The Value of Multi-copy Markers
Several of the markers used in the Y-DNA tests at Family Tree DNA are called 'multi-copy' markers. A multi-copy marker is one where 2 or more copies of the marker exist at different locations on the Y-chromosome.† The names of a multi-copy markers include small letters, such as a or b, following the markerís DYS name. When selecting the markers for the various tests, Family Tree DNA included 1 or 2 multi-copy markers in each panel of markers, corresponding to the three Y-DNA tests currently available (12, 25 and 37). The 12 marker Y-DNA test has 1 multi-copy marker. The upgrade to 25 Markers has 2 multi-copy markers, and the upgrade to 37 markers also has 2 multi-copy markers. Inclusion of these multi-copy markers was very important, based on both scientific attributes of the Marker as well as the genealogical utility.
Multi-Copy Markers Used by FTDNA
12-Marker Test: 385a, 385b
25-Marker Test Upgrade: 459a, 459b and 464a, 464b, 464c, 464d
37-Marker Test Upgrade: YCA II a, YCA II b and CDY a, CDY b
For markers to have value to genealogical research, they must change slowly, but not so slowly that they can't differentiate lineage, but not change so quickly that closely related persons don't match. This criteria for markers for genealogical purposes is difficult to fulfill. Multi-copy markers meet this selection criteria and are excellent for genealogical purposes. Multi-copy markers appear to change more rapidly because with 2 copies (for example) you have twice the opportunity to see a change, which we genealogists see as a break in a lineage. Markers which change more rapidly are valuable to genealogical applications of DNA testing, to differentiate lines or branches. Markers are valuable in differentiating unrelated individuals and should show the same signs of a much older split in the lineage, but the use of multi-copy markers is especially helpful for identifying breaks within families.
Marker DYS464 appears to be a rapidly changing Y-chromosome marker and is a multi-copy marker. DYS464 occurs at least four times near the center of the Y-chromosome. The first four copies are called: DYS464a, DYS464b, DYS464c, and DYS464d. Marker DYS464 is also known to occur more than four times, generally in African lineages of Haplogroup E. Additional copies of DYS464 are called: DYS464e, DYS464f, and so forth. When more than four copies of DYS464 are found in a DNA sample, the results for all the copies are provided on your personal page at the Family Tree DNA web site.
DYS464 has an observed range between 9 to 20 inclusive. When testing a random sample of 679 males for DYS464, scientists have found that the result 15,15,17,17 occurred in 10.6% of those tested, 15,15,16,17 occurred in 7.5% of the samples, and all the other results occurred less than 5% of the time, with over half these results only occurring once. This illustrates that Marker DYS464 is valuable in differentiating unrelated persons or splits in branches that have failed to show variation with other markers in the panel. In fact DYS 464 alone has a greater ability to split then the first 12 markers combined.
The results for a multi-copy marker are reported in ascending order. For example, here are some results for DYS464:
11 11 14 16
12 14 15 16
Since the results are reported in ascending order for multi-copy markers, this must be taken into account when comparing the results of the Markers between individuals. For example, consider the following results:
Person 1: 15 15 17 17
Person 2: 13 13 15 17
At a glance, you may interpret these results has having 3 differences. The correct interpretation is 2 differences. To correctly interpret the results for this multi-copy marker, the results that match are not counted as differences. The 15 in the first person above matches a 15 in the second person, so the 15 is not counted as a difference, even though the two 15's do not line up in the display of the results. A 17 from the first example matches the 17 in the second person. The two 13's in the second person do not have a match in the first example, so in comparing these two results, the differences are 2.
Since multi-copy markers change more rapidly, these markers are an excellent tool to identify branches or lines. From a genealogical perspective, markers must change, but not too rapidly, as well as be stable, but not too stable. Multi-copy markers are very valuable, since they change more rapidly. By selecting a mix of markers that change slowly and therefore are relatively stable, as well as more rapidly changing single and multi-copy markers, Family Tree DNA has attempted to provide the best selection of markers for genealogical purposes. Multi-copy markers are a very important component of the marker mix, but they do require some understanding.