DNA - benefit of getting parent to test as well?

[Turkeyhen]

My half sister and I have both done our DNA via Ancestry recently and I'm wondering if getting our mum to do it as well would give us a more detailed picture. Presumably the more family members that do it the better but I'm not sure how it all works tbh. It's fascinating to see the differences between our results on the maternal side (eg I have Irish where sister has none). I realise it's all very imprecise!

Yes do it! the further back with your generations you can test the more information that you will find.

I mentioned something about this on a thread just a couple of days ago (which is why I've got the figures to hand).

My mum has 20,000 matches on Ancestry, my dad has 18,000 and I have 16,000 matches.

Of those 16,000 matches, Ancestry says that about 9,000 are on my mum's side and 7,000 are on my dad's side.

So since my mum has 20,000 matches that means that I've gained an extra 11,000 matches on her side (20k - 9k = 11k).

My parents have 38,000 matches between them so, in my case, the number of matches more than doubles by going back one generation.

"...but I'm not sure how it all works tbh."

50% of your DNA comes from your mum and 50% from your dad, and the same with your half-sister except that 50% comes from her dad.

The 50% you each get from your mum is not going to necessarily be the same - it's totally random.

There's a very good (and simple) explanation of how it works from Ancestry here with an easy example:

https://support.ancestry.co.uk/s/article/Understanding-Inheritance

"(eg I have Irish where sister has none)"

How Ancestry works is that they compare each section of your DNA to people whose ancestors have lived in each area for a very long time and then add up how many sections are most like those people from each area.

That's how you get eg 70% England & Northwest Europe.

But you didn't inherit exactly the same DNA from your mum as your half sister did so, especially if you only have a small amount of DNA from one area, then it is very possible that you inherited different DNA.

I will give you an example. My mum is the following:

England & Northwest Europe 79%
Wales 9%
Scotland 6%
Norway 4%
Germanic Europe 2%

My dad is:

England & Northwest Europe 69%
Wales 20%
Scotland 8%
Norway 2%
Ireland 1%

My dna is

England & Northwest Europe 74%
Wales 16%
Scotland 10%

So I have none of the Norway, Ireland or Germanic Europe that either of my parents have as I simply didn't inherit that DNA.

It may well be that if my sibling did a dna test that the Irish and Norwegian dna would show up in them - it's entirely random which bits you each inherit from which parent.

Potentially useful.... I have a 3rd cousin, "Dave". We corresponded & collaborated for years. Later, My daughter & Dave ended up on Ancestry.com : their DNA didn't come up as particularly matching (OMG).

My dad's identical twin tested... uncle matches well with Dave (phew).

Dave's nice, glad to know we are related after all, lol.

@Another2Cats thank you for taking the time to explain, that is very helpful

I understand the principle that we get 50% from each parent and that siblings won't get the same combination of dna from a parent. What I don't really understand is how getting parents to do their DNA will impact on our results - it's amazing that you got thousands more matches (has this led to any breakthroughs for you?), did your ethnicity profile stay the same or did your parents' DNA tests change it in any way?

My mum has agreed to do hers but unfortunately I can't get my father's, which is a shame because I have a brick wall on the paternal side I would love to break down. Disappointingly I haven't got any matches that look helpful with that particular ancestor (great great grandfather).

I realise the ethnicity profiles are changeable as the DNA database grows so it's not to be taken as written in stone. I have this unexpected Irish on the maternal side but we have no known Irish ancestors through our mother - however we have Scottish ancestors and I wonder if the Irish ethnicity is from them ie generic Celtic. Looking at the Chromosome Painter my maternal side chromosome 1 is entirely Irish (Ancestry suggests long blocks of one colour tend to suggest relatively recent ancestors in that area). Is this a clue for further investigation to find Irish ancestors or should it be taken with large pinch of salt as this is a beta feature on Ancestry?

I clearly have a lot to learn - currently feel like I'm blundering about in a fog of ignorance 🥴

@YeOldeTrout oh that does illustrate how getting parents (or their identical twin) to test can help!

Sorry for my excessive ramblings but I'm wondering how on earth Ancestry are able to split your DNA result into parent 1 and parent 2 without parents having tested. If my mum does her test I'm assuming the maternal side profile would be more reliable than whatever sorcery they currently use to determine what came from whom.

"What I don't really understand is how getting parents to do their DNA will impact on our results - it's amazing that you got thousands more matches (has this led to any breakthroughs for you?)"

The main impact is that you get matches with people who are more distantly related and so this can confirm your family tree back to an earlier common DNA ancestor than you could with just your DNA. It can also help to clear up matches where Ancestry can't tell you which side of the family the match is from.

"has this led to any breakthroughs for you?"

Yes, quite a few. I'll just give a couple of examples (with made up names). Sorry if this is too much detail but I probably need to explain the background for it to make sense.

Around 1760 a Mary Jones, daughter of Thomas and Mary is born in a village. At about the same time in a nearby village another girl with the same name, Mary Jones, the daughter of James and Margaret is also born.

Then about twenty years later one of these Mary Jones gets married in another village close by to these other two villages. That Mary Jones is my ancestor, but which one is she? Unfortunately Mary Jones is a very common name.

Prior to 1837, the name of the father was not recorded for marriages so it's just Mary Jones of this parish married XXX.

The first thing to do is to see if there are any records of a Mary Jones having died or of another Mary Jones also getting married. Failing that, you're rather stuck if there is no DNA evidence.

There was no one who I was a DNA match with who was related to either of the Mary Jones. But then when my dad did a DNA test I found three in particular that matched with him as 5th-8th cousins (they turned out to be 6th cousins of my dad) and when I traced their family trees they all linked back to other children of James & Margaret but not Thomas & Mary - the other names weren't quite so common so it was easier to identify them.

So I then knew that it was the Mary who was the daughter of James & Margaret who was my ancestor and not the other Mary.

There have been quite a few situations like that.

When I first started out there was one much nearer to home. There was a woman who was in the USA who was listed as my 2nd-3rd cousin but no side of the family was given (it was "unassigned") as Ancestry couldn't work out which side of the family the link was on.

When my parents did their DNA tests it turned out that she was a close relation of my mum but a much more distant relation of my dad.

It turned out that we were half second cousins (her grandmother and my grandmother were half sisters, same father but different mothers). It turned out that her grandmother had married a US soldier in 1944 and emigrated to the USA after the war.

Up until then I was totally unaware that my grandmother had half siblings and step siblings (my mum didn't know this either). My great grandmother died young and then my great grandfather remarried a widow who also had children. They went on to have more children together.

When I mentioned this to my mum she knew nothing about it and was really surprised to find out. Although she did say that her step grandmother never did like my mum's mother (who was the step daughter) and treated the younger children who were her own much better. It seems like the old trope of the "evil step mother" was playing out here.

Where my dad comes into it is that it turns out the step mother was very distantly related to my dad with a connection going back to people born in the 1690s so they are 7th cousins once removed.

Sorry, yet another huge post, but I think I needed to include the detail for it to make sense.

Basically, they see who your different bits of DNA matches with and they already know a lot about which people are related to which other people.

So what they do is look for all your DNA that matches to one group of people and all the DNA that matches to a different group of people.

The DNA that matches one group of people is likely to all come from one of your parents and the DNA that matches the other group of people will have come from your other parent.

There can be problems though when you come from an area where there is a lot of intermarrying between the same few families as that can confuse things.

See here for an explanation of how they do it:

https://support.ancestry.com/s/article/SideView-Technology?language=en_US

"If my mum does her test I'm assuming the maternal side profile would be more reliable than whatever sorcery they currently use to determine what came from whom."

Yes, although they will also use the same process for looking at your mum's parents (your maternal grandparents)

Thanks so much @Another2Cats