Pictorial comparison of human and ape chromosomes

The closest relatives that humans have in the animal world are the great apes. Of the apes, our very closest relatives are the chimpanzees. This pictorial guide to the chromosomal banding patterns of humans and apes provides clear and convincing evidence of that relationship. For each of the chromosomes, the human is on the left, then the chimpanzee, then the gorilla, and finally the orangutan, a distant relative. Notice the similarity between humans and chimpanzees - in fact, human chromosome #2 is thought to have resulted from a fusion of chimp chromosomes. Human chromosome #2 has an inactive centromere exactly where the active chimp centromere is positioned, and at the human centromere, DNA sequencing has shown the order pre-telomere, telomere, telomere, pre-telomere; exactly what would be predicted by a head to head fusion of two chromosomes into one. This reduction from 24 pairs of chromosomes in chimps to 23 pairs in humans could help explain the origin of reproductive isolation between humans and chimps - possibly leading to a form of reduced hybrid viability, as sperm and egg fail to fuse after fertilization due to unequal haploid number. Thanks to Dr. Beth Kramer and Indiana University for this reproduction from the original article in Science magazine.