Comparison With Short Tandem Repeats (STRs)
The properties of UEPs can be contrasted with those of short tandem repeat sequences (STRs), the other main type of genetic variation used in genealogical DNA testing.
Unlike UEPs, STR sequences are highly variable. There is a significant probability that one of a set may have changed its repeat number after only a few generations. That makes a particular STR haplotype much more specific, matching a much smaller number of people. But, it also means that, at least in the case of Y-STR markers, quite unrelated lineages may have converged to the same combination of Y-STR markers entirely independently by different routes. Matching Y-STR markers by themselves cannot be used to indicate genetic relatedness.
The exception is those few cases where Y-STR markers can take on the status of UEPs. This is the case of the occurrence of a large-scale deletion event, which caused a sudden big change in the Y-STR repeat number, rather than the usual single increment or decrement. Such an occurrence can be considered to have been a unique one-off in a group of lineages. Such a change in the Y-STR DYS413, for example, distinguishes subgroup J2a1 from J2a in Y-DNA haplogroup J.
Read more about this topic: Unique-event Polymorphism
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