That isn't really true though. You aren't some kind of clone of your parents. Imagine that both of your parents sit down at a table. Each one has 100 dominoes in front of them. Each parent will randomly take 50 of their dominoes and put them in the center of the table. Those are your 100 dominoes. It could be that your mother has 20 "scottish" dominoes, but not a single one of those dominoes are in the set given to you. You might look at your mother's dna results and say "I'm 20% scottish!" No you're not. You got zip from the scottish side of the family.

With 23 pairs of chromosomes we have 46 dominoes each (ignoring recombination.) This changes the odds of inheriting none of your mother's Scottish dominoes from 1 in a million (2^20) to 1 in 512 (2^9).

> This changes the odds of inheriting none of your mother's Scottish dominoes from 1 in a million (2^20) to 1 in 512 (2^9).

That may be true for mom, but conservatively, there's between a 1-in-100 and 1-in-20 odds of inheriting none of your father's dominoes.

It's been a while since I've taken high school biology, but the odds should be the same as the mother. Scottish-ness is not something that's limited to the X or Y chromosome.

Mitochondrial DNA will only come from your mother, but I don't think we're talking about that here.

What's the mechanism at play here? Each chromosome pair is one from the father and one from the mother.

> What's the mechanism at play here?

cheating

Right, but unless you get your own results you have no idea how the dice rolled for you (how many other game metaphors can I use?).

What if I don't give a shit about being "20% scottish" and only care about relatives-I-didn't-know-I-had and genetically-heritable-illnesses and my parents' reports were clean?

Half siblings are probably the most interesting “relatives-you-didn’t-know-you-had” you can find! They might show up at any time, and you wouldn’t know without having your own account.

that line of reasoning sort of proves the uselessness of even using 23andMe in the first place

No, all it means is you can't look at someone else's results (even parents or siblings) and think that your results would be the same.

>You might look at your mother's dna results and say "I'm 20% scottish!" No you're not. You got zip from the scottish side of the family.

So then the DNA results themselves are wrong since they're based on exactly this logic, just for your parents...

Therefore making the entire thing completely useless.

No, all it means is you can't look at someone else's results (even parents or siblings) and think that your results would be the same.

It would still provide information about health, since you don't inherit all of your parents' alleles. (For example, if your parents are heterozygous for an allele and you'd like to know your status.)

Because you can have a mutation that your parents don't have?

23&me most like will not help you there as they are only looking for relatively well known mutations and not de-novos. They are basically scanning a few (or less) million variants but there are billions of possible new ones

23andme is pretty useless for getting great information from your DNA. I say this because you can get a much better report by exporting the raw data and then ordering a more detailed report from promethase.

Yes, but if you get a mutation in one of the SNPs they test for, it will show positive even though both parents are negative.