The more people who participate in genealogical DNA testing, the more potential relationships can be found.

The fact that there are several testing venues available seems to work at cross purposes to that goal, because you may have your DNA tested by 23andMe, while a long-lost cousin may have his tested at, say, Family Tree DNA (FTDNA).

There may be valid reasons for the choice of provider. As in my case, one venue may fail to extract enough genetic material from a sample, while another has no problem doing so. One venue may offer comparison of health- and medical-oriented genome characteristics, another might not.

FTDNA offers the option to join “surname projects,” in which others researching similar surnames can share information and wish lists; 23andMe does not offer such projects, etc.

Fortunately, there are some ways for users of diverse DNA-testing venues to compare their results to those of subscribers to other venues.

For example, in certain cases, raw genealogical data may be downloaded by a subscriber of 23andMe or AncestryDNA and uploaded to FTDNA for a cost that is less than FTDNA’s $100 testing cost. The genomes from the other venues can then be compared to those of FTDNA subscribers, FTDNA’s surname projects can be joined, etc.

Unfortunately, FTDNA is not yet programmed for 23andMe’s latest data format, and only older records can be uploaded.

A site that gets around such problems is the free site GEDmatch. It accepts raw data from several vendors. Users provide their contact information and give permission for their email addresses to be posted.

This is an advantage over 23andMe, for example, since correspondence can be made directly via email, rather than by anonymous correspondence through the vendor. However, some participants who freely give their email address still don’t respond to emails!

GEDmatch has more detailed graphs of segment matches within chromosomes than does 23andMe. Like 23andMe, GEDmatch allows you to set the significant length of segments to be considered (a match of seven centiMorgans or more is generally considered significant), but through color-coding, it also shows shorter segments that are shared.

GEDmatch allows one-to-one and one-to-many comparisons. The former are similar to comparisons on 23andMe but with more detail in the graphs. The one-to-many comparisons list all users who have a match of at least seven cM and include the length and number of matching segments, an email address, the percent of matching DNA, and the estimated number of generations to a common ancestor.

Interestingly, some relatives whose DNA I compared to mine on both 23andMe and GEDmatch show slightly different results: a matching segment being 23 cM in one and 24 cM in the other or a segment match in three chromosomes rather than in just two.

Since the raw data in both cases is identical, this seems to reflect differences in the software algorithms used by each venue. So some of the error in the analyses is not just lab error in extracting genetic material from my saliva, but computer error in the sense that two programs analyzed the same data and produced different results (even if minutely).

An aspect of DNA testing that I haven’t addressed is the use of a subscriber-provided family tree. In one way or another, most venues allow participants to enter their own family trees into the system: 23andMe has a routine wherein you start with your own name and add ancestors online, until the tree is as complete as you want it; GEDmatch allows uploading of a family-tree data file created by an offline program; and AncestryDNA links to Ancestry.com trees entered in either fashion.

While I otherwise encourage researchers to share their trees online, in order to make connections with others who may be researching similar information, I hesitate to upload my tree to a DNA testing site, and I have not done so as yet. Next time, I’ll tell you why not.