Gene. 2005 Feb 14;346:215-9.

Eighty percent of proteins are different between humans and chimpanzees.

Glazko G, Veeramachaneni V, Nei M, Makalowski W.

Institute of Molecular Evolutionary Genetics, Pennsylvania State University,
University Park, PA 16802, USA.

The chimpanzee is our closest living relative. The morphological differences
between the two species are so large that there is no problem in distinguishing
between them. However, the nucleotide difference between the two species is
surprisingly small. The early genome comparison by DNA hybridization techniques
suggested a nucleotide difference of 1-2%. Recently, direct nucleotide
sequencing confirmed this estimate. These findings generated the common belief
that the human is extremely close to the chimpanzee at the genetic level.
However, if one looks at proteins, which are mainly responsible for phenotypic
differences, the picture is quite different, and about 80% of proteins are
different between the two species. Still, the number of proteins responsible
for the phenotypic differences may be smaller since not all genes are directly
responsible for phenotypic characters.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15716009&query_hl=1

Tom Billings