Genomic function (communication arising): Rate of evolution and gene dispensability

Whether more dispensable genes evolve faster than less dispensable ones is a contentious issue. Comparing yeast and worm genes, Hirsh and Fraser observe a gradual tendency for less dispensable genes (those that reduce the growth rate of yeast when knocked out) to have lower rates of protein evolution. Here we repeat their analysis using larger data sets and find no evidence that dispensability explains the variation in rates of protein evolution. Although Hirsh and Fraser provide a model to show why their result is to be expected, our analysis suggests that their model, which assumes among other things that no substitution is advantageous, cannot be generally applied.