Some folks DNA related to me but not my cousin who also took a test

[Alan of Kaslo]

Hello.

I had some really good luck getting my DNA done. First thing I found was a very close relative that turned out to be a first cousin. Turns out our mothers were sisters and the lifelong mystery of who was her father was solved. That opened up a big part of my mother's family tree which was nice.

On my father's side ... the man on his mother's birth certificate had actually been dead 10 years before her birth. Her real father was another complete mystery. Nothing really popped out on the DNA match screen the way it had on my mother's side.

My 2nd cousin ... the son of my my father's sister's daughter ... took the same type ancestry DNA test. I see him top of the list as a match. I use him to compare to potential matches that I have.

Here's my question. I noticed at a certain point if you go back he will not show up as co-related to people who are related on my father's side. I believe it takes going back 7 generations and then this cousin does not show up in my thru-lines.

I found what a bunch of clues that seem to point to an individual on the DNA match screen being a relative of the man who fathered my grandmother. But ... my cousin does not show as DNA-related to this person. I count the generations between this person and the potential parent and it's 4 (after him the potential parent is the 4th).

I'm wondering if the 4 generations plus the fact that i'm comparing to my father's sister's grandchild would have a water-down effect? Making it so he might not show up as co-related.

Sorry for explaining it so bad.

Any help greatly appreciated!

Thanks.

[Biggles50]

It is very possible, DNA is not inherited in a predetermined order but by a random process called Recombination.

By going back four generations it is very possible that from that Ancestor you (or any Cousin) inherit no DNA.

Your Ancestry test did not analyse your whole DNA, just about 7% so you should see how variances can happen.

At 3x GGP level with equal DNA inheritance you will only have c3% of that 3xGGP’s DNA.

As an example I have a 364cM match and yet two of their first Cousins each share 115 & 95cM respectively with me, such is the randomness of DNA inheritance.

[Alan of Kaslo]

Thanks. That was helpful.

I won't automatically disregard this person just because my cousin is not showing as related to them. I was ready to do that before making this post.

The person i'm curious about tests in at about 40cm and another known cousin has 32cm. This cousin is the great grandson of my great grandmothers brother. But now that i have learned from you about the randomness of how the DNA is passed down I don't think it's as easy to compare as I had thought.

Thanks again

[dublin1850]

I heard it described once as a stew. We all have a bowl, but I have a bit more beef than carrots, you have more celery than beef and sister Mary is the only one got mushrooms, but we all got our stew from the same pot.

[BushInn1746]

It is very possible, DNA is not inherited in a predetermined order but by a random process called Recombination.

By going back four generations it is very possible that from that Ancestor you (or any Cousin) inherit no DNA.

Your Ancestry test did not analyse your whole DNA, just about 7% so you should see how variances can happen.

At 3x GGP level with equal DNA inheritance you will only have c3% of that 3xGGP’s DNA.

As an example I have a 364cM match and yet two of their first Cousins each share 115 & 95cM respectively with me, such is the randomness of DNA inheritance.

I know virtually nothing about DNA, except that I am told I looked like my late Mum and the family Dentist said our teeth looked similar, etc.

US National Library of Medicine
Recombination

https://www.ncbi.nlm.nih.gov/books/NBK26898/

[Biggles50]

I saw this image in an article which shows how random DNA inheritance can be.

[Glen in Tinsel Kni]

Unknown parentage, half cousin relationships and big age gaps in a generation can cause some really odd looking results at times. I've had a few in the last couple of weeks in the 20-30cM range suggested as 4-6 cousins but I'm pretty sure their grandparent has also tested and is my half 2c.  It all fits according to bmd, they read but won't reply to messages and confirm the grandparent theory or shared cM to others. It's either another dead end or a case of me going it alone buying certs and diving into their social media. 

[brigidmac]

Biggles that's a great image id like to copy it

Alan when you say your 2nd cousin doesn't show as a match do you mean he doesn't show as a shared match

I manage my.mothers my paternal.aunt's  and nephews DNA results sometimes the distance matches ( usually under 20cm) too small to show on shared matches

But if I go into their individual accounts the person does actually show as a match

Another Example   I looked at my.mothers shared matches to a Welsh relative my nephew didn't show on her shared matches
But when I compared my nephew's results to the person not only did he match 25cm bot on his shared matches my mother+ myself showed up

Occasionally a younger generation gets a higher match.

[Alan of Kaslo]

My cousin shows up fine as connected to me.

This cousin is grandson to my Dad's sister. So right away he is watered down a bit. The person I was trying to compare DNA with was about 4 generations back. I'm related 40 cm's to this person's relative  but my cousin doesn't show up as co-related. Before I made thread I had assumed any potential father to my father's mother would have to be related to my 2nd cousin... which is a wrong assumption, apparently.

The thing I kept forgetting beyond this new info is the fact that this cousin is through my Dad's sister and from a daughter of hers even. That has to have some diminishing effect on DNA you would think.