Differences in variation of phenotypic trait expression between the heterogametic and the homogametic sex and its genetic basis

Differences in variation of phenotypic trait expression between males and females have been observed in multiple studies that are limited to one species, but meta-analytic evidence has failed to show consistent differences between the sexes across species. In this study, a re-analysis of meta-analytic evidence was done to focus on differences between the heterogametic and the homogametic sex rather than between males and females. A literature investigation was done to understand the evidence supporting higher variation in trait expression in the heterogametic sex, the genetic underpinning related to these differences, and how these genetic underpinnings are involved in mechanisms related to creating comparatively higher trait expression variation in one sex. The scientific literature indicates that males are more variable than females when males are heterogametic, and that females are more variable than males when females are heterogametic. Further, that higher variation in the heterogametic sex is a result of polymorphic organization of heterochromatin in the Y- or W-chromosome. Hypotheses that were suitable for meta-analytic testing were formed based on the literature. Results from the meta-analysis agrees with the findings in the literature, which was that the heterogametic sex is more variable than the homogametic, that mean male trait expression is higher than mean female trait expression, that differences in variation is higher in traits more closely related to fitness, and that differences in variation and heterogametic heritability both correlates with sex chromosome heteromorphy. Finally, potential consequences related to evolutionary dynamics were discussed.