Genetic ancestry query

[Dauphin]

You have 23 chromosomes from each parent. There is a 1 in around 4 million chance you get all your paternal chromosomes from one or other of your paternal grandparents. Repeat for the maternal size and there is a 1 in around 2 million chance you have no inherited chromosomes from one of your grandparents. Is this right, or does genetic recombination make this analysis meaningless?

Go back further and the chance of sharing any inherited chromosomes with an ancestor tends to zero very quickly.

So. How hollow is genetic ancestry testing? Either for the above (potentially flawed) or other reasons.

[Ben Kenobi]

How hollow is genetic ancestry testing? Either for the above (potentially flawed) or other reasons

Well, if you do the math you can show the percentages. 1 in 2 million will work out to be 1 in 2 chance, or about a 50 percent chance of inheriting no genes from an ancestor 20 generations back. That's some 600 years. Most people can't go back that far.

That being said - that's just one ancestor out of roughly 1 million ancestors. The reason it becomes significant is because not all of us have perfect trees. At that point our trees will start to loop in, meaning that certain ancestors will have a much greater contribution than others.

Then there's the difference between one ancestor and your entire ancestry. Something that is not true in part can be true in aggregate.

[Dauphin]

You only have 23 pairs of chromosomes. Setting aside recombination, go back just a six generations (64 ancestors) and you have a 1 in 1 chance of no chromosomes from at least 18 ancestors.

[Proteus_MST]

More interesting is the mtDNA ... the DNA in the Mitochondriae, as this only comes only from the mother (as only the Mitochondriae in the Oocyte form the base for all Mitochondriae you have in the cells of your body)

That`s usually the DNA that is used when you try to find out about migration movements of the Homo sapiens (and was also the DNA that was used to determine that the matrilineal Eve came from Africa)

[ricketyclik]

Go back further and the chance of sharing any inherited chromosomes with an ancestor tends to zero very quickly.

So I didn't inherit any of my chromosomes from anybody further back than a few generations? Suddenly the bible makes sense.

[Jon Miller]

You only have 23 pairs of chromosomes. Setting aside recombination, go back just a six generations (64 ancestors) and you have a 1 in 1 chance of no chromosomes from at least 18 ancestors.

My understanding that the real genetics is more complicated then that. For an example that has already been referred to see mDNA.


JM

[Dauphin]

So I didn't inherit any of my chromosomes from anybody further back than a few generations? Suddenly the bible makes sense.

Flippant I know - but it's that certain ancestors have more input than others, and any given ancestor is unlikely to have contributed much of anything to you. It's a variant thought of genetic drift.

[Uncle Sparky]

... still trying to rationalize why you're children look like your Armenian butcher?

[giblets]

You only have 23 pairs of chromosomes. Setting aside recombination, go back just a six generations (64 ancestors) and you have a 1 in 1 chance of no chromosomes from at least 18 ancestors.

[ricketyclik]

I find it amusing too, but I think of genetics along the lines of diffusion (every glass of water we drink has some molecules of Archimedes' urine in it). Perhaps that's wrong-headed

[Dauphin]

Mixing is aided by recombination. My comment was in extremis.

Recombination apparently occurs on average once per chromosome per generation. If it doesn't recombine in any given generation you only get genes from one side of the family passed on in that chromosome. Your mother's or father's 'ancestry' for that chromosome is excluded when passed on by you.

[BeBMan]

I'm not sure why the op assumes I got 23 parents?

*hides*