Diffuse Centromeres Research Articles

On the chromosomes of the geometrid moth genus Cidaria

1. The oogenesis of 44 (48) species of the Geometrid moth genus Cidaria has been studied. Spermatogenesis has been studied in two species only. 2. The most common (haploid) number among the Cidaria species so far investigated is 30, which is likewise the number second in commonness among the Lepidoptera as a whole. Most (33, or 75 percent) of the species have a chromosome number between 29 and 32, like most of the other groups of Lepidoptera. 3. No species has more than 32 chromosomes, whereas eleven have less than 29. The smaller chromosome numbers found are 28, 27, 25, 20, 19, 17, 13 and 12. 4. The great differences in chromosome numbers between closely related species are of interest. Such discrepancies are found in the subgenera Thera (variata and obeliscata 13, firmata 19, cognata 20 and juniperata 30), Lampropteryx (minna 17 and suffumata 32), and Hydrelia (testaceata 13 and flammeolaria 30). 5. The chromosomes are clearly bigger in the species with a low chromosome number than in those with a high one. In the chromosome sets of most Cidaria species studied the chromosomes are approximately equal in size. 6. Photometric measurements revealed that the DNA-content of closely related species is almost equal, in spite of great differences in chromosome numbers. This is also true of the subgenera investigated. This indicates that one chromosome in a species with a low number of chromosomes corresponds to two or more chromosomes of another one with a high chromosome number. 7. The discrepancies in the chromosome numbers among Lepidoptera have not arisen from polyploidy or differences in the degree of polyteny. They are due to “fragmentations” or “fusions”, which are rendered easier by the diffuse kinetochore. 8. It is obvious that in animals with a diffuse kinetochore some mechanism, possibly the location of sex-determining genes, reduces the role of chromosomal rearrangements in chromosomal evolution from what the diffuse kinetochore otherwise would allow. 9. Contrary to earlier assumptions of the author, chiasmata are not formed in the bivalents during oogenesis in the Lepidoptera. This is especially evident in preparations stained with Feulgen, when the elimination chromatin contained by the bivalents in the female remains unstained.

A New Subgenus in Luzula (Juncaceae)

The name Luzula purpurea is well known to those familiar with the literature of cytogeneties. Since the discovery that this species has relatively large chromosomes with diffuse centromeres, it has been the subject of much cytological study. Unfortunately, however, the name L. purpurea has no valid standing under the International Code of Botanical Nomenclature. The specific epithet was originally published, without a description, as JunUow purpureus by Buch (1816). Link, in a publication by Buch (1825) transferred this epithet to Luzula, but again without description. In both of the above citations, the name was attributed to Masson, but patient search has failed to turn up any publication by this worker in which Luzula (or Juncus) p?trpurea was described. The first time the name L. purpurea was published with a description was by Meyer (1849), who attributed the name to Buch and listed "Juncts purpureus Masson mser." as a synonym. The publication of the binomial L. piurptrea by Meyer is, however, antedated by L. elegans Lowe (1838), which is unquestionably the same species. Two other names have been applied to this species. The first, L. berthelotii Nees ex Kunth (1841), is clearly a synonym of L. elegans and the second, L. gracilis, is an herbarium name published by Trimen (1872) in a discussion of the distribution of L. purpurea (L. elegans). The nomenclature of this species has been complicated not only by the nomina nuda that have been applied to it, but also by confusion with another species. As pointed out above, the name Luzula purpurea has been in general use for this species up to the present time. It was taken up by Buchenau (1906) in his comprehensive monograph of the Juneaceae. In this same monograph L. elegans Lowe was listed as a synonym of L. purpurea, and a previously unvalidated herbarium name, "Luzula elegans Guthnick in Sched. hb. azor. Hochsffitetteri (1838) n. 126" was taken up for species currently known as L. purpureosplendens Seubert (1844). It is clear that the name L. elegans Guthnick cannot replace L. elegans' Lowe, as Buchenau evidently intended; Guthnick's name was not published until 1843 (Seubert & Hochstetter 1843), and then as a nomen nudumni. The species Luzula elegans Lowe, up to the present time, has beeni considered a member of the subgenus AntlJielaea. Although it resembles this subgenus superficially, it differs in three major morphological characters that were noticed by Buchenau (1906). First, the main infloreseence axis is actually a pseudorachis, formed by an overtopping of the main rachis by one of the major branches of the inflorescence. At each successive level this "rachis" is again overtopped by another major branch. This can easily be verified by observing the position of the brachts that subtend the major branches and the pedicels of the infloreseence (Fig. 1). In L. elegans each bract surrounds the base of an internode of the upright "rachis" (pseudorachis), indicating that this main axis is actually formed from a series of major infloreseence branches that successively overtop and crowd aside the morphologically terminal rachis. In all other species of

Gametogenesis in the Sugarcane Borer Moth, Diatraea saccharalis (F.) (Crambidae)

Diatraea saccharalis (F.), the only cytologically checked crambid moth up to the present, has an unusually low chromosome number for a lepidopteran, n = 17. The chromosomes apparently have a diffuse centromere. The premeiotic development of the gonads becomes more distinct after the fifth larval day, when the secondary gonia appear. The oogenesis proceeds very slowly after the formation of oocytes. A rapid deposition of yolk starts at the end of the pupal stage, and continues in the adult. The eggs flatten before they leave the body of the female. Meiotic metaphases can be encountered in the flat ovarial eggs. Six successive generations of spermatogonia are formed. Meiosis starts in the basal end of the testis follicles, opposite Verson's cell. From the fifth day on the larvae contain all stages of spermatogenesis, from the gonia to the spermiohistogenesis. A normal meiosis occurs during this period. The meiosis is abortive in the male pupa, because of asynapsis and anaphase irregularities. Bundles of spermatozoa appear as result of the spermiohistogenesis. The divisions are completed in the adult male. The testes are partly drained, but contain spermatids in spermiohistogenesis, and spermatozoon bundles.

The mode of meiosis in the Psyllina

1. The spermatogenesis of six psyllids and the oogenesis of Psylla forsteri have been studied. The haploid number n=13 was found in 4 species, all with an XO system of sex determination. 13 may well be the modal haploid number in the genus Psylla. 2. The chromosome complement of the only XY species, Psylla corcontum, with n=11, is probably the result of two chromosomal rearrangements which have led to the formation of a neo-XY pair. 3. Psylla forsteri is an XO species in which the haploid set consists of only 8 chromosomes, one of which is very large. As the amount of DNA in this species is approximately equal to that in the 13-chromosome species P. sorbi, the large chromosome obviously corresponds to 5 or 6 chromosomes of P. sorbi. 4. A diffuse stage, which leads to a considerable increase of nuclear size, is typical of late pachytene to late diplotene of spermatogenesis. 5. In contrast to the other cytologically studied Homoptera Sternorrhyncha, the bivalents of psyllids co-orientate at the first metaphase of spermatogenesis. The following anaphase is therefore prereductional. 6. In the oogenesis of Psylla forsteri the bivalents always seem to have auto-orientation, which means morphological postreduction at first anaphase. 7. The karyological picture is that of an organism with a diffuse kinetochore. 8. The Hemiptera and the plant genus Luzula both have diffuse kinetochores. The reason that the chromosome numbers in Hemiptera vary far less than in the genus Luzula may lie in the existence in the Hemiptera of a delicate system of sex determination sensitive to any change in chromosome number and structure. 9. Cytologically, the Psyllina lie between the suborders Sternorrhyncha and Auchenorrhyncha.

CYTOTAXONOMY OF CAREX SECTION CAPILLARES

The small section Capillares of the genus Carex has been studied from the cytological and taxonomical points of view. It comprises nine distinct species, one of which (C. Boecheriana) is raised to specific status in this paper. Three species include two distinct subspecies each; two varieties and three formae are accepted for two species respectively. The chromosome numbers of the taxa involved are 2n = 18, 36, 38, 40, 54, 56, and 58. It is pointed out that the chromosomes of Carex have a polycentric or diffuse kinetochore and that this explains the aneuploid variations in number known to be typical of the genus. Karyotypic analysis of the chromosome complements of the section Capillares revealed that in the basic diploid set of 2n = 18 chromosomes four units are long, 10 are medium and about half the length of the long ones, while four are small and about half the length of the medium ones. This frequency of size classes is also met with in the plants with 2n = 36 and 54 chromosomes. Those taxa with 2n = 38, 40, 56, and 58 chromosomes show, however, such a deviation in the frequency of the size classes that it seems logical that these numbers have been produced by a secondary fragmentation of the chromosomes. On the basis of karyotypic analysis of this section and other groups of the genus it is concluded that the primary basic number for the genus Carex in particular and the family Cyperaceae in general must have been x = 5, all other numbers having been derived mainly by fragmentation of chromosomes with a polycentric or diffuse kinetochore. This phenomenon of partial agmatoploidy is widespread in Cyperaceae, whereas complete agmatoploidy is typical of the closely related Juncaceae.

Post-Reductional Meiosis: Its Mechanism and Causes

ADDENDUMThe present paper was in proof when two other examples of diffuse centromeres or polycentric chromosomes were reported in the very recent literature, again in the class of Insecta (orders of Anoplura and Mallophaga).K. Bayreuther [1955, « Holokinetische Chromosomen bei Haematopinus suis (Anoplura, Haematopinldae »), Chromosoma 7: 260–270, 1955] observed the diffuse centromere during an investigation of the spermatogenesis of Haematopinus suis, n = 5, (class Insecta, order Anoplura). By X-rays treatment Bayreutheb obtained proof that the regular mitotic cycle takes place for chromosome fragments induced by the irradiation. Meiosis probably follows the post-reductional scheme, however the lack of any heteromorphous bivalent and the uniform tetrapartite structure of all five bivalents preclude certainty regarding the actual occurrence of post-reduction.A type of spermatogenesis very similar to that of Haematopinus has been reported by H. Scholl (1955, « Ein Beitrag zur kenntnis der Spermatogenese der...

POSTREDUCTION OF THE X-CHROMOSOME AND COMPLETE CHIASMA INTERFERENCE IN THE LAMPYRIDAE (COLEOPTERA)

Five species representing four genera in three of the five tribes comprising the Lampyridae of North America, the only genera known cytologically, have nine pairs of autosomes and an XX (♂): XO (♀) sex-determining mechanism. A single individual of one species, Pyractomena angulata, carried supernumerary chromosomes, which varied in number in different cells from zero to four. The X-chromosome of males is strongly, positively heteropycnotic during early prophase; the X-bivalent of females is indistinguishable from the autosomal bivalents at pachytene. The complements of the five species are indistinguishable but within the complement there are considerable differences both in size and in the position of the centromeres. In all five species the chiasma frequency per cell is without exception nine: univalents not being encountered, the recombination index for the family, as known cytologically, stands uniformly at 81. Chiasma interference, being complete, must therefore extend across the centromere. The supernumeraries, which approximate one-half the size of the smallest regular autosome, have a chiasma frequency of ca. 0.25 per chromosome, or one-half that of the smallest autosome. They thus demonstrate that, contrary to the evidence provided by the regular complement, a length-frequency relationship exists among the latter but is masked by the totality of chiasma interference. As in other beetles, the centromeres are localized, but the lampyrids are unique in having postreductional division of the X in males. Other insect groups with postreduction have, or are reputed to have, diffuse centromeres: one, the Odonata, is invariably postreductional.

Diffuse centromere, and other cytological observations on two desmids.

CYTOLOGICAL studies of the Desmidiaceae now in progress in this department have shown that the chromosomes of Cosmarium botrytis and Pleurotœnium kallis have a polycentric or diffuse centromere type of organization, which results in the parallel separation of the chromatids at anaphase (Fig. 1). This type of organization has been previously described in Spirogyra1, and among the higher plants in Luzula2 and Carex3.

ATYPICAL CHROMOSOME MOVEMENT IN MEIOTIC ANAPHASE OF BROMUS PITENSIS X B. MARGINATUS

THE CENTROMERE may be described as a specialized region of the chromosome, generally known to be structurally distinct, whose function is related to the movement of the chromosome during cell division. Three types of have been described. The most prevalent is the localized centromere, a single morphologically distinct structure occurring in a definite location in each chromosome. A chromosome with a multiple centromere, as found in germ-line cells of Ascaris megalocephala, contains numerous individually distinct centromeres which function in unison. In the Hemiptera and in Luzula and Tityus a diffuse centromere is apparently spread over the entire poleward-facing surface of the chromosome; its structure is not known.

Observações citológicas em Dysdercus cadeias de cromossômios em tecido somático de Dysdercus mendesi Bloete (Hemiptera-Pyrrhocoridae)

The male of Dysdercus mendesi Bloete (1937) has 2n = 16 chromosomes : 14 autosomes and 2 sex-chromosomes. Details are presented on the morphology of these chromosomes of the somatic cells of embryonic tissue. The long pair of rod shaped chromosomes is the longest of the set, and they show a conspicuous sub-terminal constriction (supposed to be the centromere) and five other smaller constrictions. In most of the other chromosomes sub-terminally localized constriction (supposed also to be the centromere) can also be observed. Based on these observations it has been concluded that the chromosomes of D. mendesi are morphologically normal. Dicentric chromosomes in the somatic tissue of this species are absent and the hypothesis of existence of diffuse centromere is also excluded. All of the chromosomes appear to have a definitive localized centromere. Metaphase spermatogonial plates have been observed where all the chromosomes appear as short and thick rods, apparently attached end-to-end, by definite connections, and forming a ring-shaped chain. Sometimes one or two chromosomes were found inside a ring formed by the others, but always connected to one or two of the chromosomes of the ring. Chromosomes chains of varied shapes were also found in the metaphase plates. In anaphase the longitudinally split chromosomes of the rings attain a curved shape as they move to the poles, giving the impression that both their extremities are pulled to the poles. A new hypothesis is presented to explain why the normal chromosomes of D. mendesi, provided with one localized centromere, can attain the curved shape observed in the anaphase configurations. It is based on the existence of connections attaching the chromosomes by their extremities, from metaphase until anaphase, and giving origin to the chain configuration already mentioned. These chains of chromosomes behave in anaphase as one rather long chromosomes with several centromeres. The centromeres are pulled to the poles, but as the extremities of the chromosomes of the chain are attached to each other, they give the false impression that both extremities of the chromosomes are being pulled to the poles, as if the chromosomes were provided with two centromeres, or as if there were diffuse centromeres.

A PRIMITIVE COCCID CHROMOSOME CYCLE IN PUTO SP

A primitive chromosomal cycle possibly archetypal for coccids is reported for Puto sp. of the family Pseudococcidae. There is no hermaphroditism nor any cytological evidence for parthenogenesis. The diploid chromosome number is 14 in the female, 13 in the male. Somatic mitosis is of the type characteristic for chromosomes with diffuse kinetochore. Meiosis is regular in both sexes. In the male it can be demonstrated to adhere to the coccid-aphid type, with: (a) the first division equational for non-crossover regions; (b) separation of chromatids and their secondary pairing during interkinesis, and (c) segregation of non-crossover regions in the second division. An XX -female, XO -male sex determining mechanism is present. Quadrinucleate spermatids are formed. This is the only coccid thus far reported with a simple and orthodox meiosis in both sexes.