This 75.8% of the human genome is 1.23% different from the chimpanzee genome in single-nucleotide polymorphisms (SNPs - changes of single DNA “letters” in the genome). Another type of difference, called 'indels' (insertions/deletions) account for another ~3% difference between the alignable sequences. In addition, variation in copy number of large segments (> 20 kb) of similar DNA sequence provides a further 2.7% difference between the two species. Hence the total similarity of the genomes could be as low as about 70%.