Why is (in forensic genetics) in some cases more appropriate comparison of nuclear DNA but in some other cases comparison of mitochondrial DNA?

Is it because geneticists are sometimes unable to find nDNA or if nDNA is too damaged? Also could it be because of the structure of mtDNA (it's more protected against degradation, which is good for identifying old biological material)? I can't see any other advantages, since mitochondrial DNA mutations occur frequently, due to the lack of the error checking, but are there any that I am missing?

Thank you in advance.

  • $\begingroup$ Degradation of mDNA is more difficult than nDNA as you said and it's present in more copies. But also, in some cases, when you just want to know the identity of the victim, and you already suspect who it might be, it can be compared the mDNA with the mother/brother/sister/grandmother. It can be useful as well to know the geographical ancestry. $\endgroup$ Oct 18 '17 at 16:59

mtDNA is present in a much higher copy number per cell than nuclear DNA.

According to this paper, there are approximately 4000 or so mitochondrial DNA copies per human muscle cell.

copy number of mtDNA per diploid nuclear genome in myocardium was 6970 ± 920, significantly higher than that in skeletal muscle, 3650 ± 620 (P = 0.006).

This makes it far more likely that a non-degraded copy of mtDNA exists, considering that there are normally only 2 or 4 copies of nuclear DNA per cell per locus for almost all kinds of cells.

  • $\begingroup$ Doesn't a cell (or at least a human cell) usually have one copy of nDNA, only in phase S they can have two? When would it have 4 copies? $\endgroup$ Apr 16 '15 at 19:15
  • 1
    $\begingroup$ @cherry8.8vanilla Humans are diploid, therefore "2 copies". Arguably if you consider the 2 alleles from each parent (which might be different) you can call it 1 copy as well. $\endgroup$
    – March Ho
    Apr 16 '15 at 21:32

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