Large-scale mutations. (a) Mutations that lead to alterations in a chromosome can occur internally through deletion, duplication, or inversion events (top), or they can be due to an insertion (middle) or translocation (bottom), exchanging DNA with another chromosome. (b) Simians such as chimpanzees have a genome consisting of 25 different chromosomes, rather than the 24 different chromosomes (22 autosomes plus the sex chromosomes X and Y) found in humans. The distinction is not as great as it sounds. Two simian chromosomes were fused during the evolution of hominids, producing human chromosome 2—shown next to the related chromosomes from (left to right) chimpanzee, gorilla, and orangutan.