Chromosomal repatterning in drosophila: Drosophila nasuta nasuta and D. kohkoa

Two three-break shifts (transpositions) are detected in a chromosome comparison between D.n. nasuta and D. kohkoa. Such aberrations are not reported in studies with chromosome comparisons in Drosophila species. The probable sequences are given to explain the occurrence of these transpositions

Toxicity and the effect of Zineb on the rate of development of Drosophila melanogaster

Zineb, (zinc ethylene bis (dithiocarbamate), a carbamate fungicide was analysed for its toxicity on Drosophila meanogaster . Different concentrations of the chemical were added to the food medium and fed to the larvae. Based on this, the LC50 was calculated to be 58·26 mg/100 ml food medium. The toxic efficacy, of Zineb on the rate of development and viability of D. melanogaster compared to Dithan M-45, a related carbamate, are discussed

Population genetics of Drosophila nasuta nasuta, Drosophila nasuta albomicana and their hybrids. I. Karyotypic mosaicism in the hybrid populations

D. n. nasuta and D. n. albomicana constitute a pair of chromosomal races with 2n=8 and 2n=6, respectively. The F1 of these has 2n=7 and it is fertile. There exists a state of karyotypic mosaicism as evidenced by the presence of 26 types of chromosome combinations in F2, F3 and F10 populations. In the midst of this karyotypic noise, the karyotype similar to that of F1 reached 51% of the population. Implications of these findings are discussed

Chromosomal dynamics of Gastrimargus

Chromosome number and morphology have been regarded as most constant properties of a species both within and between different individuals. This is also, true of short-horned grasshoppers The concept of absolute karyotypic stability entails an evolutionary cul-de-sac, and therefore a relative stability alone can afford scope for further genotypic change. Though it is known that spontaneous chromosomal mutations in stable genetic systems is low, yet chromosomal variations within an organism is as common as between organisms within a population. However, a re-organization of a karyotype to attain a better homeostatic stability depends not only on the incidence of structural and numerical anomalies but also on their subsequent survival. Such selective incorporation of anomalies are claimed in orthopterans. The incorporation of anomalies into a genetic system is as much a measure of karyotypic plasticity as it affords the starting point of further evolutionary change. Cytological examination of the two species of Gastrimargus, G. transversus and G. africanus orientalis (Family, Acrididae; Order, Orthoptera) collected locally (Mysore, India) has clearly shown the karyotypic dynamism

Meiosis in the male Periplaneta americana

Cytology of the common cockroach Periplaneta americana (Blattidae) dates back to 1909, and yet recent re-examination has not only brought to light interesting details, but also much controversy. It was therefore felt necessary to examine the locally available species of cockroaches with the view of understanding the intricacies of the problem. Absence of diplotene-diakinesis and chiasmata in meiosis in the male has been claimed and various explanations have been marshalled. But Lewis and John, taking into consideration all the aspects of indirect evidence, state that chiasmata might occur at the terminal ends of chromosomes and might terminalize rapidly

Studies on isozyme variations in a few members of Drosophila nasuta subgroup

Isozyme variation at six enzyme loci has been studied involving nine members of Drosophila nasuta subgroup, by employing polyacrylamide gel electrophoretic technique. Alleles at three loci namely Acph, Aph and α-Est are found to be highly polymorphic; whereas at β-Est locus the alleles are less variable while at α-Gpdh and To loci, the alleles are found to be least variable. Null alleles are encountered in low frequencies at α-Est, β-Est and c-Gpdh enzyme loci. The allelic frequencies obtained at the six enzyme loci have been utilised as a yardstick to measure the extent of genetic relationship between the species studied. The genetic identity and genetic distance between these closely-related species have been estimated by adopting the Nei's formula. These findings have been discussed with reference to earlier cytogenetic and hybridisation studies made on this subgroup

C-banding in male meiotic chromosomes of Poekilocerus pictus (Acrididae: Orthoptera)

Studies on the C-heterochromatin during the meiosis in the Indian grasshopper Poekilocerus pictus has been carried out using the BSG technique presumably for the first time. It is shown that the genome of this grasshopper is endowed with large amounts of repetitive DNA in the centromeric, interstitial and telomeric regions. This Acridid under study differs in having distinct centromeric, interstitial and telomeric blocks in majority of the chromosomes from the British Acridid Myrmeleotettix maculatus which has interstitial bands only in the X-chromosome and the B-chromosome but not in the autosomes