▁adapt ive ▁mut ation ▁was ▁not ▁at ▁work ▁because ▁natural ▁selection ▁would ▁not ▁favor ▁this ▁mut ation ▁in ▁the ▁new ▁environment . ▁ ▁Although ▁there ▁are ▁many ▁gen es ▁involved ▁in ▁adapt ive ▁mut ation , ▁Rec G , ▁a ▁protein , ▁was ▁found ▁to ▁have ▁an ▁effect ▁on ▁adapt ive ▁mut ation . ▁By ▁itself , ▁Rec G ▁was ▁found ▁to ▁not ▁necessarily ▁lead ▁to ▁a ▁mut ational ▁phen ot ype . ▁However , ▁it ▁was ▁found ▁to ▁in hib it ▁the ▁appearance ▁of ▁revert ants ▁( cell s ▁that ▁appeared ▁normally , ▁as ▁opposed ▁to ▁those ▁with ▁the ▁mut ations ▁being ▁studied ) ▁in ▁wild - type ▁cells . ▁On ▁the ▁other ▁hand , ▁Rec G ▁mut ants ▁were ▁key ▁to ▁the ▁expression ▁of ▁Rec A - dependent ▁mut ations , ▁which ▁were ▁a ▁major ▁portion ▁of ▁study ▁in ▁the ▁S OS ▁response ▁experiments , ▁such ▁as ▁the ▁ability ▁to ▁util ize ▁la ct ose . ▁ ▁Ye ast ▁Dr . ▁von ▁Bor st el , ▁in ▁the ▁ 1 9 7 0 s , ▁conducted ▁experiments ▁similar ▁to ▁the ▁L act ose ▁Star v ation ▁experiment ▁with ▁ye ast , ▁specifically ▁Sac char omy ces ▁c ere vis iae . ▁He ▁tested ▁for ▁try pt oph an ▁aux ot roph ▁revert ants . ▁A ▁try pt oph an ▁aux ot roph ▁cannot ▁make ▁try pt oph an ▁for ▁itself , ▁but ▁wild - type ▁cells ▁can ▁and ▁so ▁a ▁revert ant ▁will ▁revert ▁to ▁the ▁normal ▁state ▁of ▁being ▁able