Determining if 1,814cM match from AncestryDNA is Half Sibling?

Question

My son recently had a match come up as close family the match is male and 1814cm.

His only living grandfather is already in our tree at 1857cm. All other grandparents are deceased and have never participated in Ancestry DNA.

When I review the shared matched between my son and the matched male they have matches consistent with my ex-husbands family. However none of my ex husbands brothers (his uncles) have done DNA testing.

My son has no grandchildren.

Is it possible that 1814cm could be the child of one of my ex husbands brothers children or am I looking at the possibility that there is a half sibling to my son?

Answer 1

You only mention his fraternal uncles, and not whether he has any fraternal aunts or maternal aunts/uncles available to test.

The Shared cM Project 3.0 tool v4 relationship suggestions for 1,814cM are:

• Grandparent
• Aunt / Uncle
• Half Sibling
• Niece / Nephew
• Grandchild

If it is not possible that your son has any nieces or nephews (you do not say), then you seem to have eliminated the others, and so I think that just leaves half sibling to be examined in more detail.

You will also see at the link provided above that a Great-Aunt/Uncle to Great-Niece/Nephew could come into consideration but it says that:

this set of relationships is just within the threshold for 1814cM, but has a zero probability in thednageek's table of probabilities

Answer 2

1,814 cM can be a half-sibling, but it can also be an aunt/uncle, niece/nephew, grandparent, grandchild or a double first cousin.

As you mentioned that the match is male and could not be his grandfather, uncle or grandchild, there are 3 possibilities:

1. Nephew
2. Half-sibing
3. Double first cousin

If your son doesn't have any nephews, we could eliminate that as well. If you don't have any siblings or you know that none of your siblings have met one of your ex-husband's siblings, we could also eliminate the double cousin possibility.

This leaves us with half-sibling. Unless your ex-husband has an identical twin, the match must be your ex-husband's child. That means your son has a half-sibling.

So the match may or may not be a half-sibling.

Answer 3

That person is his half sibling. 1600-2000 is in the range of above mentioned. Grandparents Nephew and grandchildren have all been ruled out. Only leaves half sibling. I found 2 half sisters and 3 half brothers via dna testing. They all have the same father. Evidently the same father fathered me in another country. I knew I was adopted so I couldnt deny it. They are all happy about me but I am still on the fence. Congrats to your son!