> Techniques used to read DNA only read short segments, from which larger segments are inferred. I think you’re describing short-read sequencing here but this

> Techniques used to read DNA only read short segments, from which larger segments are inferred. I think you’re describing short-read sequencing here but this isn’t what any of these services does. They do microarray genotyping rather than sequencing. And in neither case is there “inference”. True there’s something called imputation but it works quite differently and I don’t think (though I don’t know) that 23andme uses it for ancestry. I’m also not sure what you mean by “bijection” in this context.