▁using ▁these ▁techniques ▁to ▁el uc id ate ▁the ▁activity ▁and ▁function ▁of ▁gen es ▁in ▁a ▁way ▁never ▁possible ▁before ▁their ▁unique ▁approach . ▁ ▁Method s ▁There ▁are ▁two ▁basic ▁technical ▁approaches ▁to ▁produce ▁gen et ically ▁modified ▁m ice . ▁The ▁first ▁involves ▁pron uc lear ▁injection ▁into ▁a ▁single ▁cell ▁of ▁the ▁mouse ▁emb ry o , ▁where ▁it ▁will ▁randomly ▁integrate ▁into ▁the ▁mouse ▁gen ome . ▁This ▁method ▁creates ▁a ▁trans gen ic ▁mouse ▁and ▁is ▁used ▁to ▁insert ▁new ▁gen etic ▁information ▁into ▁the ▁mouse ▁gen ome ▁or ▁to ▁over - express ▁end ogen ous ▁gen es . ▁The ▁second ▁approach , ▁pione ered ▁by ▁Oliver ▁Smith ies ▁and ▁Mario ▁Ca pec chi , ▁involves ▁modifying ▁emb ry onic ▁stem ▁cells ▁with ▁a ▁DNA ▁construct ▁containing ▁DNA ▁sequences ▁hom olog ous ▁to ▁the ▁target ▁gene . ▁Emb ry onic ▁stem ▁cells ▁that ▁re comb ine ▁with ▁the ▁genom ic ▁DNA ▁are ▁selected ▁for ▁and ▁they ▁are ▁then ▁inject ed ▁into ▁the ▁m ice ▁bl asto c yst s . ▁This ▁method ▁is ▁used ▁to ▁manipulate ▁a ▁single ▁gene , ▁in ▁most ▁cases ▁" k no ck ing ▁out " ▁the ▁target ▁gene , ▁although ▁increasing ly ▁more ▁subt le ▁and ▁complex ▁gen etic ▁manip ulation ▁can ▁occur ▁( e . g . ▁human isation ▁of ▁a ▁specific ▁protein , ▁or ▁only ▁changing ▁single ▁nucle ot ides ). ▁ ▁Us es ▁ ▁Gen et ically ▁modified ▁m ice ▁are ▁used ▁extens ively ▁in ▁research ▁as ▁models ▁of