Proportions of male-biased and non-male-biased (female-biased and unbiased combined) genes originating in different evolutionary periods. For male-biased genes, we calculated the proportion as the number of male-biased genes in a given chromosome out of the whole genome. Analogously, we calculated non-male-biased gene proportions. Pie plots mark chromosomal proportions of male-biased genes. We pooled branches 5 and 6, considering individual small sample size. The black dashed line indicates the genomic proportion of all X-linked genes, 0.16. We used the exponential decay formula, f(t) = N[ert(1 − d) + d], to model the origination process of male-biased genes, which converged as: N = 1.14, r = 0.07, and d = 0.09.
