• M R Rajasekarasetty

      Articles written in Proceedings – Animal Sciences

    • The annual reproductive behaviour of the green frog,Rana hexadactyla Lesson, in and around Mangalore and Mysore city (India)

      M Gopalakrishnan M R Rajasekarasetty

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      The annual reproductive behaviour of the frog,Rana hexadactyla, was studied from two climatologically contrasting regions and correlated with the environmental conditions, like temperature, relative humidity and rainfall prevailing there. Since some data were available on the gonadal activity of this species from two other areas, they were also considered. The results show that the gametogenic activity is under the marked influence of the range of temperature and relative humidity prevailing in the locality while the pattern of rainfall plays a supplementary role. The activity begins sometime in March or April when the locality experiences the pre-monsoon (south west) showers. The gametogenesis occurs rapidly around Mangalore where the range of temperature between the monthly mean maximum and the minimum is narrow and stable from April to October but in Mysore city similar environmental conditions are seen from June to October and the gametogenesis becomes active during this period. Thus, ovulation and oviposition take place during June or July at Mangalore whereas the same occur towards the end of August at Mysore city.

    • Population genetics ofDrosophila nasuta nasuta, Drosophila nasuta albomicana and their hybrids II. Coassociation of parental chromosomes in the hybrid populations

      M R Rajasekarasetty N B Krishnamurthy H A Ranganath

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      D. n. nasuta (2n=8) andD. n. albomicana (2n=6), the chromosomal races of thenasuta subgroup have mutual open genetic systems. Hybrid populations are completely fertile. By utilising fixed inversion differences in second and third chromosomes, the extent of coassociation of parental chromosomes in the gene pool of the hybrids have been estimated. There is a significant decline in the Inversion polymorphism of the second chromosome, while in the third chromosome both the parental and the hybrid associations are equally frequent. The reduction in the frequency of heterokaryotypes in the second chromosome is due to the establishment of different coadapted systems in the parental chromosomes which has been favoured by selection. This does not occur in the third chromosome. This dochotomy of differential coadaptation within the elements of the same genotype is the first of its kind and the implications of these findings are discussed.

    • Chromosome biology of the scorpionPalamnaeus sp

      M R Rajasekarasetty N V Aswathanarayana K R Kumaraswamy

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      The chromosomes of the male scorpionPalamnaeus sp. has been analysed making use of the Colchicine-hypotonic-suspension technique. The diploid number has been found to be 62. The presence of clear constrictions on the spermatogonial metaphase chromosomes is noticed. The occurrence of diplotene-diakinesis, chiasmata and translocations have been encountered. The nature of the kinetochore is discussed. It is opined that the chromosomes of this scorpion are apparently monocentric (represented by constrictions on chromosomes) but behaving as holocentric.

    • Numerical variations of chromosomes in the natural populations of Indian acridids

      M Edward Gururaj M R Rajasekarasetty

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      Nine natural populations of Indian acridids belonging to seven species were cytologically analysed to study the numerical variations of chromosomes in the male germline cells. Of these, two allopatric populations ofA. humbertianus and two ofO. nitidula were chosen for intraspecies interpopulational studies. Both aneuploidy and polyploidy were encountered as intraindividual variations. Two kinds of polyploid cells—one with and another without multivalents—were found to occur. The former signified the occurrence of premeiotic mitotic breakdown of spindle whereas the latter was due to the failure of cytokinesis. While many tetraploid cells without multivalents successfully consummated meiosis producing dimegalous spermatids, tetraploid cells with multivalents and higher polyploids degenerated without completing meiosis. Analysis of quantitative data indicated that failure of cytokinesis is more frequent than spindle in premeiotic mitotic divisions. The frequency of second meiotic polyploid cells was significantly higher than those of first meiosis. The probable reasons for the increased incidence have been discussed. Comparative analysis of qualitative and quantitative data of these anomalies for the allopatric populations ofA. humbertianus andO. nitidula showed that the population structure and breeding systems have an impact on the origin and incidence of the numerical chromosomal variations.

    • Studies on isozyme variations in a few members ofDrosophila nasuta subgroup

      S R Ramesh M R Rajasekarasetty

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      Isozyme variation at six enzyme loci has been studied involving nine members ofDrosophila 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 α-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.

    • Studies on the ontogenetic changes in the isozymes inDrosophila nasuta nasuta andDrosophila sulfurigaster neonasuta

      M R Rajasekarasetty L Siddaveere Gowda N B Krishnamurthy H A Ranganath

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      Ontogenetic manifestations of four isozymes namely, acid phosphatase, alkaline phosphatase, α-esterase and β-esterase have been analysed in two closely related species—D. nasuta nasuta andD. sulfurigaster neonasuta. By adopting polyacrylamide gel electrophoretic technique 15 different developmental stages have been assayed. Electrophoretically homologous and distinct enzyme phenotypes for each enzyme system have been recognised in the two species under study. The implications of these findings are discussed.

    • Chromosomal repatterning in drosophila:Drosophila nasuta nasuta andD. kohkoa

      S R Ramesh M R Rajasekarasetty

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

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