▁variety ▁of ▁path og ens ▁that ▁can ▁attack ▁the ▁body . ▁Me as uring ▁the ▁differences ▁and ▁the ▁rate ▁of ▁change ▁in ▁DNA ▁content ▁at ▁the ▁single - cell ▁level ▁can ▁help ▁scient ists ▁better ▁understand ▁how ▁path og ens ▁develop ▁ant ib i otic ▁resistance , ▁why ▁the ▁imm une ▁system ▁often ▁cannot ▁produce ▁ant ib od ies ▁for ▁rapidly ▁mut ating ▁vir uses ▁like ▁H IV , ▁and ▁other ▁important ▁phen omena . ▁ ▁Many ▁techn ologies ▁exist ▁for ▁sequ encing ▁genom es , ▁but ▁they ▁are ▁designed ▁to ▁use ▁DNA ▁from ▁a ▁population ▁of ▁cells ▁rather ▁than ▁a ▁single ▁cell . ▁The ▁primary ▁challenge ▁for ▁single - cell ▁gen ome ▁sequ encing ▁is ▁to ▁make ▁multiple ▁copies ▁of ▁( am pl ify ) ▁the ▁DNA ▁so ▁that ▁there ▁is ▁enough ▁material ▁available ▁for ▁the ▁sequ encer , ▁a ▁process ▁called ▁whole ▁gen ome ▁ampl ification ▁( W GA ). ▁Typ ical ▁methods ▁for ▁W GA ▁consist ▁of : ▁( 1 ) ▁Multiple ▁Dis p lacement ▁Am pl ification ▁( MD A ) ▁in ▁which ▁multiple ▁prim ers ▁an ne al ▁to ▁the ▁DNA , ▁polym er ases ▁copy ▁the ▁DNA , ▁and ▁knock ▁off ▁other ▁polym er ases , ▁free ing ▁str ands ▁that ▁can ▁be ▁processed ▁by ▁the ▁sequ encer , ▁( 2 ) ▁PC R - based ▁methods , ▁or ▁( 3 ) ▁some ▁combination ▁of ▁both . ▁ ▁Vari ation ▁in ▁met abol omic ▁properties ▁C ells ▁vary ▁in ▁the ▁met abol ites ▁they ▁contain , ▁which