How much DNA do you share with your great great great grandparents?

[JennyWr3n]

Just that really! If any at all

How do you mean?

You could work out how much the average person shares with their g-g-g grandparents, but it'll vary for each person, surely? And how would we know?

I suppose I'm thinking about .. if you consider you have inherited 50% your mothers genes and likewise your father, does it then dilute equally to your grandparents and so on and so forth

Yes, in theory, it dilutes equally to your grandparents.

So take your mum's line back to great-great-great granny.

You have 50% of mum's genes.

She has 50% of her mum's genes, so you have 25% of granny's genes.

Granny has 50% of her mum's genes, so you have 12.5% of great-granny's genes.

Etc. etc.

You have 6.25% of great-great granny's genes.

You have 3.125% of great-great-great granny's genes.

Now I hope I've got my arithmetic right and haven't shamed myself.

I thought it was more complicated than below, bcause genes are dominant from one parent over other, you rarely get a true 50% expressed from each. But otherwise...
parents each 50%
Gparents 25%
G-gparents 12.5%
GG... 5.75%
GGG-parents < 3%.
That's pretty small!

You got it right, Sarah, I made a mistake! But still, about 3%.

Thanks! I thought I was in the ballpark but knew it couldn't be as simple as just dividing it due to dormant genes etc.

Fascinating stuff though.

Isn't it fascinating?

I wonder as well how much overlap there must be - less nowadays, I suppose, but when you think about Victorian families living in small towns and villages, it seems quite likely your great-great-great grandparents would include some blood relations already.

Have you found a famous relative on ancestry or something?

It really is.

I've been trawling through my ancestry recently and managed to make it back to about 1780 so far and it got me thinking just how much 'in common' I might share with my 4th great grandma, Mary.

It's 1/16th which is 3.125%.

Sadly no one famous! I've not discovered a link to Napoleon or anything

No it’s not 3%.
It’s 1 in 256 0r 0.04%

You inherit about 6.2% from your gr gr gr grands.
Each line doubles with people and halves with % of DNA

You have the DNA from great great granny's mitochondria as they are passed down the female line. They contain a very small amount of DNA compared to that in the nucleus.

@streamlinedcaverns is correct.

Parents 50%
Grandparents 25%
Great Grandparents 12.5%
Great Great Grandparents 6.25%
Great great great grandparents 3.125%.

What is more interesting is siblings - where is could be anything from 0% (opposite sex siblings only) to 100% (same sex siblings only). On average 50% though.

At Xmas we got together with my mum’s side of the family. My kids have each other, a first cousin (who in average they share 25% DNA with) and a second cousin (who on average they share just 12.5% DNA with). And they all look exactly the same. It’s a bit freaky......

I wonder as well how much overlap there must be - less nowadays, I suppose, but when you think about Victorian families living in small towns and villages, it seems quite likely your great-great-great grandparents would include some blood relations already.

I'm Romany my DNA is impossible and I had to give up with my tree with the multiple relationships. Centuries of endogamy meaning I have lots of doubles.
I've had top DNA experts assess it from Durham University to North Carolina. I'm nothing special but it appears my DNA is interesting to lots of folks.

Sorry, my maths is rubbish. So unless you are me and your greats come out as uncles, aunts, anything but the right relationship, then yes it's 3.125

I thought it was more complicated as well. I remember reading (probably on here) that you could well share no DNA with your 5th great-grandparents backwards.

@SarahAndQuack

Isn't it fascinating?

I wonder as well how much overlap there must be - less nowadays, I suppose, but when you think about Victorian families living in small towns and villages, it seems quite likely your great-great-great grandparents would include some blood relations already.

I'd think your absolutely right. In small areas people do become inter-related. My Grandparents on one side were distantly related cousins. Ive also come across a couple who had the same middle name with an unusual spelling, they queried it and figured out they shared a set of Great Grandparents.

The Queen and Prince Philip are both descendants of Queen Victoria!

@PlanDeRaccordement, could you explain why?

Interestingly I was trawling ancestry. I am pale blue white British redhead and didn't expect to find anything interesting

My great great grandad was born in Barbados, and black I was astounded, it's been fascinating to go back

Have a look at genetics.thetech.org/ask-a-geneticist/siblings-are-around-fifty-percent-related if you really want to know more. I think it explains why my DCs all have my Celtic colouring (which is usually considered recessive not dominant) when their father has Greek colouring.

What DNA traits are dominant and more likely to transfer over generations. I've felt that we are actually more likely to be like our grandparents dominant side. Like my wife is more physically and mentally intune to her grandmother. On her father's side.

I found that one of my aunts is a fifth cousin of her husband. His family is Welsh and hers from the East Midlands so not close geographically. I also found quite a few cases of pairs of sisters marrying pairs of brothers so making interesting DNA combinations for the cousin children.