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I basically took a 23andme test and found out genetically I was 1% African. The weird part though is that family records shows that my father's mother's grandmother was African, making me 1/16 African. Shouldn't it be closer to 6%?

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  • $\begingroup$ hi Ray. Nice question. I would suggest you think about some additional question (and maybe 23andme explains it or you might have to search internet). For example, what doe it mean to be 1% African? Technically, all people are from what is currently known as Africa. Also, for example, a lot of people from South Africa have predominantly European ancestry. Finally, when someone says 1%, what is the uncertainty of this number? There is no precise measurement in science, it is always 15.5±0.3 or something $\endgroup$ – Oct18 is day of silence on SE Nov 28 '18 at 17:12
  • $\begingroup$ it's a bit like shuffling 16 packs of cards into 1 as far as I know... That should have a quantitative answer giving the probability of having less than 50% of a parents, less than 25% of a grandparents and less than 6% of a great great GP's genes. After 4 generations I expect there's a 20% chance that one grandparent has only 1% of genes in an offspring. $\endgroup$ – com.prehensible Dec 2 '18 at 8:01
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The science behind "being X % from a certain place" based on genetic analyses is... approximative at best. It relies on the assumption that some genetic traits are only found in certain (narrow) regions of the planet - which for most of them, is not really true.

Additionally, did your test provide any confidence metric for this result? If not, it may mean that it may be derived from a statistically unsignificant number of traits (and the number could therefore mean anything) or maybe it's simply something like 1% with a confidence interval of several points, in which case the result could be a compatibe the mathematical truth. Genomes are large and have complex dynamics, it it probably difficult to get a precise estimate.

On a side note, there is more genetic diversity in native African populations than on any other continent (for reasons pertaining to Homo sapiens history) so "African" does not describe a homogeneous population.

Source: https://www.nature.com/articles/nature13997 doi:10.1038/nature13997

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