Fig. 1

Crossing scheme used to make the four parental mpRIL population. Different populations of worms are shown in the colored circles. Magenta solid lines indicate the hermaphrodite parental lines, and the dashed blue lines show the male parental lines. A JU1511 hermaphrodite (yellow) was crossed with a JU1926 male (red) to create F1 population W. A JU1941 hermaphrodite (blue) was crossed with a JU1931 male (green) to create F1 population X. Individuals from populations W and X were reciprocally crossed to create seven separate populations. In this way, we obtained different populations of genotypes with mixed genetic background from the four parental lines. Individuals from the seven separate populations (A, B, Y1, Y2, Z, C, and D) where further intercrossed to obtain extra recombinations mainly to break up the X-chromosome, which lacks recombination in the male. These populations are labeled E to Q. From these populations (light blue), individuals were taken for inbreeding via self-fertilization for six generations to create mpRILs. For details, see also Additional file 1: Table S1 and Fig. 3