THE ACCURACY OF PROGENY TESTING WITH BINOMIAL AUXILIARY TRAITS

The accuracy of progeny testing for a continuous trait when the auxili ary information was based on 'all-or-none' type of traits with a multi -factorial threshold model was examined. The accuracy of the progeny t est was found always to increase with the inclusion of the auxiliary t rait. It followed the same pattern as in the case of continuous auxili ary trait. However, there was an additional feature in that the accura cy was also dependent on the probability of incidence of the discrete trait unless either the progeny group size was very large, and/or ther e was no genetic correlation or else the probability of incidence was itself extremely low. Compared with the case when the auxiliary trait was continuous, there was a loss in accuracy which can be looked upon in two ways. First, the continuous auxiliary trait is itself made 'all -or-none' type by a threshold and the accuracies compared in the two c ases. The loss increases symmetrically in either direction with increa se in positive or negative directions of the difference in genotypic a nd phenotypic correlations. Secondly, a comparison can be made of the accuracy when the auxiliary trait is normally distributed with that wh en it is binomially distributed but with the same amount of genetic in formation on the observed scale as given by the heritabilities and gen etic correlations. No loss now occurs if the two classes of the binomi al trait are equally likely and the loss in accuracy increases with th e decrease in the standard deviation of the binomial distribution for given values of other parameters. It was found also that the use of bi nomial auxiliary trait reduced the number of progeny required to attai n a pre-assigned level of accuracy, resulting in a decreased cost of t he programme compared with that when no binomial auxiliary trait was u sed.