Chat
|
Daily Search
|
My GenForum
|
Community Standards
|
Terms of Service
|
|
|
People are often confused by the way results are reported for multicopy markers. They are the markers with small letters after them. There are actually two or more copies on the Y-chromosome. However, the usual tests cannot distinguish which values correspond to which physical location. The values are simply reported in numerical order. Forensic geneticists (and SMGF) report them without the letters, e.g., DYS385=11,14, which is reported by genealogical testing firms as DYS385a=11 and DYS385b=14.
When one value is reported for a duplicate marker (e.g., DYS385a=11 and DYS385b=11), it means that only one peak was observed. There is no way to know for certain whether there are actually two alleles or one. Since there are two copies most of the time, two alleles are reported. However, there could also be a deletion of one copy. Forensic geneticists report only the observed values, in this case DYS385=11.
For DYS385, there is a special test, called the Kittler test, which can distinguish between the two locations. Many people take it when there is a mutation to a single value in their family tree.
A more complicated situation exists for DYS464. Often two peaks of equal height are observed. They are reported as 4 alleles, the most common number, even though there could be two or six. If at least one peak differs from the others, the analyst can use relative peak heights to ascertain the number of alleles. Forensic scientists use both the conservative method (c-type), which reports observed values regardless of peak height, and the extended method (e-type), which resolves all of the alleles from peak heights.
However, peak heights vary considerably, so it is possible for an analyst to confuse different configuations. I had a case where a family had solid documentation, but the DYS464 values gave conflicting results. Two people had one set of values, while three others had another set of values. It seemed unlikely that analysts would make the same mistake twice. However, a review by the testing comapany showed that all five had the same values. Thus, it appears that running several electropherograms is the only way to be certain of DYS464 results.
Notify Administrator about this message?
Followups:No followups yet |
| http://genforum.genealogy.com/dna/messages/1458.html | ||
 |
Link to GenForum Add Forum |
|