2. 18. Willensdorfer M, R Burger (2003). The two-locus model of Gaussian stabilizing selection. Theor Popul Biol 64: 101-117. 2004 19. Barton NH, M Turelli (2004). Effects of genetic drift on variance components under a general model of epistasis. Evolution 58: 2111-2132. 20. Boots M, PJ Hudson, A Sasa