Approximately what percentage of the human genome is identical to that of a chimpanzee?

Chimpanzees and humans share 98.8% of their genomes.

Despite this high percentage, there have been differences between the two lineages: chromosomal rearrangements, five million deletion/insertion events, and thirty-five million single-nucleotide changes have occurred between the two species (TC Sequencing et al., 2005). Human chromosome 2 is a fusion of chromosomes 2a and 2b, which remain separate in the chimpanzee lineage (TC Sequencing et al., 2005). Moreover, chimpanzees have lost three genes known to be involved in inflammation, whereas humans have lost the ability to produce a gene that may have implications for preventing Alzheimer's (TC Sequencing et al., 2005).

You may want to brush up on your knowledge of genetics if you're wondering how this is possible (why don't we act and look more like chimpanzees?). Although our genes may be similar, there are differences in the ways that these genes are expressed. For instance, approximately 29% of human and chimpanzee genes code for the same amino acids (TC Sequencing et al., 2005). Epigenetics also plays a part.

See this Smithsonian Institution link for additional information on primate genetics.

See the original academic paper on the differences between the chimpanzee and human genomes for more information in great detail.

Approximately 98.7% of the human genome is identical to that of a chimpanzee.