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TMRCA value or not

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  • TMRCA value or not

    What is of more value, the TMRCA of a marker or date of original ybp of formation of a marker ?

  • #2
    Both are useful, depending on your purpose.

    Formation date tells you when the subclade split off from its parent clade. This is much less likely to change over time, because it's locked into the rest of the tree.

    TMRCA tells you when the constituents of the subclade began to diverge. This may change over time as more constituents appear.

    For example, take a look at YFull's haplotree for I-L161 (often called "Isles," arguably a misnomer). Notice the newly discovered offshoot at the bottom of the page, I-Y13330. It split off from the rest of I-L161 about 6800 years ago; that age will not change much. Its current TMRCA is only 150 ybp, because so far, only two men of the same surname have been found to belong to this newly discovered clade. Over time, it is extremely likely that we will find someone else, more distantly related to the other two; that will immediately increase the TMRCA dramatically. Eventually, the TMRCA might approach the formation date (or it might not).