A few years ago, the genome of yeast has been fully mapped and sequenced. An interesting fact that was discovered is that almost every DNA subsequence happens to have a twin subsequence almost identical to it in the genome. This appears to be due to a doubling of the entire genome at one point during the course of evolution, and since that doubling, various genome rearrangements took place, mixing the genome into the shape we know today.
A comparison of the DNA of mice and men shows that any specific mouse chromosome contains various parts that can be found in different human chromosomes. The explanation for this is also genome rearrangements, that took place both in the mouse genome and in human genome, ever since the two split apart in the evolutionary tree, some 80 million years ago (see figure 10.7).
A comparison of human X-chromosome to cow and mouse X-chromosomes is also shown. Sites which are conserved between the species are shown (see figure 10.8). Note that since the X chromosome contains only genes that appear either once or twice in a cell, its overall content is rather conserved among mammals.
