Half Siblings & Shared DNA

Kathy Hewelt

I have a situation in my family where 2 individuals (who were thought to be full siblings) appear to be half siblings based on their DNA tests in Ancestry (who lists them as "first cousins"). I am wondering if there is a possibility that the two fathers of the half siblings could have been first cousins themselves. The two half siblings share 30% DNA, and 2070 cM across 62 segments according to Ancestry. If the fathers had been fiirst cousins, would the amouns of shared DNA be a bit higher than those I've listed above? Is their any chance that the two half siblings could actually be first cousins? Thanks in advance. 

C D McBride

Kathy,

FamilySearch/Family Tree does not have the ability to determine or interpret the meaning of DNA results from any source. Such determinations need to be considered by someone who deals with DNA results such as you describe.

FamilySearch does have some information about the use of DNA that is available at this link if your care to review this a bit: https://www.familysearch.org/help/helpcenter/lessons/dna-an-introduction-to-genetic-genealogy-what-is-dna

Amy Archibald

FamilySearch also offers this educational site for DNA: https://www.familysearch.org/dna-testing

PeterLiepmann

WIKITree.org accepts DNA uploads.

Also https://www.gedmatch.com/

Was there a match on an X chromosome? If so you share a mother or possibly other first degree female relatives.

PeterLiepmann

In inbred communities, people with no known relationship closer than 4th cousin may show up as 3rd cousins.

Graham Buckell

You could try posting your question on the AncestryDNA Matching group on Facebook.

JeffreyBryant1

The DNA Painter Shared cM Project indicates that with 2070 cM of shared DNA there is a 10% probability the two individuals are full siblings, so don't rule that out yet. You may have to look at their other DNA shared matches.