I keep hearing this claim that a lab "rat has 99% of the DNA of a human?" Is that so? What exactly does this mean? One source for this claim seems to CNN which only says,
"About 99 percent of genes in humans have counterparts in the mouse," said Eric Lander, Director of the Whitehead Institute Center for Genomic Research in Cambridge, Massachusetts. "Eighty percent have identical, one-to-one counterparts."
It further says,
Mice and humans each have about 30,000 genes, yet only 300 are unique to either organism. Both even have genes for a tail, even though it's not "switched on" in humans.
This article says we only share 96% with chimps!
Another implication of the finding is that we are more different to our closest living relative, the chimpanzee, than previously assumed from earlier studies. Instead of being 99 per cent similar, we are more likely to be about 96 per cent similar.
While not 99% as the original claim, here is a source along the same lines at 97.5% of their (working) DNA of humans.
Mice and men share about 97.5 per cent of their working DNA, just one per cent less than chimps and humans. The new estimate is based on the comparison of mouse chromosome 16 with human DNA.