Genetics question

[Dr Jekyll]

How closely do you have to be related to someone in order to have more genetically in common with them than with any random stranger?

I've seen a photo of someone who is almost definitely my third cousin and people tell me there is resemblance. But our common ancestor is my great great grandfather (maybe +- one great on his side), from which I presumably only inherited about 6% of my genes. So I wouldn't expect either of us to look like the ancestor never mind each other.

[Simpo Two]

Well if you're choosing strangers at random they might be more closely related than you think! (random being a funny thing)

But generally I'd say anyone in your tree is going to be closer to you than a 'stranger'.

[Shaolin]

It may be 6% for you and him specifically, but if you both come from the same relatively small gene pool, you'll share many more genes in common. There used to be a programme on the telly where some bloke would go to towns around the UK and describe the typical inhabitants, he would then approach people in the street he thought looked typical of the region and almost invariably they and their family had lived there forever.

There is a surprising amount of inter-relatedness in many of us as moving on from place of birth is still a relatively new fangled idea for many.

[Dr Jekyll]

Simpo Two said:

Well if you're choosing strangers at random they might be more closely related than you think! (random being a funny thing)

But generally I'd say anyone in your tree is going to be closer to you than a 'stranger'.

But even strangers are likely to be in my tree somewhere. Isn't almost every one in Europe supposed to be descended from the Emperor Augustus?

Most people can see a resemblance with their parents, IE a closer resemblance than with the typical stranger. Also with grandparents. But how far back can you go and still expect to see a genuine resemblance?

[Simpo Two]

Well I once ran a club with a someone who looked like a caveman, so quite a long way I'd say.

[rhinochopig]

Dr Jekyll said:

How closely do you have to be related to someone in order to have more genetically in common with them than with any random stranger?

I've seen a photo of someone who is almost definitely my third cousin and people tell me there is resemblance. But our common ancestor is my great great grandfather (maybe +- one great on his side), from which I presumably only inherited about 6% of my genes. So I wouldn't expect either of us to look like the ancestor never mind each other.

Is this a thinly veiled "Would it be ok to rattle my cousin" thread?

[otolith]

May be of interest;

http://www.sciencedaily.com/releases/2004/09/04093...

[dandare]

rhinochopig said:

Is this a thinly veiled "Would it be ok to rattle my cousin" thread?

Is he from the Fens, perhaps?

[Dr Jekyll]

I avoided putting this in the 'things you've already wanted to know the answer to' thread because I thought the science forum might produce more sensible responses.

[Nightmare]

Dr Jekyll said:

But even strangers are likely to be in my tree somewhere. Isn't almost every one in Europe supposed to be descended from the Emperor Augustus?

Most people can see a resemblance with their parents, IE a closer resemblance than with the typical stranger. Also with grandparents. But how far back can you go and still expect to see a genuine resemblance?

It doesnt really work like that though...one of the reasons that 'cracking the genetic code' has turned out to be so frustrating is the realisation that gene coding for everything from physical characteristics to levels of stomach acid produced is covered by multiple genes - and their level of expression varies itself - meaning you end up with huge permutations for almost every aspect. If you managed to get a pic of all your antecedents for the last few hundred years its likely that you'd find someone way back who made you go "wow, they look just like me" The various characteristics which make up your face are more likely to pop in your family tree, but not necessarily from those closer to you....but more likely than a random stranger

[Dr Jekyll]

Nightmare said:

The various characteristics which make up your face are more likely to pop in your family tree, but not necessarily from those closer to you....but more likely than a random stranger

That makes sense, I've got great uncles that look nothing like me, and distant cousins with a resemblance. But there must become a point where someone in my family tree is so far removed that they are no more likely to look like me than a random stranger would.

Googling this topic I found this article.

http://www.dailymail.co.uk/femail/article-1222921/...

It suggests that princess Beatrice looks like Queen Victoria (well maybe). But also that prince William looks like Edward 1st! If he does I reckon it must be coincidence since Edward 1st lived so long ago at least half the country must be descended from him. And probably half the country in 1300 are Williams ancestors so why should he look like the King in particular.

OK resemblances might persist longer with Royals because of the level of inbreeding, but there must be a limit beyond which any resemblance must be coincidental, that's what I'm trying to pin down.

[otolith]

Dr Jekyll said:

OK resemblances might persist longer with Royals because of the level of inbreeding, but there must be a limit beyond which any resemblance must be coincidental, that's what I'm trying to pin down.

Your appearance is the combination of a set of traits of variable heritability and variable variability within the population you are considering. You may have a nose which looks more like your grandad's than your mum or dad's, but I bet your skin colour could be pretty reliably predicted by looking at your parents.

It's no coincidence that Heikki Kovalainen looks more like Mika Hakkinen than Lewis Hamilton or Fernando Alonso - there isn't a sharp cut-off, people who are more genetically alike will tend to look more similar.