If genetic and environmental effects upon a quantitative phenotype X=G+E are normally and independently distributed then the probability distribution of genetic value G among individuals of fixed phenotypic value X is likewise a normal distribution. The mean of this a posteriori distribution of genetic values is \(\bar g\)+h2 (X−\(\bar g\)) and the variance is σg2(1−h2), where \(\bar g\) is the a priori mean of X, h2 is the heritability ratio, and σg2is genetic variance. For any fixed values of h2 and σg2the a posteriori probability that the genetic value G associated with a given phenotype X exceeds the population mean by any specified amount can therefore be read directly from the tables of the standard normal distribution. The expected proportion of these superior genetic deviates among individuals whose phenotypic value exceeds some specified constant may also be calculated (by numerical analysis) and is presented here in graphical form.