DNA Test Results

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. That must be investigated through traditional genealogical research.

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.