Mammalian genomes ease location of human DNA functional segments but not their description

Under the assumption that a significant motivation for sequencing the genomes of mammals is the resulting ability to help us locate and characterize functional DNA segments shared with humans, we have developed a statistical analysis to quantify the expected advantage. Examining uncertainty in terms of the width of a confidence interval, we show that uncertainty in the rate of nucleotide mutation can be shrunk by a factor of nearly four when nine mammals; human, chimpanzee, baboon, cat, dog, cow, pig, rat, mouse; are used instead of just two; human and mouse. Contrastingly, we show confidence interval shrinkage by a factor of only 1.5 for measurements of the distribution of nucleotides at an aligned sequence site. These additional genomes should greatly help in identifying conserved DNA sites, but would be much less effective at precisely describing the expected pattern of nucleotides at those sites.