▁in ▁bio in format ics ▁ ▁Det erm ining ▁the ▁time ▁of ▁diver gence ▁in ▁ph y log en etic ▁trees ▁The ▁mole cular ▁clock ▁hypothesis ▁predict s ▁that ▁the ▁rate ▁of ▁am ino ▁acid ▁substitution ▁in ▁a ▁particular ▁protein ▁will ▁be ▁approximately ▁constant ▁over ▁time , ▁though ▁this ▁rate ▁may ▁vary ▁between ▁protein ▁families . ▁This ▁suggests ▁that ▁the ▁number ▁of ▁mut ations ▁per ▁am ino ▁acid ▁in ▁a ▁protein ▁increases ▁approximately ▁linear ly ▁with ▁time . ▁ ▁Det erm ining ▁the ▁time ▁at ▁which ▁two ▁prote ins ▁diver ged ▁is ▁an ▁important ▁task ▁in ▁ph y log en et ics . ▁F oss il ▁records ▁are ▁often ▁used ▁to ▁establish ▁the ▁position ▁of ▁events ▁on ▁the ▁tim eline ▁of ▁the ▁Earth ' s ▁evolution ary ▁history , ▁but ▁the ▁application ▁of ▁this ▁source ▁is ▁limited . ▁However , ▁if ▁the ▁rate ▁at ▁which ▁the ▁mole cular ▁clock ▁of ▁protein ▁family ▁t icks ▁— ▁that ▁is , ▁the ▁rate ▁at ▁which ▁the ▁number ▁of ▁mut ations ▁per ▁am ino ▁acid ▁increases ▁— ▁is ▁known , ▁then ▁knowing ▁this ▁number ▁of ▁mut ations ▁would ▁allow ▁the ▁date ▁of ▁diver gence ▁to ▁be ▁found . ▁ ▁Suppose ▁the ▁date ▁of ▁diver gence ▁for ▁two ▁related ▁prote ins , ▁taken ▁from ▁organ isms ▁living ▁today , ▁is ▁sought . ▁The ▁two ▁prote ins ▁have ▁both ▁been ▁accum ulating ▁accepted ▁mut ations ▁since ▁the ▁date ▁of ▁diver gence , ▁and ▁so ▁the ▁total ▁number ▁of ▁mut ations ▁per ▁am ino ▁acid ▁separ ating ▁them ▁is ▁approximately