How closely related are mice and humans? How many genes are the same?
Answer provided by Lisa Stubbs of Lawrence Livermore National Laboratory, Livermore, California. Mice and humans (indeed, most or all mammals including dogs, cats, rabbits, monkeys, and apes) have roughly the same number of nucleotides in their genomes — about 3 billion base pairs. This comparable DNA content implies that all mammals contain more or less the same number of genes, and indeed our work and the work of many others have provided evidence to confirm that notion. I know of only a few cases in which no mouse counterpart can be found for a particular human gene, and for the most part we see essentially a one-to-one correspondence between genes in the two species. The exceptions generally appear to be of a particular type –genes that arise when an existing sequence is duplicated. Gene duplication occurs frequently in complex genomes; sometimes the duplicated copies degenerate to the point where they no longer are capable of encoding a protein. However, many duplicated genes re