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My half-sister and I recently completed DNA tests with myHeritage.com. The results don't show us having matching DNA. We share the same father.

Is it possible that we are half siblings even though there is no DNA match?

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If you are really half-sibling, and you took the test from correct people, you WILL have a shared DNA. A half-siblings share ~25% of DNA between each other. Or 1300-2300 cM.

The chances that the examples were accidentally mixed in laboratory are very small.

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In a prior answer it was stated that you would share between 1200 and 2300 cM of DNA. This is the primary way to validate if you are true half-siblings.

But, you might also want to compare your close matches with the matches that your tested half-sibling shares. Do both of you have matches that are the same DNA donors? If so, you might want to pursue those matches and see how you are related to them (who are your common ancestors). If you don't share any similar matches then it's even more probable that you are not half-siblings.

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Yes it's possible - assuming you are both female you will share an entire x chromosone which ancestry and my heritage do not test for - but gedmatch.com does. It's possible to not share any autosomal DNA with a half sibling as hereditary of the same chromosones from a a parent varies even with full siblings. Upload your DNA data on gedmatch if you are sisters and compare you x DNA...of course won't work between male/female siblings. I am curious though if you went that route what did you learn? Are you siblings (I'm going through this right now too)

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    You are completely wrong about this. To quote from the correct answer "half-siblings share ~25% of DNA between each other. Or 1300-2300 cM." – ColeValleyGirl Jul 27 '18 at 17:55
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I have read an article from a DNA scientist that said there is a 1 in 10,000,000 chance for FULL SIBLINGS to NOT MATCH at ALL on Autosomal DNA. No known case has been known to exist, as would be very hard to detect anyway, as would need both parents DNA in first place to confirm. How could this occur in theory, by each sibling having the exact OPPOSITE DAD/MOM section of the DNA-for all regions of the DNA. I would imagine the ODDS for Half Siblings are less than the 1 in 10,000,000. For cousins-ever lower-but again-pretty much impossible to ever identify or confirm. Someday, with all the DNA now on file, a known case may someday surface-but will be super rare-like winning lotto-but some do win. All this being said, it is HIGHLY unlikely to be anyone's answer to a non match. One would need both parents DNA to test, then both Siblings. So, I'm not suggesting this is someones answer, but just to point out, just when you think you know all the answers there may be some rare exceptions.

Also, chimerism can cause some odd DNA readings as well as 'Double Cousin".

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    Hi, Welcome to G&FH.SE! I have down-voted your answer because it is low quality. First of all, suppose someone wanted to read the article you cited. Your reference to the article is too vague to be of use. Your answer could be improved by 1) putting your statement that the answer contains edge cases at the very top and 2) including a concise list of cases with links to relevant articles. Your answer could also be improved by less use of upper case. – Jan Murphy Dec 21 '19 at 19:10
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PaternityUSA.com's sibling DNA test analyzes the DNA of alleged brothers or sisters to determine if they are full siblings, half siblings or not related. Their Sibling tests can help prove or disprove the paternity or maternity indirectly when the alleged father or mother is unwilling or unavailable to be tested. The DNA test for siblings that they offer can analyze Up To 35 Markers, which is almost 50% more markers then their competitor’s 24 marker DNA test. The results will show if the test participants are full siblings (both parents in common), half siblings (one parent in common) or not related as brother and sister. This is accomplished by actually comparing one alleged sibling against the other alleged sibling tested, and not just by using an ancestry database.

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    Avoid overt self-promotion. The community tends to vote down overt self-promotion and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, that’s okay. However, you must disclose your affiliation in your answers.](genealogy.stackexchange.com/help/behavior). In practice this means any answer that recommends your own product must include something like "Disclosure: I am the [position] of [company] that develops/distributes this software/test". – PolyGeo Aug 1 '19 at 3:37

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