Very interesting! I'm not sure I agree with your reasoning for the mitochondrial mutation point:
> * Mitochondrial DNA is passed by mothers only and so undergoes very little mutation
It's true that mothers pass on mitochondrial DNA but this doesn't necessarily require the absence of mitochondrial DNA mutations. I would imagine the lower rates of DNA mutation are due to the importance of the mitochondrial genome for generating a cell's energy.
The mutation rate of mitochondrial DNA is much faster than in nuclear DNA [1]. But mitochondrial DNA does not have crossover, so the mutation tree is much easier to build.
> Human mitochondrial DNA has been estimated to have mutation rates of ~3× or ~2.7×10−5 per base per 20 year generation (depending on the method of estimation); these rates are considered to be significantly higher than rates of human genomic mutation at ~2.5×10−8 per base per generation. Using data available from whole genome sequencing, the human genome mutation rate is similarly estimated to be ~1.1×10−8 per site per generation.
I would expect the mutation rates of mitochondrial and nuclear DNA to be about the same, unless the mitochondria have additional repair proteins not involved with nuclear DNA, or the shorter length of the mitochondrial chromosome affects the rates, or some other process I'm not familiar with. I think maybe parent meant to refer to diversity, not mutation. With nuclear DNA, the offspring chromosomes are made up from a combination of the parents' DNA. There's a lot of swapping and mixing and matching that takes place. This adds diversity to the population.
