Polymorphic genes in wild isolates of Caenorhabditis elegans . (A) Number of polymorphic genes per strain. Bars above zero indicate the polymorphic genes with a positive ratio (higher intensity than the mean), while bars below zero indicate the polymorphic genes with a negative ratio. The wide part of the bars refers to the genes with a ratio of greater than 1 or less than −1, while the narrow part of the bars indicates genes with a ratio of greater than 0.5 or less than −0.5. Orsay strains are shown in orange, Santeuil strains in green, and the out-group strains in purple. (B) Frequency of occurrence of polymorphic genes. Number of strains is indicated on the left, and the percentage of total is shown on the right; for example, polymorphic genes only found in one strain make up 33.2% of the total number of polymorphic genes. (C) Distribution of the polymorphic genes in 48 different C. elegans strains. Genomic position is shown on the x-axis, and the number of polymorphic genes is shown on the y-axis. Chromosomes are shown in different panels, and chromosome names are given on the left in the gray boxes. The black bars indicate the total number of polymorphic genes per 100 kb. The lines show the number of genes with a ratio of less than −0.5 for three different groups of C. elegans strains, Orsay strains are shown in orange, Santeuil strains in green, and the out-group strains in purple; for example, the large number of polymorphic genes at the beginning (left arm) of chromosome II is mostly caused by the many genes that are very polymorphic in or absent from the out-group lines (purple line is high).