Insect sex chromosomes (original) (raw)
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Absence of sex chromatin corresponds with a sex-chromosome univalent in females of Trichoptera
Eje, 2013
Five Trichoptera species, representing four different families of three suborders, have been ex amined for sex chromatin status in relation to their sex chromosome system. These were Hydropsyche sp., Polycentropus flavomaculatus (Pictet), Rhyacophila sp., Anabolia furcata Brauer and Limnephilus decipi ens (Kolenatý). None of the species displayed sex-specific heterochromatin in highly polyploid nuclei of the Malpighian tubule cells. Such sex chromatin is a characteristic trait of the heterogametic female sex in the sister order Lepidoptera; it is derived from the heterologous sex chromosome W. Hence, the absence of sex chromatin in somatic nuclei of Trichoptera females indicated the lack of a W chromosome in their karyotype. Correspondingly, diploid chromosome sets of the females consisted of an odd chromosome number, two sets of autosomes and one sex chromosome Z. Thus, the Z/ZZ chromosome mechanism of sex determination has been confirmed. In pachytene and postpachytene oocytes, the Z chromosome hav ing no pairing partner formed a univalent. In Hydropsyche sp., the Z-univalent was distinct as a compact, positively heteropycnotic element. Whereas, in two other caddis-flies, P. flavomaculatus and L. decipiens, it formed a negatively heteropycnotic thread. In postpachytene nuclei of nurse cells of A. furcata, two sis ter chromatids of the Z chromosome separated as a result of chromosome degeneration and formed a negatively heteropycnotic pseudobivalent. The species-specific differences in pycnosis may reflect a tran scriptional activity/inactivity of the Z chromosome during meiotic prophase. The absence of sex chroma tin and the sex chromosome system in Trichoptera are characters in common with the "primitive" Lepidoptera. This supports a hypothesis that the common ancestor of both orders had a Z/ZZ sex chromo some mechanism.
Entomological Science, 2018
Many species of grasshopper have an XX/XO sex chromosome system, including Tropidacris cristata grandis (23, XX/XO). The X chromosome behaves differently from the autosomes, but little is known about its origin and molecular composition. To better understand the genomic composition and evolutionary processes involved in the origin of the sex chromosomes, we undertook an analysis of its meiotic behavior, heterochromatin distribution and microdissection in T. c. grandis. Analysis of meiotic cells revealed a difference in the behavior of the X chromosome compared to the autosomes, with different patterns of condensation and cellular arrangement. Heterochromatic terminal blocks were predominant. The chromosome painting revealed a bright block in the centromeric/pericentromeric region of the X chromosome and slight markings in the other regions. In the autosomes, the X chromosome probe hybridized in the centromeric/pericentromeric region, and hybridization signals on terminal regions cor...
Sex chromatin and sex chromosome systems in nonditrysian Lepidoptera (Insecta)
Journal of Zoological Systematics and Evolutionary Research, 2000
Eleven representatives of the superorder Amphiesmenoptera "Trichoptera ¦ Lepidoptera# were examined for sex chromatin status[ Three species represent stenopsychoid\ limnephiloid and leptoceroid branches of the Trichoptera^eight species belong to the primitive\ so!called nonditrysian Lepidoptera and represent the infra!orders Zeugloptera\ Dacnonypha\ Exoporia\ Incurvariina\ Nepticulina and Tischeriina[ The female!speci_c sex chromatin body was found in the interphase somatic nuclei of Tischeria ekebladella "Bjerkander 0684# "Lepidoptera\ Tischeriina#[ The sex chromatin was absent in all investigated Trichoptera species as well as in all representatives of the nonditrysian Lepidoptera except Tischeria ekebladella[ The sex chromosome mechanism of Limnephilus lunatus Curtis 0723 "Trichoptera\ Limnephilidae# is Z:ZZ[ The sex chromosome mechanism of Tischeria ekebladella "Lepidoptera\ Tischeriina# is ZW:ZZ including the W chromosome as the largest element in the chromosome set[ The data obtained support the hypothesis that the Z:ZZ sex chromosome system\ the female heterogamety and the absence of the sex chromatin body in interphase nuclei are ancestral traits in the superorder Amphiesmenoptera[ These ancestral characters are probably kept constant in all the Trichoptera and in the most primitive Lepidoptera[ The W sex chromosome and the sex chromatin evolved later in the nonditrysian grade of the Lepidoptera[ It is proposed that the sex chromatin is a synapomorphy of Tischeriina and Ditrysia[
Genome, 2005
We performed a detailed karyotype analysis in the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), the key pest of pome fruit in the temperate regions of the world. The codling moth karyotype consisted of 2n = 56 chromosomes of a holokinetic type. The chromosomes were classified into 5 groups according to their sizes: extra large (3 pairs), large (3 pairs), medium (15 pairs), small (5 pairs), and dot-like (2 pairs). In pachytene nuclei of both sexes, a curious NOR (nucleolar organizer region) bivalent was observed. It carried 2 nucleoli, each associated with one end of the bivalent. FISH with an 18S ribosomal DNA probe confirmed the presence of 2 clusters of rRNA genes at the opposite ends of the bivalent. In accordance with this finding, 2 homologous NOR chromosomes were identified in mitotic metaphase, each showing hybridization signals at both ends. In highly polyploid somatic nuclei, females showed a large heterochromatin body, the so-called sex chromatin or W chromatin. The heterochromatin body was absent in male nuclei, indicating a WZ/ZZ (female/male) sex chromosome system. In keeping with the sex chromatin status, pachytene oocytes showed a sex chromosome bivalent (WZ) that was easily discernible by its heterochromatic W thread. To study molecular differentiation of the sex chromosomes, we employed genomic in situ hybridization (GISH) and comparative genomic hybridization (CGH). GISH detected the W chromosome by strong binding of the Cy3-labelled, female-derived DNA probe. With CGH, both the Cy3-labelled female-derived probe and Fluor-X labelled male-derived probe evenly bound to the W chromosome. This suggested that the W chromosome is predominantly composed of repetitive DNA sequences occurring scattered in other chromosomes but accumulated in the W chromosome. The demonstrated ways of W chromosome identification will facilitate the development of genetic sexing strains desirable for pest control using the sterile insect technique.
Chromosome Research, 2007
Nucleolus organizer regions (NORs) and nucleolus locations were studied after silver staining in spermatocytes at pachynema from four beetle species selected for their various combinations of sex chromosomes. Their karyotypic formulae were: 18,neoXY (Dorcus parallelipipedus); 25,X (Passalus unicornis) and 20,Xyp (Cetonia aurata and Protaecia (Potosia) opaca). NORs were located in the short arms of a unique acrocentric autosome pair in the first three and in intercalary position in a sub-metacentric autosome pair in the last species. Silver staining gave remarkably more consistent results in pachytene than in mitotic spreads, enabling the detection of both NORs and nucleoli, and also better results in embryo than in spermatogonial metaphases. At pachynema the NORs were elongated, roughly in proportion to the number of nucleoli, which always remained associated with NOR. Nucleoli were not recurrently associated with sex chromosomes, except in P. unicornis, at late pachynema. In C. aurata and P. opaca the sex body was recurrently associated with acrocentric short arms and metacentric telomeres, respectively. Even in these simple situations, with NORs located in a single autosome pair, the number of nucleoli and their relationships with sex chromosomes varied strongly from species to species. These variations appear to be largely determined by the chromosome rearrangements which have occurred during evolution, which makes extrapolations and generalizations quite hazardous. In D. parallelipipedus pachytene cells a quasi-systematic and transient fusion between the terminal heterochromatin of two sub-metacentrics was detected. Other chromosome bivalents could also be occasionally associated, but not the NOR carrier one. A strong enhancement of DAPI or quinacrine mustard staining was observed at the fusion point.
Genetics and Molecular Biology, 2010
Spittlebugs annually infest pastures and cause severe damage, representing a serious problem for the tropical American beef cattle industry. Spittlebugs are an important biotic constraint to forage production and there is a lack of cytogenetic data for this group of insects. For these reasons, we conducted this work, in which the spermatogenesis and nucleolar behavior of Deois flavopicta, Mahanarva fimbriolata and Notozulia entreriana were studied. The males possessed testes in the shape of a "bunch of grapes"; a variable number of testicular lobes per individual and polyploid nuclei composed of several heteropycnotic bodies. A heteropycnotic area was located in the periphery of the nucleus (prophase I); the chiasmata were terminal or interstitial; metaphases I were circular or linear and anaphase showed late migration of the sex chromosome. The chromosome complement had 2n = 19, except for N. entreriana (2n = 15); the spermatids were round with heteropycnotic material in the center and elongated with conspicuos chromatin. The analysis of testes after silver nitrate staining showed polyploid nuclei with three large and three smaller nucleolar bodies. Early prophase cells had an intensely stained nucleolar body located close to the chromatin and another less evident body located away from the chromatin. The nucleolar bodies disintegrated during diplotene. Silver staining occurred in two autosomes, in terminal and subterminal locations, the latter probably corresponding to the nucleolus organizer regions (NORs). The spermatids were round with a round nucleolar body and silver staining was observed in the medial and posterior region of the elongated part of the spermatid head.
Use of meiotic pachytene stage of spermatocytes for karyotypic studies in insects
Chromosome Research, 2006
Coleopterans represent by far the largest animal group, with more than 300,000 identified species. Only little progress in their chromosome analysis has been accomplished during recent decades, compared with that made in vertebrate cytogenetics. Both the small size of their genome and the difficulty of obtaining mitotic cells with nice chromosomes have limited the application of conventional techniques, such as chromosome banding. A method for obtaining chromosome banding on well-spread bivalents from the pachytene stage of the meiotic prophase, the most frequent stage in young imagines, is described. It makes possible the identification of all bivalents and the establishment of the karyotype with greater ease and accuracy than with mitotic cells. In addition, it gives some insight into chromosome organization at a stage when autosomes are assumed to undergo an intense transcriptional activity. The results of the technique, which was successfully applied to many species, are described here in two of them, Cetonia aurata and Adesmia montana as examples.