ually ▁and ▁quant it atively ▁ass essed ▁by ▁their ▁expression . ▁▁ ▁Ant ib i otic ▁resistance ▁gene : ▁similar ▁to ▁flu ores cent ▁markers , ▁ant ib i otic ▁resistance ▁gen es ▁are ▁often ▁incorpor ated ▁into ▁vectors ▁to ▁allow ▁for ▁selection ▁of ▁successfully ▁trans du ced ▁cells . ▁ ▁CR IS PR - associ ated ▁end on uc lease : ▁Cas 9 ▁or ▁other ▁CR IS PR - associ ated ▁end on uc leases ▁such ▁as ▁C pf 1 ▁must ▁be ▁introduced ▁to ▁cells ▁that ▁do ▁not ▁end ogen ously ▁express ▁them . ▁Due ▁to ▁the ▁large ▁size ▁of ▁these ▁gen es , ▁a ▁two - vector ▁system ▁can ▁be ▁used ▁to ▁express ▁the ▁end on uc lease ▁separately ▁from ▁the ▁s g R NA ▁expression ▁vector . ▁ ▁Trans du ction ▁and ▁selection ▁▁ ▁C ells ▁are ▁typically ▁trans du ced ▁with ▁a ▁Mult ip licity ▁of ▁In fection ▁( MO I ) ▁of ▁ 0 . 4 ▁to ▁ 0 . 6 ▁l ent iv iral ▁particles ▁per ▁cell ▁to ▁maxim ize ▁the ▁lik elihood ▁of ▁obtain ing ▁the ▁most ▁amount ▁of ▁cells ▁which ▁contain ▁a ▁single ▁guide ▁R NA . ▁If ▁the ▁effects ▁of ▁simultane ous ▁perturb ations ▁are ▁of ▁interest , ▁a ▁higher ▁MO I ▁may ▁be ▁applied ▁to ▁increase ▁the ▁amount ▁of ▁trans du ced ▁cells ▁with ▁more ▁than ▁one ▁guide ▁R NA . ▁Selection ▁for ▁successfully ▁trans du ced ▁cells ▁is ▁then ▁performed ▁using ▁a ▁flu ores c ence ▁ass ay ▁or ▁an ▁ant ib