Because dna evolves at a relatively steady rate, gene sequences in two different organisms will accumulate sequence changes and becoming more different with time. some genes are under more selection and so evolve more slowly. other genes evolve quite quickly. assuming that sites change linearly with time, we can calculate how many sites differ when comparing genes between different species. for simplicity we’ll assume each of these genes is 1000 bp long. species compared # of sites that vary when comparing 2 sequences ribosomal rna hemoglobin mitochondrial cytochrome b human and chimp 1 14 49 human and orangutan 3 32 112 human and gibbon 4 40 140 human and macaque 6 58 203 human and mouse 18 180 630
a. why do the three genes differ in the number of variable sites between different species