Value of FTDNA TiP calculator?

[billdickason]

I am administrator for a y-dna project.
I am continually puzzled by the results from the calculator for TMRCA. For example, I have two participants that match 65/67 and we know that the MCRA is 5 generations back. If you run TiP and input that MCRA must be back more than 4 generations, you get only a 40% probability that it is within 5 generations. Another example, I have a match of 110/111 with someone, and we know the MCRA must be beyond 5 generations.If I input 5 generations it shows a 45% probability that the MCRA is within the last 5 generations.

Does anyone find this information at all useful?

[Oshri]

The information is useful because it gives an estimate that should be valid in most cases. Sometimes the events with the lower probability occur, but not most of the time.

If the Tip calculator says 90% of TMRCA of 4 generations or less, then it implies that it wont be true for 10% of the tests.

for your exaple: 65/67 match with TMRCA of 5 means that two mutations occured over one generation. This is of course less probable then two mutations occuring over two generations or more.

[thetick]

It's only slightly better than throwing darts at the wall. It does demonstrate that DNA mutations are extremely unpredictable over a short period of time.

[ShellyH]

Testing a number of men whose shared ancestor was born in 1809 (the MRCA varies for each) has found that 65/67 is the norm. The mutations vary depending on family lines, but other than the siblings, each is 65/67 to each other. Interestingly, a fairly close match to an adopted man and his son to this same group of men found the father to be 64/67 and the son to be 63/67. In their case, a mutation has been pinpointed to a specific generation.