What is a Half 2nd Cousin?

[mlrfn448]

My son has undertaken a DNA search with 23andme, and in the results tree, it has described some name matches as 'Half 2nd Cousin, once removed'.
It is higher than my cousin's daughter (whose name I have recognised), who is described as 'Half 3rd Cousin'.
I really do not understand the 'half' bit.
I realise that these things are not entirely exact, but it would help to know how far back I need to check in my family tree.

[Gadget]

I'd look at the shared cMs rather than the website's relationship estimate. Then use the following to see what the possible relationships are:

https://dnapainter.com/tools/sharedcmv4

Gadget

[mlrfn448]

I can't find where it gives that on 23andme, tho ancestry has it, but their name matches are different, and they did not give any 'half' stuff.

[familydar]

Half means just one half of a couple is shared.  For instance if your grandfather married twice and had children by both wives, and those children went on to have children themselves, his grandchildren through his first wife would be half first cousins to his grandchildren through his second wife.  The once removed bit is to do with generational difference.

Jane :-)

[Biggles50]

A Second Cousin will share a pair of Great Grandparents with you.

A Half Second Cousin will share One Great Grandparent.

A 2C1R would be a child of your Second Cousin.

Do note that what these websites offer is a prediction, not necessarily a factual relationship.

[mlrfn448]

Many Thanks for your replies.
of course, I knew what a half sibling is, but had never previously thought it woud apply to other ancestors.
But I realise it is a guess based on the number of shared cMs etc.
I am finding it very interesting.
The one name I recognised is my mother's sister's daughter's daughter (ie a 2nd cousin to my son, whose dna was tested, which came out at half 3rd cousin. The interesting thing though, are the names which came out higher, and which I do not recognise, so will have to work on finding out who they are, and how they are related.

[Biggles50]

Many Thanks for your replies.
of course, I knew what a half sibling is, but had never previously thought it woud apply to other ancestors.
But I realise it is a guess based on the number of shared cMs etc.
I am finding it very interesting.
The one name I recognised is my mother's sister's daughter's daughter (ie a 2nd cousin to my son, whose dna was tested, which came out at half 3rd cousin. The interesting thing though, are the names which came out higher, and which I do not recognise, so will have to work on finding out who they are, and how they are related.

You are right there, Ancestry’s predictions are based on the data that they have.

Every time we link a DNA match into our tree and then use the “Edit Relationship” feature, we give Ancestry the data to add to their database as to what cM actually relates to which Relationship.

Hence why we often get “2C1R to 3C” etc predictions.

[Glen in Tinsel Kni]

Be grateful it's not a My Heritage prediction, by default they show full relationships which leads to the predictions being the wrong generation.  It is possible to see the half relationship options but they have to be selected manually.

I only have half relatives as both my parents are NPE cases and at least one grandparent is too. I have to go the extra step with every single match on MH and it's getting very tiresome. 

[4b2]

I only have half relatives as both my parents are NPE cases and at least one grandparent is too. I have to go the extra step with every single match on MH and it's getting very tiresome.

Have you solved any of the cases?