Salivary Gland Chromosomes Research Articles

SetDB1 and Su(var)3-9 are essential for late stages of larval development of Drosophila melanogaster.

Methylation of H3K9 histone residue is a marker of gene silencing in eukaryotes. Three enzymes responsible for adding this modification - G9a, SetDB1/Egg, and Su(var)3-9 - are known in Drosophila. To understand how simultaneous mutations of SetDB1 and Su(var)3-9 may affect the fly development, appropriate combinations were obtained. Double mutants egg; Su(var)3-9 displayed pronounced embryonic lethality, slower larval growth and died before or during metamorphosis. Analysis of transcription in larval salivary glands and wing imaginal disks indicated that the effect of double mutation is tissue-specific. In salivary gland chromosomes, affected genes display low H3K9me2 enrichment and are rarely bound by SetDB1 or Su(var)3-9. We suppose that each of these enzymes directly or indirectly controls its own set of gene targets in different organs, and double mutation results in an imbalanced developmental program. This also indicates that SetDB1 and Su(var)3-9 may affect transcription via H3K9-independent mechanisms. Unexpectedly, in double and triple mutants, amount of di- and tri-methylated H3K9 is drastically reduced, but not completely absent. We hypothesize that this residual methylation implies the existence of additional H3K9-specific methyltransferase in Drosophila.

Cytological Approaches to Visualize Intracellular Dynamics of RNA-Binding Proteins at Active Genes in Drosophila.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a family of RNA-binding proteins that modulate multiple aspects of gene activity and RNA processing, including transcription, splicing, localization, translation, and decay of RNA. Interaction of hnRNPs with RNA is a highly dynamic but regulated process. Poly(ADP-ribose) polymerase (PARP)-dependent PARylation of different hnRNPs is a well-known posttranslational modification that affects their interactions with RNA. Here, we described a protocol for in situ localization of RNA-binding proteins (RBPs) on giant polytene chromosomes in Drosophila larval salivary glands, which have been widely used to visualize the dynamic binding profiles of various RBPs and other transcription-related proteins at specific loci on chromosomes. This chapter also includes a stepwise description of RNA:RNA in situ hybridization, in conjunction with immunostaining, using polytene chromosome squashes or intact tissues. We also highlight advanced live cell imaging methods, including FRAP and FLIP, using transgenic lines that express fluorescent-tagged hnRNPs. These cytological approaches can be used to visualize the localization of RNA-binding proteins and their interacting RNAs under different cellular conditions.

Teflon promotes chromosomal recruitment of homolog conjunction proteins during Drosophila male meiosis.

Meiosis in males of higher dipterans is achiasmate. In their spermatocytes, pairing of homologs into bivalent chromosomes does not include synaptonemal complex and crossover formation. While crossovers preserve homolog conjunction until anaphase I during canonical meiosis, an alternative system is used in dipteran males. Mutant screening in Drosophila melanogaster has identified teflon (tef) as being required specifically for alternative homolog conjunction (AHC) of autosomal bivalents. The additional known AHC genes, snm, uno and mnm, are needed for the conjunction of autosomal homologs and of sex chromosomes. Here, we have analyzed the pattern of TEF protein expression. TEF is present in early spermatocytes but cannot be detected on bivalents at the onset of the first meiotic division, in contrast to SNM, UNO and MNM (SUM). TEF binds to polytene chromosomes in larval salivary glands, recruits MNM by direct interaction and thereby, indirectly, also SNM and UNO. However, chromosomal SUM association is not entirely dependent on TEF, and residual autosome conjunction occurs in tef null mutant spermatocytes. The higher tef requirement for autosomal conjunction is likely linked to the quantitative difference in the amount of SUM protein that provides conjunction of autosomes and sex chromosomes, respectively. During normal meiosis, SUM proteins are far more abundant on sex chromosomes compared to autosomes. Beyond promoting SUM recruitment, TEF has a stabilizing effect on SUM proteins. Increased SUM causes excess conjunction and consequential chromosome missegregation during meiosis I after co-overexpression. Similarly, expression of SUM without TEF, and even more potently with TEF, interferes with chromosome segregation during anaphase of mitotic divisions in somatic cells, suggesting that the known AHC proteins are sufficient for establishment of ectopic chromosome conjunction. Overall, our findings suggest that TEF promotes alternative homolog conjunction during male meiosis without being part of the final physical linkage between chromosomes.

Polytene Chromosomes of Zaprionus Vittiger Coquillett

The karyotype of Zaprionus vittiger consists of six chromosomes, five of which are banded polytene arms extendingfrom a chromocentre in squashed preparations of the salivary glands. The sixth appears as a heterochromaticprotrusion. The chromosomes are acrocentric and joined together at heterochromatin around the centromereto form a chromocenter which is easily broken. Zaprionus vittiger Coquillett were trapped in the university ofLags botanical Garden. Salivary glands chromosomes of Zaprionus vittiger Coquillett third instar larvae wereprepared and examined under the microscope. The examination focused on the structure and characteristics of theterminal ends of different chromosomes which can be used to identify them in Zaprionus vittiger salivary glandschromosomes preparations.

Long-term retainment of some chromosomal inversions in a local population of Belgica antarctica Jacobs (Diptera, Chironomidae)

Genome of antarctic endemic Belgica antarctica Jacobs has been sequenced. However, no set of inversion diagnostic markers has ever been assigned for the species. Using the classical method of polytene chromosome squash preparation, we found three heterozygous inversions located on the second (two heterozygous inversions) and third chromosomes (one heterozygous inversion) in the Belgica antarctica population of a cape of Wiencke Island, 500 m to SW from Port Lockroy. The chromosome set and chromosome variability did not differ from those described in the literature (Atchley and Davis 1979). Every salivary gland chromosome had its own markers by which it can be determined. However, we did not find a sex-linked inversion on chromosome III and heterozygous inversion on chromosome I, reported in earlier studies. For the first time, we observed a strong heterochromatin band in chromosome III at the telomere of one arm. Our data show not only the stability of the described inversions in the population but also the usefulness of the squash preparation technique in the studies of genetic variability of Belgica antarctica in present time.

Identification of the Sibling Species of the Blackfly, Simulium damnosum Complex Using their Polytene Chromosomal Banding Patterns in Oji River System, Enugu State, Nigeria

Identification of the sibling species of the blackfly, S. damnosum complex using their polytene chromosomal banding patterns in Oji river system was carried out with the aim of accurately identifying the particular sibling species of S. damnosum complex involved in the transmission of onchocerciasis in Oji-river LGA and environ. Simulium damnosum complex larvae were collected monthly in forty eight (48) breeding sites in four sampling units for three years in the Oji river system in wet and dry seasons. Collected larvae were preserved in cold Carnoy’s solution prior to processing. Salivary gland chromosomes were extracted, processed and analyzed microscopically for polytene chromosomal banding patterns. Three sibling species of Simulium damnosum complex that breed in the Oji river system were identified in varying degrees. They included S. squamosum, S. yahense and S. damnosum sensu stricto (s.s.). Variation in the occurrence of the sibling species was statistically significant. Dry and wet season catches for all the sibling species in the sampling units were found to differ statistically. The identified sibling species of S. damnosum complex are known to be vectors of Onchocerca volvulus, the causative agent of onchocerciasis, a disease highly prevalent in Oji-river LGA and environ.

SetDB1 and Su(var)3-9 play non-overlapping roles in somatic cell chromosomes of Drosophila melanogaster

We explored functional roles of two H3K9-specific histone methyltransferases SetDB1 and Su(var)3-9. Using DamID approach, we generated the binding profile for SetDB1 in Drosophila salivary gland chromosomes, and matched it to the profile of Su(var)3-9. Unlike Su(var)3-9, SetDB1 turned out to be an euchromatic protein that is absent from repeated DNA compartment, and is largely restricted to TSSes and 5'UTRs of ubiquitously expressed genes. Significant SetDB1 association is also observed at insulator protein CP190 binding sites. SetDB1 and H3K9me2/3-enriched sites tend to display poor overlap. At the same time, SetDB1 has clear connection with the distribution of H3K27me3 mark. SetDB1 binds outside the domains possessing this modification, and about half of the borders of H3K27me3 domains are decorated by SetDB1 together with actively transcribed genes. On the basis of poor correlation between the distribution of SetDB1 and H3K9 methylation marks, we speculate that in somatic cells, SetDB1 may contribute to the methylation of a broader set of chromosomal proteins than just H3K9. In addition, SetDB1 can be expected to play a role in the establishment of chromatin functional domains.

Using Digital Micro-network Interactive System to Improve the Quality of Experimental Teaching of Drosophila Salivary Gland Chromosomes

Background: With the microscopic interactive system widely used in experiment teaching of Genetics, Botany, Cell biology, Medical morphology, etc., which are focused on the microscopic observation, Traditional experimental teaching mode is changed, experimental teaching efficiency and experimental teaching effect are improving. Objective: In order to improve the efficiency and effect of genetics experiment teachingthis, we introduce the digital micro-network interactive system into the genetics experiment teaching. Method: We implemented the observation and preparation techniques of Drosophila salivary gland chromosomes from teaching organization, implementation of the experiment, using the digital micro-network interactive system. And the application effect of microinteractive system in chromosome section of Drosophila salivary gland is analyzed. Result: The results showed that the microscopic interaction system could improve the efficiency and effectiveness of the interaction between teachers and students, stimulate the students' experimental interest. Especially, the success rate of salivary gland chromosome is increased by more than 20%. Conclusion: The application of micro-interactive system has indeed revolutionized the traditional experimental teaching mode to a certain extent. It closely relies on modern information technology and forms a new experimental teaching mode for the cultivation of genetically innovative talents, which characterize by zero barriers in teacher-student interaction, zero distance in resource sharing and zero gap in real-time monitoring.

Physicochemical characteristics of the Dombrovska pit lake (Ukraine) formed in an opencast potassium salt mine and the genome response of Chironomus salinarius Kieffer (Chironomidae, Diptera) to these conditions

This study focuses on the Dombrovska pit lake, near the city of Kalush in Ukraine, which is a former potassium salt mine filled with brine and freshwater. The water level is still increasing and as a result the salinity is decreasing. We analyzed the benthic fauna communities and the genome instability by assessing the rearrangements in the polytene chromosomes of Chironomus salinarius and the physicochemical parameters of the near-bottom water (pH, conductivity, mineralization, major ions, NO3−, NH4+, metals Cd, Pb, Cu, Mn, and Fe) and sediment (pH, organic matter and metals Cd, Pb, Cu, Zn, Mn, and Fe) at four sites. The water mineralization ranged from 17.3 to 26.2 g dm−3 which are classified as mesohaline and polyhaline waters, respectively. The biodiversity of the benthic fauna was low, and the dominant species was C. salinarius. The density of C. salinarius varied spatially and changed from 637 ind./m2 at a depth of 5 m to 8167 ind./m2 at a depth of 2.5 m. The genome instability was analyzed by examining the structural and functional changes in the salivary gland chromosomes of C. salinarius. The exposure of C. salinarius damaged the chromosomes and the activities of key structures, such as the Balbiani ring and nucleolar organizer, were partially or completely suppressed.

Binding of SU(VAR)3-9 Partially Depends on SETDB1 in the Chromosomes of Drosophila melanogaster.

H3K9 methylation is known to play a critical role in gene silencing. This modification is established and maintained by several enzymes, but relationships between them are not fully understood. In the present study, we decipher the interplay between two Drosophila H3K9-specific histone methyltransferases, SU(VAR)3-9 and SETDB1. We asked whether SETDB1 is required for targeting of SU(VAR)3-9. Using DamID-seq, we obtained SU(VAR)3-9 binding profiles for the chromosomes from larval salivary glands and germline cells from adult females, and compared profiles between the wild type and SETDB1-mutant backgrounds. Our analyses indicate that the vast majority of single copy genes in euchromatin are targeted by SU(VAR)3-9 only in the presence of SETDB1, whereas SU(VAR)3-9 binding at repeated sequences in heterochromatin is largely SETDB1-independent. Interestingly, piRNA clusters 42AB and 38C in salivary gland chromosomes bind SU(VAR)3-9 regardless of SETDB1, whereas binding to the same regions in the germline cells is SETDB1-dependent. In addition, we compared SU(VAR)3-9 profiles in female germline cells at different developmental stages (germarium cells in juvenile ovaries and mature nurse cells). It turned out that SU(VAR)3-9 binding is influenced both by the presence of SETDB1, as well as by the differentiation stage.

The RNA helicase UPF1 associates with mRNAs co-transcriptionally and is required for the release of mRNAs from gene loci.

UPF1 is an RNA helicase that is required for nonsense-mediated mRNA decay (NMD) in eukaryotes, and the predominant view is that UPF1 mainly operates on the 3'UTRs of mRNAs that are directed for NMD in the cytoplasm. Here we offer evidence, obtained from Drosophila, that UPF1 constantly moves between the nucleus and cytoplasm by a mechanism that requires its RNA helicase activity. UPF1 is associated, genome-wide, with nascent RNAs at most of the active Pol II transcription sites and at some Pol III-transcribed genes, as demonstrated microscopically on the polytene chromosomes of salivary glands and by ChIP-seq analysis in S2 cells. Intron recognition seems to interfere with association and translocation of UPF1 on nascent pre-mRNAs, and cells depleted of UPF1 show defects in the release of mRNAs from transcription sites and their export from the nucleus.

Prodiamesa olivacea Meigen and Prodiamesa bureshi Michailova (Diptera, Chironomidae, Prodiamesinae) as a candidate for assessing the genotoxicity of trace metals in fluvial sediments.

The genome response, realized by structure chromosome rearrangements in the polytene chromosomes of two sibling species Prodiamesa bureshi Michailova and Prodiamesa olivacea Mg., was studied. The larvae of the species were collected in May and September, 2016, from Biała Przemsza River, a metal-mine-affected site in southern Poland, where Zn, Cd, and Pb concentrations in the sediment exceeded many times the reference data and those from unpolluted sites. The water had high contents of different major ions and nutrients. A high spectrum of somatic chromosome aberrations was detected in the salivary gland chromosomes of both species, which defined a high somatic index (from 1.2 to 7), indicating the sensitivity of both genomes to anthropogenic stress. The cells with somatic rearrangements of both species were significantly higher (P. bureshi: G = 25.636, P < 0.001 May, G = 32.722, P < 0.001 September; P. olivacea: G = 47.863, P < 0.001 May, G = 38.742, P < 0.001 September) than the control. Both species from polluted and unpolluted sites showed a high frequency of ectopic conjugations, as between arms B, CD (centromere regions), and E (NOR). Some deformities of mentum and mandibles of P. bureshi (20%) and P. olivacea (35%) were detected. We postulate that the appearances of somatic chromosome aberrations are more sensitive indicators of genotoxicity in the studied species than changes in external morphology. The sensitivity of the P. olivacea and P. bureshi genomes shows that these species are good candidates for detecting the presence of genotoxic compounds in aquatic basins and evaluating their genotoxic effects.

Genome instability in Chironomus annularius sensu Strenzke (Diptera, Chironomidae): A biomarker for assessment of the heavy metal contaminants in Poland

We studied the effect of heavy metal contaminations on genome instability of Chironomus annularius sensu Strenzke from three sampling sites on the River Chechło valley in southern Poland and a control site in Saraya, Bulgaria. The analysis of the heavy metal concentrations in sediments at the three river sites indicated concentrations higher than those in the fossil reference data (Zn 83-160 times, Pb 64-250 times, and Cd 210-793). According to the geoaccumulation index (Igeo), the sediments at all Chechło stations were classified as extremely polluted (Igeo class 6) by Cd, Pb and Zn while they were much less polluted by Cu (classes 1-3). The concentration of Cd, Pb and Zn in the sediments studied exceeded 21-79, 11-44 and 18-34 times the toxic effect threshold (TET) respectively; therefore, the sediments potentially have detrimental effects on the fauna. Genome instability was determined by somatic structural chromosome alterations (mainly heterozygous inversions) in the salivary gland chromosomes of C. annularius. On the basis of the number and frequency of these aberrations the somatic (S) and cytogenetic (C) indices were calculated as these indices allow a better quantification of the impact of heavy metals on organisms living in sediments. In the three Chechło sampling sites somatic aberrations occurred at a frequency significantly higher than in the control site (P&lt;0.001). The three Chechło samples possess a high spectrum of somatic rearrangements with S index varying from 1.5 to 2.23 while in control site, S is 1.08. The C index of C. annularius from the polluted river sites varied from 0.163 to 0.380, far in excess of the C value of the control site (1.0), indicating strong pollution (&lt;0.5) according to previous studies. In addition, a high level of inherited aberrations was detected (19 inherited band sequences, two of which were new). In all river stations the inverted homozygous band sequences A2.2 occurred in a high frequency (85%) and no standard sequences (A1.1) were observed. The transcription activity of Nucleolar Organizers (NORs) in chromosome arms A, C, E, G was often damaged and NOR activity was completely suppressed in 12.48% of larvae. Moreover, appearance of malformations in the external morphology of larvae was detected in 16.67% of larvae from all polluted sites. Therefore, the genome instability as estimated by two cytogenetic indices is a good biomarker of long-term toxicity and could be successfully implemented in the sediment monitoring procedures.

Similarity in replication timing between polytene and diploid cells is associated with the organization of the Drosophila genome.

Morphologically, polytene chromosomes of Drosophila melanogaster consist of compact “black” bands alternating with less compact “grey” bands and interbands. We developed a comprehensive approach that combines cytological mapping data of FlyBase-annotated genes and novel tools for predicting cytogenetic features of chromosomes on the basis of their protein composition and determined the genomic coordinates for all black bands of polytene chromosome 2R. By a PCNA immunostaining assay, we obtained the replication timetable for all the bands mapped. The results allowed us to compare replication timing between polytene chromosomes in salivary glands and chromosomes from cultured diploid cell lines and to observe a substantial similarity in the global replication patterns at the band resolution level. In both kinds of chromosomes, the intervals between black bands correspond to early replication initiation zones. Black bands are depleted of replication initiation events and are characterized by a gradient of replication timing; therefore, the time of replication completion correlates with the band length. The bands are characterized by low gene density, contain predominantly tissue-specific genes, and are represented by silent chromatin types in various tissues. The borders of black bands correspond well to the borders of topological domains as well as to the borders of the zones showing H3K27me3, SUUR, and LAMIN enrichment. In conclusion, the characteristic pattern of polytene chromosomes reflects partitioning of the Drosophila genome into two global types of domains with contrasting properties. This partitioning is conserved in different tissues and determines replication timing in Drosophila.

A standard photomap of ovarian nurse cell chromosomes and inversion polymorphism in Anopheles beklemishevi

BackgroundAnopheles beklemishevi is a member of the Maculipennis group of malaria mosquitoes that has the most northern distribution among other members of the group. Although a cytogenetic map for the larval salivary gland chromosomes of this species has been developed, a high-quality standard cytogenetic photomap that enables genomics and population genetics studies of this mosquito at the adult stage is still lacking.MethodsIn this study, a cytogenetic map for the polytene chromosomes of An. beklemishevi from ovarian nurse cells was developed using high-resolution digital imaging from field collected mosquitoes. PCR-amplified DNA probes for fluorescence in situ hybridization (FISH) were designed based on the genome of An. atroparvus. The DNA probe obtained by microdissection procedures from the breakpoint region was labelled in a DOP-PCR reaction. Population analysis was performed on 371 specimens collected in 18 locations.ResultsWe report the development of a high-quality standard photomap for the polytene chromosomes from ovarian nurse cells of An. beklemishevi. To confirm the suitability of the map for physical mapping, several PCR-amplified probes were mapped to the chromosomes of An. beklemishevi using FISH. In addition, we identified and mapped DNA probes to flanking regions of the breakpoints of two inversions on chromosome X of this species. Inversion polymorphism was determined in 13 geographically distant populations of An. beklemishevi. Four polymorphic inversions were detected. The positions of common chromosomal inversions were indicated on the map.ConclusionsThe study constructed a standard photomap for ovarian nurse cell chromosomes of An. beklemishevi and tested its suitability for physical genome mapping and population studies. Cytogenetic analysis determined inversion polymorphism in natural populations of An. beklemishevi related to this species’ adaptation.

Geographic structure of sibling species and cytotypes of the Simulium arcticum complex (Diptera: Simuliidae) in rivers of central Idaho and southeastern Washington, United States of America

AbstractWe made 37 collections and analysed the polytene chromosomes of salivary glands of 726 larvae of the Simulium arcticum Malloch (Diptera: Simuliidae) complex from 10 locations in an unstudied region from central Idaho and southeastern Washington, United States of America. We compared our results to previous population cytotaxonomic research on larvae of this complex from western Montana, northern Idaho, and eastern Washington, United States of America. We identified four sibling species, S. brevicercum Knowlton and Rowe, S. saxosum Adler, S. arcticum sensu stricto, S. apricarium Adler, Currie, and Wood; and three cytotypes, S. arcticum IIL-9, IIL-17, and IIL-79, previously described by us. We discovered a new cytotype, S. arcticum IIL-80, at three locations in the western region of our sample area. We also found combinational (ancestral) types between S. saxosum and S. arcticum sensu stricto and between S. saxosum and S. arcticum IIL-79, suggesting that ancestral populations of the complex still exist. Geographic structuring of these sibling species and cytotypes are documented given that S. saxosum occurred in western regions, S. arcticum IIL-79 in northeastern regions, and S. apricarium in southeastern regions of our study area.

Thiazole Orange as an Alternative to Antibody Binding for Detecting Triple-helical DNA in Heterochromatin of Drosophila and Rhynchosciara.

The standard method for detecting triple-stranded DNA over the last 1.5 decades has been immune detection using antibodies raised against non-canonical nucleic acid structures. Many fluorescent dyes bind differentially to nucleic acids and often exhibit distinctive staining patterns along metaphase chromosomes dependent upon features, including binding to the major and minor DNA grooves, level of chromatin compaction, nucleotide specificity, and level of dye stacking. Relatively recently, the fluorochrome Thiazole Orange (TO) was shown to preferentially bind to triplex DNA in gels. Here, we demonstrate that TO also detects triplex DNA in salivary gland chromosomes of Drosophila melanogaster and Rhynchosciara americana identical in location and specificity to observations using antibodies. This finding may enable triple-stranded DNA investigations to be carried out on a much broader and reproducible scale than hitherto possible using antibodies, where a frequently encountered problem is the difference in detection specificity and sensitivity between one antibody and another.

Chironomus alchichica sp. n. (Diptera: Chironomidae) from Lake Alchichica, Mexico.

Morphological analysis of all developmental stages (except female), mitochondrial DNA sequences from cytochrome c oxidase subunit I (cox1) and cytological analysis of the polytene chromosomes were used to describe a new species of Chironomus found in the littoral and profundal zones of an endorheic, warm-monomictic lake in Mexico. Male imago is distinguished by the shape of superior volsella and by an antennal and bristle ratio lower than two. The pupa is characterized by the spur morphology of abdominal segment VIII. There is also a continuous row of hooklets on abdominal segment II. The larva is distinguished by a combination of antenna, mentum, mandible, and pecten epipharyngis characteristics, and abdominal ventral tubules. Molecular and cytological analysis supported the morphological differences found. The maximum likelihood tree obtained shows that Chironomus alchichica sp. n. clusters together with Chironomus decorus-group sp. 2 Butler et al. (1995) (bootstrap support = 92%), but genetic p-distances within C. alchichica sp. n. (0.004) were lower than the p-distances between other species of the decorus-group (C. decorus-group sp. 2, Chironomus bifurcatus Wülker et al., 2009 and Chironomus maturus Johannsen, 1908) confirming that it is a different species. The new species belongs to thummi cytocomplex, (decorus-group), with chromosome set- 2n = 8 and chromosome arm combinations: AB CD EF G. Karyologically, the species is closest to Chironomus riihimaekiensis Wülker (1973). This species has very compact salivary gland chromosomes with well heterochromatinized centromere regions in chromosomes AB CD G. Several fixed homozygous inversions distinguish arm A of the species from that of C. riihimaekiensis. Arm E differs from that of C. riihimaekiensis by simple fixed homozygous inversion. Some similarities in band sequences of this arm were found with species from the decorus-group as Chironomus blaylocki Wülker et al., 2009 and C. bifurcatus (decorus-group). The position of the key constrictions in chromosome G: Nucleolar organizer (NOR) and Balbiani rings (BRs) is similar to the species of decorus-group. C. alchichica sp. n. has been found in soft sediments rich in organic matter in well mineralized waters (where conductivity >10 mS cm-1) and with a high pH (≥9). The profundal zone is inhabited only during the mixing period, when dissolved oxygen is present.

The Karyotype and External Morphology of Stictochironomus sticticus (Fabricius, 1781) (Diptera: Chironomidae) from Poland

This paper presents the karyotype and external morphology of larva, pupa and adult male of Stictochironomus sticticus (Fabricius, 1781) from Poland. The species of the genus Stictochironomus are generally identified on the basis of pupal and adult morphology. However, the species described in this paper has species-specific markers in the salivary gland chromosomes which allow identification at the larval stage. Karyological markers are evaluated for the Polish population in comparison with other European populations and Stictochironomus species.

Advances in understanding Drosophila salivary gland polytene chromosome and its applications in genetics teaching

Drosophila salivary gland polytene chromosome, one of the three classical chromosomes with remarkable characteristics, has been used as an outstanding model for a variety of genetic studies since 1934. The greatest contribution of this model to genetics has been providing extraordinary angle of view in studying interphase chromosome structure and gene expression regulation. Additionally, it has been extensively used to understand some special genetic phenomena, such as dosage compensation and position-effect variegation. In this paper, we briefly review the advances in the study of Drosophila salivary gland chromosome, and try to systematically and effectively introduce this model system into genetics teaching practice in order to steer and inspire students' interest in genetics.