▁is ▁a ▁start ling ▁result . ▁Add itional ▁NUM T s ▁with ▁similar ▁ph y log en ies ▁indicate ▁that ▁such ▁events ▁may ▁be ▁not ▁unique . ▁ ▁Another ▁problem ▁arose ▁from ▁the ▁presence ▁of ▁NUM T ▁in ▁the ▁gen ome ▁associated ▁with ▁the ▁hard ship ▁of ▁con cluding ▁the ▁exact ▁number ▁of ▁mit och ond rial ▁insert ions ▁into ▁the ▁n D NA . ▁Det erm ining ▁the ▁exact ▁number ▁of ▁NUM T ▁pseud ogen es ▁for ▁a ▁species ▁is ▁difficult ▁task ▁for ▁several ▁reasons . ▁One ▁reason ▁that ▁makes ▁detection ▁of ▁NUM T ▁sequences ▁more ▁difficult ▁is ▁the ▁alter ation ▁of ▁these ▁sequences ▁by ▁mut ation ▁and ▁delet ion . ▁ ▁Two ▁further ▁substantial ▁obst acles ▁make ▁recognition ▁of ▁NUM T ▁very ▁difficult ; ▁first ▁is ▁the ▁lack ▁of ▁correlation ▁between ▁the ▁proportion ▁of ▁non c oding ▁n D NA ▁and ▁the ▁number ▁of ▁NUM T ▁inser ts ▁in ▁the ▁nuclear ▁gen ome . ▁That ▁is , ▁NUM T ▁insert ion ▁could ▁occur ▁in ▁the ▁known ▁or ▁predicted ▁coding ▁region , ▁both ▁intr on ▁and ▁ex on , ▁rather ▁than ▁only ▁in ▁inter gen ic ▁and ▁intr onic ▁region . ▁ ▁Second , ▁mit och ond rial ▁DNA ▁integrated ▁into ▁animal ▁nuclear ▁genom es ▁is ▁primarily ▁limited ▁to ▁animals ▁with ▁circular ▁mit och ond rial ▁genom es ▁without ▁intr ons . ▁NUM T ▁studies ▁are ▁not ▁available ▁in ▁animals ▁with ▁linear ▁mit och ond rial ▁genom es ▁or ▁those ▁with ▁intr on - cont aining ▁mit och ond ria . ▁Therefore