The large X-effect on secondary sexual characters and the genetics of variation in sex comb tooth number in .

Genetic studies of secondary sexual traits provide insights into whether and how selection drove their divergence among populations, and these studies often focus on the fraction of variation attributable to genes on the X-chromosome. However, such studies may sometimes misinterpret the amount of variation attributable to the X-chromosome if using only simple reciprocal F crosses, or they may presume sexual selection has affected the observed phenotypic variation. We examined the genetics of a secondary sexual trait, male sex comb size, in .