Just a minor point of correction in all this, Bunnahabhain. You wrote
"Similarly for a Woman, if she has no daughters, her mitochondrial DNA line is broken."

This is not quite correct, as her mitochondrial DNA is carried in all her cells, and thus all her eggs, including those that get fertilised by sperm containing Y chromosomes and which consequently produce sons.

Being the pedant that I am, I occasionally wonder when the corrections to chronological calculations will start coming in. The "Mitochondrial Clock" notion is based on at least three assumptions, all quite reasonable at first sight. One is that the rate of mutation in the DNA is constant; since we started measuring it the evidence doesn't seem to contradict this assumption. A second assumption is that it has always been constant. This is what they thought about radiocarbon dating when it was first discovered and applied in the 1950s; some subsequent anomalies were explained when they discovered variation in the rate of production of C14. Other subsequent anomalies were explained when they discovered that organisms living in an environment rich in 'old' organic carbon (that had much of its C14 already depleted) were taking up that carbon, leading to biassed 'elapsed time since death' calculations.

This latter anomaly could be described as 'leakage' of the datable material. The third assumption about mitochondrial DNA is that all of it in any given cell is maternal in origin. There is evidence of leakage of paternal DNA (from the fertilising sperm) into the cell of the fertilised egg and thus the consequent zygote, foetus and adult. It is described as 'leakage', the material leaked is datable, as it contributes to the set of DNA that is used for dating, and must affect 'apparent' rates of mutation and thus any age consequently calculated.

I dare say there's more than a couple of PhD dissertations available for keen students.

Cheers, Rowan