How can genetic relatives be related to both maternal and paternal sides, but not each other?

Question

I am completely ignorant to all of the genetics of ancestry, although I have a keen interest in family history. I did a DNA test through 23andme, as did my mother and a paternal aunt. In my list of DNA relatives I noticed that there are at least 4 people who are genetically related to me, my mom and my paternal aunt. These 4 people are not genetically related to each other. Nor is my paternal aunt related to my mom. How can this be?

Additionally, a different person that I am genetically related to (we may share 3rd great grandparents) does not appear to be genetically related to my mom or my paternal aunt.

Could someone please explain this to me in layman's terms?

Answer 1

It really is very simple.

Everyone has two pairs of grandparents and 4 pairs of great grandparents and 8 pairs of great great grandparents.

First cousins share a pair of grandparents. Second cousins share a pair of great grandparents. Third cousins share a pair of great great grandparents.

The 4 people could be a third cousin of, for example, your Mom's 2nd, 5th, 6th and 8th pair of great great grandparents. If that is the case, then they need not be related to each other.

The same can be happening on your paternal aunt's side where the 4 people could be a third cousin of your aunt through her 1st, 2nd, 5th and 7th pairs of great great grandparents. They again need not be related to each other.

These 4 people can be further than 3rd cousins, and if so, they'll have even more of your ancestral lines to differentiate them.

With regards to the additional person related to you, there are two possibilities.

1. Either she's related on your Dad's side and your Dad happened to get a lot more shared DNA, most of which he passed down to you, than his sister (your aunt) got. Your aunt might have just got under the threshold to be a match, or

2. You could be related on both your Dad and Mom's side. Both your Dad and Mom passed down shared DNA to you. Neither your Dad (or aunt) or Mom has enough shared to reach the threshold that is considered to be a match. But the combined amount you received was enough and was called a match.

Answer 2

I ordered 3 kits. One for me one for my oldest daughter and one from my neice(sister's daughter) Let me break this all the way down so there is no confusion.

My mother was married 2 times. 1st marriage produced my sister (kim) 2nd marriage produced me.

We will call my mom's 1st husband(not my dad but my sister's (kim)dad) Ed. We will call 2nd husband Bob (my Dad not my sister's (kim)dad)

Ed who is my sister's father also had a so from another relationship with a woman we will call Jill. We will call Ed and Jill's son Ron.

My mom and bob produced me I grow up I meet Ron so Ron and I get married and we have Ann.

*remember Ron's Mom is Jill and his Dad is Ed. Ed is my sister's(kim) dad but ed isn't my Dad.

Ed who is my sister's dad is also Ron's dad. My sister(kim) and my husband Ron have the same Dad but not the same mom. Im a sister to kim Ron is a brother to Kim. But ron is not my brother.

Kim has a daughter mia i have a daughter ann

Mia and ann have a dna test Ann my daughter and mia are 1st cousins

Mia is anns cousin on her mothers(me) side and on dads side(ed) So in a nutshell my mom was married her husband cheated he had a son from another woman.

She divorced him and married my dad I grew up her now ex and other womans son grows up We get married my husband and i have the same sister my husband and my sister have the same dad but not the same mom