In a formula derived by Hans Daetwyler (“DAT-why-ler”) and colleagues, the accuracy of disease risk predictions increases with both this quantity expressed on an entry-mean basis and training population size. Brendan Maher described the problem of some of this quantity being “missing,” which GCTA analyses were introduced in order to solve. For dichotomous traits, this quantity may be estimated with ACE and other liability threshold models. Response is the product of a form of this quantity and the selection differential. One kind of this quantity excludes (10[1])variance due to dominant (10[1])and epistatic factors, while (10[2])the other (10[1])is the result of dividing genetic variance by total variance. (10[1])Those narrow-sense and broad-sense (10[2])forms (10[2])of this (10[1])quantity (10[1])are often estimated from now-widely-criticized twin studies. For 10 points, (10[1])name this parameter (10[2])that represents the variability (-5[1])in a trait due to genetics, not environmental factors or chance. (10[2])■END■