Re: How is the genetic diference between two closly related species evaluate

There are several basic observations that allow the estimate of a 1.5 % genetic difference between humans and chimpanzees:

1. DNA hybridization studies- when DNA from chimpanzees is denatured (i.e., the DNA strands separated) and allow to reform double stranded DNA molecules in the presence of human DNA, the majority of chimp DNA is able to form "hybrid" DNA molecules with human DNA.

2.chromosome banding patterns- humans have 46 chromosomes (23 pairs) while chimps have 48 (24 pairs). Isolated chromosomes from chimps and humans show similar "bands" or staining patterns and the difference in the the number and staining patterns can be explained by chromosome fusion and rearrangement (http://www.amnh.org/enews/headl/e1_h6.html) Visit this site for a good picture of human/chimp chromosome banding.

3. Comparison of DNA sequences from already sequenced human/chimp genes.Although not all DNA/genes have been sequenced from these two related species, one can estimate the overall divergence between the genomes using the DNA sequences that are already known.