|  | | The Y-chromosome contains 59 million bits of information, each of which is encoded by a "base pair." Looking at all of these base pairs is impractical, so geneticists have identified a number of specific chromosome locations that can be used for analysis and comparison.
These unique locations are generally called "markers" and when they occur on the Y-chromosome, they are typically given names starting with "DYS".
At some Y-chromosome locations, there are small segments of base pairs that are repeated in the DNA. Markers with these types of repetitions are called "STR markers," where STR means "Short Tandem Repeat."
For instance, a particular genetic sequence at marker location DYS391 might be:
TGTCTG/TCTA/TCTA/TCTA/TCTA/TCTA/TCTA/TCTA/TCTA/TCTA/TCTA/TCTGCCT
Note there are ten repeats of the segment TCTA. The number of repeats is the "value" that is shown on a Y-DNA test report for the marker.
In this example, a lab report would show DYS391=10 for this marker.
Markers DYS385, DYS459, and YCAII are often called "duplicate markers" since they have two values for each marker location. SMGF considers these locations as a single marker with two values, rather than two separate markers (e.g. DYS385a and DYS385b).
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