist nur noch einen einzigen, allerdings sehr viel groser gewordenen DNS-Korper. Dieser zerteilt sich im Pachy- und Diplotan vollstandig in einzelne Fasern, die sich schlieslich voneinander losen und im Kernraum ausbreiten (Abb. 10 und 11). Mit der Entspiralisierung des DNS-Korpers lauft eine Vermehrung der Nukleolen parallel, die an den DNS-Fasern entstehen und sich mit diesen gemeinsam uber weite Bereiche des Oocytenkerns verteilen (Abb. 11). Fruhere Untersuchungen (Kunz, 1967) hatten ergeben, das diese Nukleolen wie die multiplen Oocytennukleolen der Amphibien ringformig gestaltet sind. Die den Nukleolen zugrunde liegende DNS geht bei Gryllus auf den DNS-Korper der fruhen Stadien zuruck. 3. Auf autoradiographischem Wege wurde ein gegenuber den Chromosomen asynchroner Thymidineinbau im DNS-Korper der Oogonien und Oocyten festgestellt (Abb. 7). 4. Laterale Lampenburstenschleifen, die zuerst im Zygotan sichtbar werden, entstehen nicht nur in der weiblichen Meiose, sondern auch in den entsprechenden Prophasestadien der Mannchen (Abb. 8). 5. Ein auffallendes, positiv heteropyknotisches Chromozentrum ist auch in den Spermatogonien und meiotischen Prophasestadien der Mannchen enthalten (Abb. 8), ohne jedoch regelmasig mit dem Nukleolus verbunden zu sein (Abb. 9 und 14). Es handelt sich hierbei nicht um einen akzessorischen DNS-Korper wie in den weiblichen Keimzellen, sondern um das univalente X-Chromosom. 6. Diploide somatische Zellen enthalten nur zu einem geringen Prozentsatz zwei Nukleolen; in den meisten Fallen sind die beiden Nukleolen zu einem einzigen Gebilde verschmolzen. Im Vorkommen zweier Nukleolen liegt zwischen Mannchen und Weibchen kein signifikanter Unterschied vor. Das wird als Hinweis dafur gewertet, das der Nukleolenbildungsort auf einem Autosomenpaar liegt, nicht auf den (beim Weibchen doppelt, beim Mannchen nur in Einzahl vorhandenen) Geschlechtschromosomen. 7. In der Oogenese von Gryllus ist die Nukleolen-DNS in hohem Mase vervielfacht, wahrend die ubrigen Gene (in der G2-Phase) nur in vierfachem Satz vorliegen. Der Grund fur die selektive Multiplikation der Gene des Nukleolenbildungsortes liegt wahrscheinlich darin, das in der Oogenese die gesamte ribosomale RNS fur einen vielzelligen Embryo aufgebaut werden mus, andererseits aber in der Keimbahn keine endo-mitotische DNS-Vermehrung moglich ist.

Inversion heterozygosity and sub-chromatid exchange in Agave stricta

Abstract: A plant of Agave strictaSalm. (2n=60) has a bimodal complement of 10 L, 4 M and 46 S chromosomes. It is heterozygous for a paracentric inversion which involves the middle third of the long arm of one of the L chromosomes. It produces at anaphase I bridges and fragments and also loops and fragments, both single and double. Breakage and reunion at the sub-chromatid and at the chromatid level produce side-arm bridges and bridges and fragments respectively at anaphase I. A method is given, based on chiasma frequency, which will in certain cases of inversion heterozygosity provide a reasonable estimate of the position and the length in genetic map units of an inverted segment with respect to the whole chromatid arm.

Stable telocentric chromosomes produced following centric misdivision in Myrmeleotettix maculatus (Thunb.)

Abstract: The standard complement of Myrmeleotettix maculatus includes a pair of L3 metacentric chromosomes but throughout the germ line of a structurally mutant male individual one of these had been replaced by two telocentrics These chromosomes divided normally at mitosis and at meiosis paired completely with the arms of the remaining L3 There was no tendency for the two terminal centromeres to fuse At first anaphase the two rods usually segregated from the metacentric which resulted in the formation of a high percentage of balanced gametes On the basis of this evidence and the morphological appearance of the centric region it has been concluded that the derived telocentrics evolved following misdivision through the inner zone of the metacentric centromere In view of their apparent stability it has been proposed that, contrary to certain beliefs, centric fission may have played an important role during karyotype evolution in the Acrididae