ural ▁gen es ▁and ▁dis rupt s ▁or ▁al ters ▁the ▁vital ▁cell ▁processes . ▁For ▁instance , ▁in ▁primary ▁low - grade ▁brain ▁ne op las ms , ▁flu ores cent ▁in ▁situ ▁hy brid ization ▁analysis ▁helped ▁with ▁the ▁recognition ▁of ▁m t D NA ▁local ized ▁in ▁the ▁nucle us ▁in ▁correlation ▁with ▁an ▁overall ▁increase ▁in ▁m t D NA ▁content ▁in ▁the ▁cell . ▁This ▁ont ogen ically ▁early ▁event ▁is ▁important ▁in ▁the ▁et i ology ▁of ▁these ▁tum ors . ▁Similarly , ▁in ▁he pat oma ▁cells ▁m t D NA ▁sequences ▁are ▁present ▁in ▁the ▁nuclear ▁gen ome ▁at ▁a ▁higher ▁copy ▁number ▁in ▁contrast ▁with ▁the ▁normal ▁t issues . ▁Another ▁example ▁would ▁be ▁He La ▁n D NA ▁that ▁contains ▁sequences ▁which ▁hy brid ize ▁with ▁m t D NA ▁fragments ▁of ▁approximately ▁ 5 ▁k b . ▁An ▁analysis ▁showed ▁that ▁n D NA ▁of ▁m align ant ▁cells ▁contains ▁sequences ▁of ▁the ▁mit och ond rial ▁cy to chrome ▁ox id ase ▁I , ▁N D 4 ▁, ▁N D 4 L ▁, ▁and ▁ 1 2 S ▁r R NA ▁gen es . ▁Based ▁on ▁these ▁find ings , ▁m t D NA ▁fragments ▁were ▁assumed ▁to ▁act ▁as ▁a ▁mobile ▁gen etic ▁element ▁in ▁the ▁init iation ▁of ▁car cin ogen esis . ▁Southern ▁bl ot ting ▁is ▁the ▁method ▁used ▁to ▁determine ▁the ▁frequency ▁of ▁mit och ond rial ▁insert ion ▁in ▁n D NA ▁of ▁the ▁normal