Question

G2G: Can i use my sisters DNA to track mymine?

Answer 1

Your autosomal DNA and your sister's will be similar, but you will not each have inherited exactly the same segments from each of your parents. So it's always a good idea to have DNA tests from each sibling. You will each end up sharing some DNA from more distant ancestors that the other does not share. If you want to include your sister's DNA test information on WikiTree you will need to invite her to join WikiTree and enter her own DNA test information to her profile. It would not be appropriate for you to display her DNA test information (like a GEDMatch ID) on your own profile.

Answer 2

Since full siblings have exactly the same ancestors, DNA matches from one sibling are applicable to the other siblings.

For example, if someone is 1st cousin to your full sister, they are also 1st cousin to you.

In most cases, if you have an autosomal DNA test for one sibling, testing additional siblings does not add very much information. Each sibling receives a different mix of the parents DNA, and may match relatives to different degrees. However, most of the matches will be duplicated between siblings.

Comments

Whether matches will be duplicated between siblings depends on the strength of the match.  I.e., siblings will certainly match the same first cousins, but not necessarily the same third or fourth cousins, etc.  I've found my siblings' DNA tests to be quite useful in my DNA analysis.

Edited to fix typo.

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I agree with Julie. Genealogically--meaning in this case the paper trail only--the ancestors of full siblings will be identical. However, there is much to be gained by testing the DNA of siblings.

Biologically, any two full siblings will share, by our common DNA tests which report half-identical sharing regions, roughly 35% to 45% of their DNA. Per 23andMe, that sharing range is 38% to 61%.

Fifty percent sharing between siblings is what would be theoretically expected (not to confuse things, but all services other than 23andMe will report sibling sharing in percentages and centiMorgans as being about 37.5%, not 50%; an explanation is in this G2G post from three weeks ago). So, again theoretically, we can use a simple formula to estimate how much of the parents' total genomes is passed down based on the number of children they have: 1-0.5ⁿ where n is the total number of siblings. Running with that, we see--again as an estimate--that with two children, 25% of the parents' combined genomes will not have been passed down to the next generation. With three children, the uninherited DNA would be around 12.5%; four children, 6.25%; five children, 3.125%, and so on.

If everything divides up fairly evenly, you'd need 10 children to reach a 99.9% chance that both parents' DNA had been passed along. This is one of several factors that drives the drop-off, after 2nd cousins, that two more distant cousins will share any meaningful DNA, as Julie mentioned (see Amy Williams's handy chart here).

So even in a large nuclear family, there is usefulness in testing siblings. And this is also a reason for all those unfortunate YouTube videos where the uninformed try to get a ton of "likes" by revealing the positively shocking information that two siblings took a DNA test and show different admixtures in the list of countries they're "from."

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I didn't say that siblings tests were of no value, just that they *are* applicable and largely similar. I wouldn't see the point of testing multiple siblings for casual genealogical curiosity, but if something interesting comes up, then sure. I tested my own sibling immediately when I realized there was an NPE to be investigated! (For just the reasons you said.) I'm glad I did -- it gave me more matches and more confidence in my matches. I approve of you doing the math here.

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Hmm.  I don't suggest spending any money on "casual genealogical curiosity."  Many testers don't have a clue of the value of DNA testing, nor do they know how to use it, and only want to know if they should wear a kilt or lederhosen (which won't be very accurate, and not worth $69 or $99).

A use for sibling testing that I didn't mention the first time is in the creation of chromosome maps, which can be done using a method described by Blaine Bettinger here. 

Edited to make additional point.