Comparative X and Y map. Sequenced X Chromosomes from nine mammals, plus available Y Chromosomes, aligned to our pig X and Y assemblies. In each dotplot, the pig chromosome is on the horizontal axis, and the subject chromosome is on the vertical axis. The cattle X sequence is plotted in reverse orientation. High-stringency alignments are shown in blue with less stringent alignments in yellow. Human, chimpanzee, cat, and dog retain the ancestral X arrangement. Sheep and cattle show a small number of rearrangements, while rodents and rabbit have a greater rate of chromosomal change. Chromosomes derived from shotgun assemblies are more prone to showing rearrangement and reflect the need for continuous assembly improvement. The Y alignments show highly variable organization, and different ancestral genes have amplified in different lineages (note that the sizes of the Y assemblies are not to scale here; see Supplemental Fig. S8 for larger versions).
