View Full Version : Full Sibling or Half Sibling?

04-16-2014, 07:44 AM
I spent the last hour googling an answer, so I didn't have to bother anyone with this, but I am at wit's end.

I just received my sisters results back from ancestry and was surprised by the lack of mutual matches through our paternal side (I had previously tested my mother.)

I ran our raw data through gedmatch and it said that my sister and I share 2013cM. Are we half siblings, or could we still be full siblings with that low amount of shared cm's?

Thank you very much for answering!

PS The full result for the gedmatch one to one comparison was:
Largest segment = 103.3 cM
Total of segments > 7 cM = 2,013.2 cM
Estimated number of generations to MRCA = 1.4

Ann Turner
04-16-2014, 09:35 AM
Do you see some completely identical segments (color coded green) when you select the graphic bar option?

04-16-2014, 01:18 PM
Ann, thank you for responding! Yellow predominates, with red being the second most common color, however there is green interspersed throughout - Chromosome 21 seems to have the most. The two kit numbers I'm comparing are Kit A981748 (*PrmC) and A299526 (K M).
Any light you can shed would be most helpful! Thank you!

Ann Turner
04-17-2014, 11:52 AM
From your verbal description, it sounds a bit more like half siblings. Full siblings would see roughly 25% of the diagram color coded green in rather long segments. If you'd like to send me a screen print, you can e-mail me directly [email protected]

04-17-2014, 04:38 PM
I will share some data for several people.

04-17-2014, 04:48 PM
Look at line 2 - having 2048.17 gives range - Full Siblings, Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew
Look at line 3 - having 1784.38 - gives range - Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle , Niece/ Nephew

The longest block also plays a role

so you having 2013cM puts you in the range of Full Siblings, Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew

With which company did you test?

After some weeks I will have another result and will be able to provide another brother/sister relationship.

04-17-2014, 04:52 PM
Look at the other lines below - half-siblings can have as little as total 981.24 longest 55.19

I would bet you are full siblings.

If you have some concerns test a 1st cousin coming from the line that yous suspect that you do not share. the cousin should match the brother and the sister.

04-17-2014, 05:07 PM
My father and his sister share only one distant match in common. My father has 5 distant matches, my aunt has 15 distant matches.

The more the distant the matches the less the possibility to share between brother and sister. Since distant matches share small segments there is high probability that there will be no shared segments in both brother and sister lets say from the 4th great grandfather that is the common ancestor of the sister and the distant cousin.

In the case above my father and his sister both match a paternal 1st cousin and a maternal 1st cousin - yet they share only one distant cousin!