• Swastika Negi

      Articles written in Journal of Genetics

    • Estimates of covariances between Full Sibs and between Half Sibs for bristle number and wing length in samples of drosophila bred to varying levels of inbreeding

      G. C. Taneja Swastika Negi

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      Covariances between full sibs and between half sibs were estimated for bristle number and wing length in different samples ofDrosophila melanogaster bred to varying levels of inbreeding. The estimates for bristle number increased linearly with increase inF values, but for wing length the trend appeared curvilinear with concavity towards the axis representingF values.

      Mean chaeta number was not affected by the level of inbreeding, although there was an apparent trend in the reduction of wing length. Inbreeding depression measured by the number of flies which survived in each line was very apparent.

      Non-additive genetic variance was found to be unimportant in these data.

      The phenotypic variance, on the average, tended to decrease slightly with increase in inbreeding.

    • Interaction between genotype and temperature for wing length, bristle number and EGG count inDrosophila ananassae

      G. C. Taneja Swastika Negi

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      Data on wing length, bristle number and egg count were collected on two groups of full-sibs ofDrosophila ananassae, separated and raised at temperatures of 20° and 25°C from larval to adult stage. The flies raised at 20°C had longer wings and fewer bristles than those raised at 25°C. The number of eggs laid was also reduced at 20°C.

      If the effect of change of temperature from 25° to 20°C on the level of production is considered, it is more marked on the high level groups of egg count and bristle number and low level group of wing length.

      Analyses of data showed significant differences between temperatures for all the three characters. The differences between genotypes were significant for bristle number and wing length only. The genotype-temperature interactions were significant for all the three characters except for the bristle number in the female.

      Genotype-temperature interactions have been expressed as intra-class correlations to determine their relative importance. It was concluded that these interactions were more important for egg count and wing length and relatively less important for bristle number.

    • Phenotypic, genetic and environmental correlations between chaeta number and wing length inDrosophila melanogaster

      G. C. Taneja Swastika Negi Satish Kumar

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      Biometric data on bristle numbers for two segments and wing length of 936 femaleDrosophila melanogaster derived from a wild stock are presented. Heritabilities were about 0.4. The genetic correlation between the two bristle numbers was +.91, the environmental correlation insignificant. The genetic correlations between wing length and the bristle numbers were +39 and +.17, the environmental correlations again insignificant.

    • Analysis of 6 × 6 diallel cross for EGG production inDrosophila melanogaster

      H. P. Singh S. S. Prabhu Prem Narain Swastika Negi

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      There is a considerable amount of interaction between the environment and the genetic factors controlling egg production InDrosophila melanogaster.

      The genes affecting egg production exhibit both additive genetic effects and dominant deviations. They also show non-allelic interactions. The non-allelic interaction between G and D results in low egg production.

      An asymmetry in the distribution of positive and negative allels exists in the parents, which was understandable as three of the six lines included in the trial were selected for low egg production and the other three for high egg production.

      There are probably present more dominant than recessive genes affecting egg Production in the parental stock used in these studies; the ratio of recessives to dominants being of the order of 1:4. Low egg production is due to recessive genes, high egg production to their dominant allels.

      Dominance deviations present were largely unidirectional.

      The order of dominance of the six lines used was D, B, E, C, A, F.

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