Human 5q22.2 and 18q21.1-21.2 are evolutionarily unstable. A: Human 5q22.2 (112-113 Mb) is shown as the bar with its gene-coding regions (APC, MCC, etc.) shaded. When compared to species above (horse, rhesus, orangutan and chimp; with the orthologous chromosome of the human chromosome 5 represented by the number inside the bar), no rearrangements were found. However, when compared to species below (rat, mouse, pig, dog, cow, opossum, and platypus) or nearby (chicken and lizard), rearrangements were identified within the region. Rearrangement breakpoints are indicated by gaps between the bars, with numbers inside each bar representing the Mb region of a chromosome (e.g., "18, 25.2-26.8" represents 25.2-26.8 Mb of chromosome 18) or a supercontig/ultra-contig/scaffold (e.g., S1,0-3.4). "Un" stands for chromosome "Unknown" in the released genome assembly. The arrow of each bar designates the sequence direction, and a dished arrow indicates that the homology to the human extends beyond 5q22.2 shown here. B: Human 18q21.1-q21.2 (43-50 Mb) encodes three SMAD genes, two MBD genes, DCC, and a number of other genes (not shown). The same as above, no rearrangements were found when compared to species shown above the human. However, when compared to the species shown below, rearrangements were found within the region and/or nearby. In addition, many sequences are missing in the orthologous chicken and lizard sites (demonstrated by large gaps in the alignment). The question mark "?" inside or below the cow bars indicates that the human-cow alignment at this region has not been completely resolved.