PubMed Health⌕ Search

Biomedical subjects

S K Narang

Publications and source records attributed to S K Narang.

At least 19 recordsLinked to original sources
PubMed1994

Transposable elements in lepidoptera: hobo-like transposons in Heliothis virescens and Helicoverpa zea.

In the present study, a PCR-based approach was undertaken to determine if members of the hobo-like family of transposable elements were identifiable within the genomes of a number of diverse species, including Heliothis virescens and Helicoverpa zea. The amplified products derived from both H. virescens and H. zea were cloned and characterized. Analysis of the DNA sequence and the single open reading frame found within these fragments clearly demonstrates that these elements are closely related to the hobo transposon from Drosophila melanogaster. In addition, amino acid sequence analysis of the members of this family defines consensus, specific amino acids found within similar regions of all members of this transposon family.

Amino Acid Sequence↗
PubMed1993

Genetic evidence for the existence of cryptic species in the Anopheles albitarsis complex in Brazil: allozymes and mitochondrial DNA restriction fragment length polymorphisms.

Allozyme and mitochondrial DNA (mtDNA) restriction studies were undertaken to determine the extent of genetic divergence among field populations of Anopheles albitarsis in Brazil. Two sympatric species, An. deaneorum and An. marajoara, were identified in collections from Costa Marques (CM), Rondonia. Genetic evidence includes (1) the presence of two types of individuals, each with diagnostic allelic clusters (for Had-1, Pgi-1, Pep-1, Mpi-1, and Idh-1), (2) a deficiency of heterozygotes, and (3) characteristic mtDNA haplotypes. In addition, two allopatric cryptic species of An. marajoara were identified, one from Iguape (An. marajoara form IG), Sao Paulo state, and the other from the Island of Marajo (An. marajoara form MA). Though form IG and form-MA resemble form CM in wing spot morphology, they differ from it in diagnostic allozymes and mtDNA haplotypes. An. marajoara form CM had a higher variability (mean heterozygosity, H = 0.22, and percentage of polymorphic loci, P = 66.7) than did form IG and form MA (H = 0.08 in both, and P = 25.0 and 33.3, respectively). Form MA and form IG are genetically more similar to each other than both are to form CM. Based on wing morphology, estimates of F statistics, and genetic similarities, we propose that An. albitarsis in Brazil is a species complex. It comprises at least two morphologically distinguishable species: (1) An. deaneorum (currently one taxon) and (2) the An. marajoara species complex, which further consists of at least three cryptic forms, marajoara form MA, marajoara form IG, and marajoara form CM.

Alleles↗
PubMed1993

Multiple-technique identification of sibling species of the Anopheles quadrimaculatus complex.

In the past, most researchers used a single technique for identification of cryptic taxa, population structures, biosystematics, and phylogenetic studies. Our experience with the Anopheles quadrimaculatus complex shows the importance of using several methods on individual mosquitoes. This approach consists of analysis of the polytene chromosomes in ovarian nurse cells, gas chromatographic profiles of cuticular hydrocarbons, isozyme electrophoresis, and restriction site analysis of mitochondrial or genomic DNA. We recommend use of this multiple-technique approach when analyzing feral populations for the first time, or for correlating information obtained by investigators using different techniques.

Animals↗
PubMed1992

Mitochondrial and ribosomal DNA variation among members of the Anopheles quadrimaculatus (Diptera: Culicidae) species complex.

The extent of intra- and inter-specific variation in mitochondrial DNA and nuclear ribosomal RNA gene restriction sites was determined for the four sibling species of the Anopheles quadrimaculatus complex. Individual mosquitoes were identified by allozyme analysis according to previously published keys, and the total genomic DNA of these same individuals was then cleaved with restriction enzymes. Restriction maps of mitochondrial DNA, including the positions of variable sites, were constructed for each species. No evidence for interspecific hybridization was found in the populations surveyed. There was little variation in restriction patterns within any given species, but differences occurred among the four. Three restriction enzymes (AvaI, HindIII, and PvuII) yielded species-specific DNA restriction patterns for the mitochondrial DNA, while AvaI and HindIII produced diagnostic patterns for the ribosomal DNA. Thus, restriction patterns were very useful for detecting cryptic species but less appropriate than isozymes for studying genetic structure of populations within species.

Animals↗
PubMed1992

Comparative susceptibility of species A, B and C of Anopheles quadrimaculatus complex to infection with subperiodic Brugia malayi and Brugia pahangi (Nematoda: Filarioidea).

Susceptibilities of natural populations of sibling species A, B and C of the Anopheles quadrimaculatus complex and the colonized strain A to subperiodic Brugia malayi and Brugia pahangi were compared. All 3 sibling species showed varying degrees of susceptibility to both B. pahangi and B. malayi, and they were considerably more susceptible to B. pahangi than to B. malayi. The rate and intensity of infection to B. pahangi were highest for species A (66.2% and 7.4 L3/female, respectively) and lowest for species B (21.3% and 1.7 L3/female). For B. malayi these values were higher for species A (29.7% and 1.84 L3/female) than for species B (13.3% and 0.86 L3/female) and C (12.6% and 0.75 L3/female). The colonized strain A of An. quadrimaculatus was significantly more susceptible to both Brugia species than the natural populations of sibling species A, B and C.

Animals↗
PubMed1991

Diagnostic characterization of Anopheles freeborni and An. hermsi by hybrid crosses, frequencies of polytene X chromosomes and rDNA restriction enzyme fragments.

A polytene chromosome analysis was prepared from Anopheles freeborni collected from 25 locations in north and central California, and parts of Washington and Oregon. The X chromosome banding pattern, thought previously to be specific to An. hermsi, was common in mosquitoes collected from foothill regions in California, and in all samples from Washington and Oregon. At some of these locations, many mosquitoes had heterokaryotypes for the inversion that distinguishes the X chromosome of An. freeborni from that of An. hermsi. Use of rDNA restriction site analysis, and the results from crossing of different strains bearing either type of X chromosome, showed that An. hermsi does not have a unique or diagnostic X chromosome. Anopheles hermsi was collected in San Mateo County, CA, which is now the northernmost known limit of this species. Crossing studies, or the examination of rDNA restriction enzyme profiles, are presently the only means of identifying An. hermsi.

Animals↗
PubMed1991

Genetic structure of natural populations of Anopheles albimanus in Colombia.

Electrophoretic and cytogenetic studies were undertaken on the population structure of Anopheles albimanus from 11 localities in Colombia, 3 from northern (Atlantic coast) and 8 from southern (Pacific coast) regions. Of the 25 allozyme loci examined, significant allele frequency differences were observed at 4 loci: hydroxy acid dehydrogenase (Had-1) and 3 esterases (Est-2, Est-4 and Est-6). The northern populations had higher variability, with 55% polymorphic loci, a mean heterozygosity of 20.4% and a mean of 3.0 alleles per locus. These values for southern populations were 24%, 9.1% and 1.5%, respectively. There were neither diagnostic loci nor clinal effect on frequencies of allozymes. Except for a small inversion on the X chromosome in low frequency in certain populations, all populations were homosequential in chromosomal banding patterns. Hybrids from matings between natural populations and the Gainesville laboratory strain were fully fertile. Estimates of genetic similarities (0.95-0.97 among southern and 0.99-1.00 among northern populations) suggest a lack of significant genetic differentiation among distant populations in this species. Based on the chromosomal, hybridization and electrophoretic data, we concluded that mosquitoes from the 11 collections were conspecific populations of An. albimanus.

Alleles↗
PubMed1990

A simple method for shipping field collected mosquitoes for electrophoretic studies.

A method for preserving field collected material in frozen condition for electrophoresis is described. A mixture of ice and salt was used to obtain a freezing temperature of -20 degrees C. Field collected mosquitoes can be stored for up to 9 or more days in an ordinary thermos bottle by replacing the ice-salt mixture at 3-day intervals, without loss of enzyme activity. This method is a considerable improvement for the shipment of material from the field to the laboratory.

Animals↗
PubMed1990

Hexane preserves biological activity of isozymes and DNA.

Live or frozen insects are required for using isozyme and DNA RFLP methods in studies on population structure, systematics and incrimination of sibling species. Difficulty in keeping insects alive or unavailability of liquid nitrogen or dry ice at regular intervals during extended collection trips poses a serious problem. We describe a method for preserving insects in hexane, under field conditions, for isozyme and DNA analysis.

Animals↗
PubMed1990

Evidence for microgeographic genetic subdivision of Anopheles quadrimaculatus species C.

Species C of the Anopheles quadrimaculatus complex has a patchy distribution and has been found principally near the coast in river and springs systems of northwest Florida (GULF, SR, SFR--designated as C1, and CHOC--designated as C2) and the Ogeechee River (OGE--C2) near Savannah, Georgia. We have documented significant differences in allelic frequencies at 5 loci (malic enzyme, aconitase, aldehyde oxidase, esterase-5 and esterase-6), and genetic substructuring (Fst) between C1 and C2. The GULF and CHOC populations occurred in apparently similar environments, but were separated by about 160 km. Both these populations are separated from OGE by over 160 km (with low to undetectable distribution of species C in the transect regions). The higher genetic similarity of the CHOC with OGE populations indicated either selective pressures or genetic drift or both as being responsible for the differences between C1 and C2 populations.

Alleles↗
PubMed1989

Dichotomous electrophoretic taxonomic key for identification of sibling species A, B, and C of the Anopheles quadrimaculatus complex (Diptera: Culicidae).

Samples of 17 populations of Anopheles quadrimaculatus Say from Florida, Alabama, Arkansas, Louisiana, Mississippi, Tennessee, New York, and New Jersey were analyzed for genetic variability at 33 enzyme loci. Statistical analysis of electromorph frequency distributions indicated that sympatric sibling (morphologically indistinguishable) species occurred in about 59% of the populations tested. The association of polytene chromosome and electrophoretic patterns of individual field-collected females confirmed species-specific diagnostic allozymes, which were useful in identifying sibling species A, B, and C and in estimating the proportions of each species at the 17 collection sites. A dichotomous electrophoretic key is presented for the identification of sibling species of the An. quadrimaculatus complex. The electrophoretic method is better than the ovarian polytene chromosome method, because mosquitoes of both sexes and females irrespective of their gonotrophic condition can be identified.

Animals↗
PubMed1989

Identification of species D, a new member of the Anopheles quadrimaculatus species complex: a biochemical key.

Sibling species D, a new member of the Anopheles quadrimaculatus species complex was identified in collections from Pickwick Lake, Tishomingo County, Mississippi and Choctawhatchee, Bay County, in West Florida. This species occurred sympatrically with the previously described species, A, B and C. Evidence for identification of species D includes diagnostic allozymes, a lack of polytene chromosomes in the ovarian nurse cells, and inviability of F1 progeny and lack of sperm transfer in hybridization crosses. An electrophoretic taxonomic key for distinguishing species D from A, B and C is presented.

Animals↗
PubMed1988

A new member of the Anopheles quadrimaculatus complex, species C.

A new member, species C, of the Anopheles quadrimaculatus complex was recently found in collections from the northwest coast of Florida. This new species cannot be differentiated from the other 2 species with available taxonomic keys. Evidence for this taxon as a sibling species includes data on hybrid sterility and distorted sex ratios in the progeny of crosses to species A and B, chromosomal differences, and diagnostic allozymes.

Animals↗
PubMed1987

Primary congenital glaucoma clinical presentation and evaluation of modified trabeculectomy.

Primary congenital glaucoma is a relatively rare condition. A study on this subject to observe the mode of clinical presentation in our country and to evaluate the role of modified technique of trabeculectomy was undertaken. 30 eyes of 17 patients having primary congenital glaucoma were studies. The examination under general anaesthesia included (a) Anterior segment examination under operating microscope, (b) Corneal diameter measurement, (c) Fundus examination (d) IOP measurement and (e) Gonioscopy. The patients were subject to modified trabeculectomy operation. The assessment of the surgery was done during post-operative examination carefully. This paper includes an analysis of various clinical features of this condition. The observations revealed that the presenting symptoms are slightly different in our country compared to those in the developed countries. The overall success rate with our modified technique of trabeculectomy was 72.4 percent. Since most of our patients present with corneal opacity, we feel that modified trabeculectomy is a very effective surgical method for such cases.

Child, Preschool↗