Figure 1.

Crossing design and genotypes of experimental males. (A) The domesticus^LEWES Y chromosome (white) was introgressed onto a musculus^PWK background (black) by backcrossing hybrid males to musculus^PWK females for 11 generations. Only generations for which male reproductive phenotypes were measured are shown. Expected autosomal heterozygosity is reduced by 50% each generation. (B) Tenth generation backcross males (N₁₀ Y^LEWES) were crossed to either pure musculus^PWK females or females with domesticus^LEWES introgressions on the central (musculus^{DOM X-8}) or distal (musculus^{DOM X-9}) part of the X chromosome. Control males were generated by crossing N₁₀ females to musculus^PWK males. Sample sizes (n) are the number of males in each generation for which reproductive phenotypes were measured.