Sunday, June 30, 2013

Which Autosomal DNA Test Should You Take?


The DNA testing marketplace continues to evolve rapidly. What would cost about $400 just 3 years ago can now be purchased for about $99. It is hard to imagine that this level of price cutting can continue. But wouldn't it be nice for us DNA junkies if they could? Not only could we take more tests. Many more potential cousins would add their information to DNA databases.

Until FTDNA's just announced Sizzling Summer Sale, it was cheaper to take 23andMe's test at $99 and then transfer your downloaded raw data to FTDNA at $69 than it was to pay full $289 for Family Finder. Now that FTDNA has (at least for the next few weeks) reduced Family Finder to $99 this economic incentive may not be as strong. However, starting with 23andMe and transferring your data allows you to fish in both databases for cousins. It also allows you to take advantage of the analytical tools of both companies AND the health related information of 23andMe. FTDNA allows 3rd party transfer from Ancestry's autosomal data as well.

However, FTDNA is the only company that accepts raw data from another lab test. It also is the only one that is now storing DNA samples for future testing. This can only be taken advantage of if FTDNA was the original tester of your sample. This is particularly important when the person being tested is elderly so that their sample is available for tests that may become available in the future. 


When you are on a limited budget, you need to weigh what you may learn from further analyzing your own genome vs what you potentially could learn from testing another family member. Y-DNA testing of a sibling (male) will generally give identical results as those of the first brother tested. With mitochondrial DNA testing this is true for siblings of both sexes. However, with autosomal DNA testing sibling testing does not give identical or near identical results. In general siblings share about 50% of their autosomal DNA. However, they can range from as low as 37% to as much as 63%. This is not critical if one is trying to match 2nd cousins or closer relatives. It does start to matter when one is seeking to find 3rd cousins or more distant relatives.

When fishing for cousins in any company's database, you and any of your siblings will be almost certain (more that a 99% chance) to match a 2nd cousin. At the 3rd cousin level your chances (and those of a sibling) for matching someone in a given database are about 90%. At this level of cousinhood it is still likely that you will be matching most of the same individuals that your siblings match. However, at the 4th cousin level, you and each of your siblings will have only about a 50% chance of matching a particular individual in the database who is in fact a cousin. Your match list and those of your sibling(s) will start to vary considerably. At the 5th cousin level and more distant very significantly. Each of you will match with about 10% to 15% of your actual cousins in the database but many of them will be different individuals. Beyond 5th cousins you will still get lots of matches because you have so many cousins at this level. However, you (and a sibling) will each have a less that 2% chance of matching a particular cousin in a database. 

Since the matching efficiency declines down this slippery slope with each generation, it is important to test the oldest possible member of your family for best autosomal results. This is only marginally true with Y-chromosome or mitochondrial DNA testing.

All of this is important to keep in mind when you are allocating your limited dollars and deciding which test to take AND which family member to test. 23andMe currently offers $20 off additional test kits when they are ordered at the same time. 

Happy testing and may you find lots of new cousins!
         

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