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Why you may not look like your parents.
http://blairgenealogy.com/dna/dna101.html
Thanks to my wife who was discussing this subject on the " All my Chidren " forums And got me into the debate... ( AMC ????daytime soap opera ??? ).
Some crazy stuff .....
An individual's test results have little meaning on their own. You cannot take these numbers, plug them into some formula and find out who your ancestors are. The value of the test results depends on how your results compare to other test results. And even when you match someone else, it will only indicate that you and the person you match share a common ancestor. Depending on the number of markers tested and the number of matches it will indicate with a certain degree of probability how long ago this common ancestor existed. It will not show exactly who this ancestor is.
As discussed above, the Y-Chromosome is passed from father to son. The vast majority of the time the father passes an exact copy of his Y-Chromosome to his son. This means that the markers of the son are identical to those of his father. However on rare occasion there is a mutation or change in one of the markers. The change is either an insertion or a deletion. An insertion is when an additional repeat is added to a marker. A deletion is when one of the repeats is deleted.
Mutations occur at random. This means it is possible for two distant cousins to match exactly on all markers while two brothers might not match exactly. Because of the random nature of mutations we must use statistics and probability to estimate the Time to the Most Recent Common Ancestor (TMRCA). The actual calculations of TMRCA are mathematically complex and depend on knowing the rate of mutation and the true number of mutations. At this time there is not enough data to accurately determine either of these factors so certain assumptions have to be made. The discussion of these assumptions and the actual calculations are beyond the scope of this webpage. For those wishing to read more about the various models used, I recommend Time to Most Recent Common Ancestry Calculator by Bruce Walsh. The simplest and one of the most commonly used models makes the following assumptions:
Rate of Mutation = .002. This assumes that any given marker has a .002 chance of mutating with each generation. In other words, we could expect any marker to mutate once in 500 generations. The rate of .002 is considered conservative and is the average of a number of studies. It will result in a TMRCA that is longer than higher mutation rates.
Number of mutations: This model counts any change in a marker as a single mutation. Each marker is scored as either a match or a non-match. If a marker does not match it is assumed to be a single mutation. This method a counting mutations may result in underestimating the TMRCA.
Based on the above assumptions we derive the cumulative probability table below. This table simply list the number of generations corresponding to the 50%, 90% and 95% probability levels for various numbers of matches.
http://blairgenealogy.com/dna/dna101.html
Thanks to my wife who was discussing this subject on the " All my Chidren " forums And got me into the debate... ( AMC ????daytime soap opera ??? ).
Some crazy stuff .....