A Study on Linkage between Genes for Pigmentation in various parts of the rice plant

Abstract

The most important problem in plant breeding is to determine the speed of genetic advance under selection, this was investigated by Panse, who introduced the method of genetic models which he considered with independently segregating factors. In the present investigation following the statistical approach given by him a similar study has been made of genetic models with linked factors. The effect of linkage on the speed of genetic advance and various F3- statistical propertice after making selection in F2, has been studied for models with one linked pair and with two independent pairs of linked factors. The various factors have been taken to be equal in magnitude. In one set of these models effect of linkage in coupling phase has been studied looping the magnitude of each factor fixed, while in the other set the effect of keeping the F2 genotypic variance in the start (before selection) fixed, has been studied. The various values of the recombinant fractions have been so chosen, so as to over the whole range of linkage. The various F3 statistical properties studied were- (1) the genotypic mean of F3 progeny (2) mean genotypic variance within F3 progeny (3) the variance of the genotypic mean of F3 progeny (4) the covariance of the F3 progeny mean and variance within progeny and (5) the variance of genotypic variance within F3 progeny. For the modals with a single linked pair of factors corresponding to the both sets of modals, since the number of genotypic classes was not large, the results were calculated using the direct method of the genotypic, whereas for the models involving two independent linked pairs the regression method given by Panse was adopted. For the latter type of models, the moments and product moments of the three variates. X1, F3 phenotypic value X3, genotypic variance within F3 progeny and X3, the genotypic moon F3 progeny, were obtained for each model and the regression equation of five F3 – properties on the F3 phonotypic value were calculated. These equations enable the study of the effects of various characteristics of the models on the relation between F3 parentalvalue.