DYS is short for DNA Y-chromosome Segment, and is used to designate a segment of DNA on the Y chromosome where a sequence of nucleotides repeats. These sequences are known as short tandem repeats (STRs), and are called markers in genealogical DNA testing. The possible variations of repeats at a DYS marker are known as alleles.
Some testing companies have different formats for the way DYS markers are written, for example, the location 455 may be written as DYS455, DYS 455, DYS#455, or DYS# 455.
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