Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The chromosome complement of Gueriniella serratulae (F.) Fernald, Tribe Iceryini, Subfamily Monophlebinae of the primitive coccid Family Margarodidae, is 2 n ♀=6; males are unknown. Reproduction is by thelytokous parthenogenesis. Meiosis is normal; polar bodies do not contribute to the formation of a zygote-substitute nucleus; and development is initiated by a haploid cleavage of the female pronucleus. Diploidy is restored by the fusion of the 2 nuclei resulting from this division. With the exception of Gueriniella, all cytologically known Iceryini are haplo-diploids, with a chromosome complement of n=2. The hypothesis is proposed that Gueriniella is a persistent primitive stemming from the ancestral iceryine stock prior to the loss of the sex chromosomes and the evolution of haplo-diploidy within the tribe. A review of the available evidence from cytology, taxonomy, endosymbiosis, behavior and distribution shows good agreement with this interpretation.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In the Panamanian iceryine coccid Icerya zeteki Cockerell (Family Margarodidae Morrison) all females become hermaphroditic early in the first instar; occasional males arise from unfertilized eggs, but self-fertilization is assured by the protandry of the hermaphrodite. In the development of the ovotestis, initiation of the male phase is brought about by haploidization of those germ cells destined for spermatogenesis. In both Icerya zeteki and Icerya purchasi this gonial reduction results from the degeneration and elimination of one genome during prophase. Except for minor variations in the coiling cycle of spermatocytes, the chromosomes (n=2) of I. zeteki correspond closely to those of all other haplo-diploid iceryines known. The present status of the species Icerya zeteki Cockerell is reviewed, and on both taxonomicand cytological grounds is judged to be uncertain.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 1-21 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The pre-metaphase stretch is found to be a normal stage in male meiosis in six species of phasmids. 2. Its essential features are a precocious orientation of the kinetochores and their movement toward opposite poles of the developing spindle in first meiotic prophase, — with a consequent stretching of the chromosomes. It is followed by recontraction of the chromosomes and their movement to the equator. Attraction beween kinetochore and center, reinforced by the effect of elongation of the spindle, is considered responsible for the movements of the stretch. 3. The pre-metaphase stretch in phasmids differs from that of mantids in (1) its timing relative to meiotic stage, and (2) its expression in one species in the prophase of both meiotic divisions. 4. The distribution of the stretch in nature, and its significance for the mechanism of mitosis are discussed.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae). Segregational movements are interpolar, and are implemented through chromosomal fibers. Univalent autosomes, present from diakinesis on in several species, are capable of a similar distance segregation in prometaphase. The sex chromosomes are XX ♀ —XY ♂, as is characteristic of the Order, with the exception of Entanoneura phthisica in which both elements are compound —X1X2X3Y1Y2Y3in the male, and X1X1X2X2X3X3 in the female. In tetraploid sectors of gonial origin in testes of this species no sex bivalents are formed; a distance segregation of 6 sex univalents to each pole is effected, but — as observed in the one individually identifiable pair — segregation separates complete homologues, Y1 from Y1, X1 from X1, etc. In all species the male meiotic spindle is formed by the collocation of individual chromosomal spindle units within which bivalents become deformed; the timing and degree of deformation vary with the species. In karyotype the American species conform to a common pattern with the known Japanese and European species; diploid numbers range only from 18 to 22, and each complement carries the family insigné of one pair of disproportionately large autosomes in a set of small and rather uniformly sized chromosomes.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 12 (1961), S. 327-350 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary (1) Breakage of chromosomes was induced by X-rays in adult and nymphal males of Euschistus servus, E. tristigmus and Solubea pugnax (Pentatomidae; Hemiptera-Heteroptera). (2) The diffuse nature of the kinetochore is demonstrated by the ability of chromosome fragments to perpetuate themselves mitotically through many cell generations of spermatogonia. (3) Free fragments, when not immobilized by the effects of radiation, are also capable of meiotic mitosis. A holokinetic, rather than a telomeric, nature is thus demonstrated for the meiotic restriction of kinetochore activity to chromosome ends, normal for Heteroptera and certain other Hemiptera. (4) Simple fragmentation as a factor in the evolution of compound sex chromosomes is supported by the observation that fragments of the X chromosome co-orient with the Y in a typical “touch and go” pairing. (5) The results are discussed with relation to problems of kinetochore structure and mitosis.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The asymmetry of karyotype previously regarded as a Family character of the Mantispidae is absent in 4 species representative of one of the species-groups tyxonomically distinguishable in the Mantispas of the Western Hemisphere. Further diversity is evident in the evolutionary loss of the Y chromosome in Plega dactylota Rehn and the substitution of a Neo-XY system for distance segregation in P. signata (Hagen). In the Mantispas pseudo- or “sticky” sex-bivalents are present at diakinesis with a maximum frequency of 50% in M. fuscicornis Banks. By final metaphase this is reduced to 2% or less except in M. uhleri Banks in which 6% of the spermatocytes retain sex-bivalents. Univalent autosomes, observed in all but one of the species studied, occur in less than 1% of the cells at first metaphase except in M. interrupta Say and Plega dactylota in which their frequency approaches 8%. The precocious segregation of these unconjoined autosomes shows that univalency, rather than any sex-related attribute, underlies distance segregation.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 88 (1983), S. 256-264 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In a single male specimen of Myrmeleon mexicanum Banks the sex chromosomes, normally X and Y, were replaced by what appeared to be X1X2 and Y. These segregated as expected on that interpretation in only half of the spermatocytes — in the other half, one X and the Y segregated from the other X. This atypical segregation is explicable on the assumption that one of the supposed Xs is a supernumerary, not a sex chromosome, and the diploid complement of the male comprises six pairs of autosomes plus a supernumerary and the X and Y sex chromosomes. The orientation of the X chromosomes at first metaphase was variable: kinetochoric activity may be localized midway the length of the chromosome, as in gonial mitosis, or terminally. Comparative study of three congeneric species, seven of Brachynemurus, one of Psammoleon, and one of Vella showed normal segregation in all, and no evidence for secondary kinetochoric activity. In nine of the species studied one pair of autosomes was unconjoined at first metaphase in 0.3%–1.2% of primary spermatocytes. These autosomes segregated precociously with the sex chromosomes in the central unit of the spindle. In one exceptional male of Brachynemurus hubbardi Currie all first meiotic metaphases showed this behavior, and a compound X1X2/Y1Y2 system was thus simulated. Bivalent formation replaced distance segregation of sex chromosomes in 0.4%–3.2% of the spermatocytes in seven of the thirteen species studied. These sex-bivalents frequently displayed partial or complete failure in congression.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 257-270 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 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.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The mantidLiturgousa sp. n. of Trinidad, B. W. I., although in external morphology practically indistinguishable fromL. maya, is cytologically distinct from all other species thus far studied.L. sp. n. has 21 chromosomes (2n ♂),L. maya 17,L. actuosa 23 andL. cursor 33. 2. Although the total length of all the chromosomes of the complement is approximately the same in all four species, the DNA content of the spermatid nucleus, microspectrophotometrically determined, differs to a striking degree. Nuclei ofL. sp. n. andL. actuosa carry one and one half times as much DNA as do those ofL. maya andL. cursor. 3. The significance of these findings is discussed with reference to evolutionary relationships within the genus.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The chromosomes of the African scale, Aspidoproctus maximus Louns., number 5 in the male, 6 in the female; sex chromosomes are of the XO male, XX female type. 2. Male meiosis is similar to that found in the Neotropical Llaveiini, with vesiculation of prophase nuclei, broadly dispersed polar centers, and divergent chromosomal fibers. The usual sequence of co-orientation and auto-orientation in meiosis is inverted; the chromosomes are autooriented at Metaphase I, and co-oriented at Metaphase II. 3. Asynapsis of one pair of autosomes occurs in from 14% to 52% (in different individuals) of the primary spermatocytes. Regular segregation of asynaptic chromosomes is ensured by a secondary pairing during interkinesis. 4. In spermiogenesis the chromosomes, linearly aligned, move out of the nucleus into the tail filament which forms a non-flagellated sperm.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...