• V. Arunachalam

      Articles written in Journal of Genetics

    • A study of inbreeding in some models of artificial selection

      V. Arunachalam

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      An attempt is made to study the progress of inbreeding in a population by simple models of artificial selection. One or two top ranking individuals are selected based on the phenotypic value of a metric from theN progenies resulting from any particular mating (denoted as Model 1 and Model 2). The generation matrix method is employed to study the progress towards homozygosity. The probability that a selected individual is of a given genotype or that a selected pair consists of specified genotypes has been computed by numerical integration as well as by simulation, assuming the phenotypic distribution to be normal with the mean at the genotypic value and a given variance. It is observed that Model 1 promotes homozygosity more quickly than Model 2 as expected. Modifications due to dominance in the progress towards homozygosity are also discussed. The study throws some light on simulation studies in genetics.

    • Negentropy and population mean fitness in genetical systems

      V. Arunachalam

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    • Heterosis for characters governed by two genes

      V. Arunachalam

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      An expression for heterosis over midparent is derived for characters governed by one gene when hybrids are made using arbitrarily inbred parents. It is shown that, so long as inbreeding does not depress the vigour and fitness of parents, heterosis in hybrids between them will be greater than that obtained in hybrids between open-pollinated parents.

      The expression derived tor heterosis for characters governed by two genes has brought to focus the possibilities of obtaining heterosis without the presence of dominance etfects, and also of dominance interactions. Arguments are advanced to illustrate that pure dominance hypothesis alone cannot account tor the observed heterosis when the character is under the control of more than one gene. It is found feasible that pure additive gene action at individual genic level coupled with a favourable additive x additive interaction can produce heterosis when gene frequency differences can be ensured. Implications of thisresult to problems in plant breeding are discussed.

    • Extending the definition of additive genetic variance to more than one gene-a viewpoint

      V. Arunachalam

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      Following the Fisherian approach, the expression for additive genetic variance is derived in a single gene system through a regression equation in two variables which are used to obtain the additive and dominance variances. The approach is extended to two genes with restricted linkage and inbreeding. It was brought out that additive genetic variance defined essentially for one gene does not extendper se to multi-gene systems.

    • RFLP approach to breeding for quantitative traits in plants—a critique

      V. Arunachalam Shanti Chandrashekaran

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      A number of recent papers suggest that use of RFLPs as markers offers a clear advantage in breeding for improvement in quantitative traits (QTs). The concepts underlying establishment of linkage between RFLP markers and QT loci stem from three papers on tomato published during 1987–1991. Essentially, continuously varying QT phenotypes are assigned to RFLP genotype classes, which can be considered to be determined by a single, diallelic gene with codominant alleles. Linkage is inferred through statistical analysis. Similarly, interaction between markers and QT is also tested by an analysis of variance. Here, the statistical methods employed in these three papers to detect linkage are critically evaluated, especially because subsequent investigations take the concepts developed in these papers as proven. In this paper, we examine the three fundamental papersde novo. We scrutinize the methods employed and the inferences drawn to bring to light what we believe are conceptual drawbacks.

    • Marker-aided genetic divergence analysis inBrassica

      V. Arunachalam Shefali Verma V. Sujata K. V. Prabhu

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      Genetic divergence was evaluated in 31 breeding lines from fourBrassica species using Mahalanobis'D2. A new method of grouping usingD2 values was used to group the 31 lines, based on diagnostic morphological traits (called morphoqts). Isozyme variation of the individual enzymes esterase and glutamate oxaloacetate was quantified by five parameters (called isoqts) developed earlier. Grouping by the same method was also done based on the isoqts, and the grouping by isozymes was compared with that by morphoqts. Overall, there was an agreement of 73% suggesting that isoqts can be used in the choice of parents and also first stage selection of segregants in the laboratory. It was suggested that such an exercise would help to take care of season-bound and field-related problems of breeding. The new isozyme QTs, within lane variance of relative mobility and relative absorption, accounted for about 50% of the total divergence. The utility of the new method and isoqts in cost-effective breeding were highlighted.

    • Computational identification and analysis of single-nucleotide polymorphisms and insertions/deletions in expressed sequence tag data of Eucalyptus

      Tiratha Raj Singh Arun Gupta Aykkal Riju M. Mahalaxmi Abhik Seal V. Arunachalam

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