▁to ▁produce ▁try pt oph an . ▁He ▁found ▁that ▁when ▁ye ast ▁colon ies ▁were ▁moved ▁from ▁a ▁try pt oph an - rich ▁medium ▁to ▁a ▁minimal ▁one , ▁revert ants ▁continued ▁to ▁appear ▁for ▁several ▁days . ▁The ▁degree ▁to ▁which ▁revert ants ▁were ▁observed ▁in ▁ye ast ▁was ▁not ▁as ▁high ▁as ▁with ▁b acter ia . ▁Other ▁scient ists ▁have ▁conducted ▁similar ▁experiments , ▁such ▁as ▁Hall ▁who ▁tested ▁hist id ine ▁revert ants , ▁or ▁Ste ele ▁& ▁J inks - Ro bert son ▁who ▁tested ▁l ys ine . ▁ ▁These ▁experiments ▁demonstrate ▁how ▁recom bin ation ▁and ▁DNA ▁rep lication ▁are ▁necessary ▁for ▁adapt ive ▁mut ation . ▁However , ▁in ▁l ys ine - test ed ▁cells , ▁recom bin ation ▁continued ▁to ▁occur ▁even ▁without ▁selection ▁for ▁it . ▁Ste ele ▁and ▁J inks - Ro bert son ▁concluded ▁that ▁recom bin ation ▁occurred ▁in ▁all ▁circumstances , ▁adapt ive ▁or ▁otherwise , ▁while ▁mut ations ▁were ▁present ▁only ▁when ▁they ▁were ▁benef icial ▁and ▁adapt ive . ▁ ▁Although ▁the ▁production ▁of ▁mut ations ▁during ▁selection ▁was ▁not ▁as ▁vig orous ▁as ▁observed ▁with ▁b acter ia , ▁these ▁studies ▁are ▁convin cing . ▁As ▁mentioned ▁above , ▁a ▁subsequent ▁study ▁adds ▁even ▁more ▁weight ▁to ▁the ▁results ▁with ▁l ys 2 . ▁Ste ele ▁& ▁J inks - Ro bert son ▁ ▁found ▁that ▁L YS ▁pro tot roph s ▁due ▁to ▁inter chrom os om al ▁recom bin ation ▁events