“…On the other hand, association studies tend to involve more than one quantitative traits or complex diseases located in different regions of chromosomes, allowing the investigation of common genetic risk factors underlying multiple traits. Although these traits could be analyzed separately with univariate genetic model, statistical methods and algorithms have been developed for simultaneously analyzing multiple normal traits (Jiang and Zeng, 1995;Fang et al, 2008;Ayroles et al, 2009;Zhu and Zhang, 2009;Stephens, 2010;Nadeau and Dudley, 2011;Shriner, 2012), multiple discrete traits (Lange and Whittaker, 2001;Xu et al, 2005;Yang et al, 2009) and multiple mixed traits of normal and discrete traits (Prentice and Zhao, 1991;Fitzmaurice and Laird, 1997;Liu et al, 2009).…”