Why do I need to complete the Ancestry Questionnaire?

Why should you complete the ancestry questionnaire? After all, we’re analyzing your DNA, so shouldn’t we be able to determine your ancestry without additional input?

It’s a great question, and we’re happy to explain what’s going on.

Your input helps us properly assign your DNA to your mother’s and father’s chromosomes. When your DNA is read, what you get back is two reads for each position (e.g. AA, AT, GT etc.). One of them belongs to the chromosome you inherited from your mother, the other one to the chromosome you inherited from your father. However, without also having your parents’ DNA available, it’s really hard to tell which read came from which parent. Algorithms help us get part-way there, but even with the leading industry algorithms, we end up with chromosomes that are mosaics of your parents DNA. Now, this may not affect you much if your parents are of the same ethnicity. However if you are admixed (e.g. Chinese and Italian), you may end up with scrambled chromosomes, which will decrease the accuracy of both our ancestry model and our PRS models.

By filling out the ancestry questionnaire, you’re helping us sort different chunks of your DNA to your maternal and paternal chromosomes. Your answers don’t affect what each of those chunks get called in our ancestry algorithm — we call these chunks first, and we do so by comparing each piece of your DNA with 33 different populations that we have in our database. However, it may affect the final layer of the ancestry algorithm that looks at all your chromosomes in entirety — this layer works better when most of the DNA pieces are on the right chromosome.

Further, our ancestry algorithm is by no means limited to your grandparents, which is the information we gather. It reflects hundreds of years of ancestry. For example, you may think that all your grandparents are Hungarian, but our ancestry algorithm may detect significant Ashkenazi Jewish ancestry, that you may or may not have been aware of. This happens.

Finally, we use this information to adjust our PRS models. For example, when we predict your risk of heart disease, we use reference DNA of your ethnicity to adjust your risk score. Therefore, by completing the ancestry questionnaire, you’re helping us to provide you with the most accurate and personalized analysis of your DNA. (edited)

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