How Do DNA Ancestry Tests Work? How 23andme Works.


You’ve probably seen the ads for them. Spit in a test tube, send it a company such
as 23andMe or Ancestry.com and in return you’ll find out what your genetic ethnicity is, with
you being able to see if your ancestors came from regions such as Europe, East Asia or
Sub-Saharan Africa for example. In 2018 alone, people taking DNA ancestry
tests exceeded that of all previous years combined, with 26 million people sending their
DNA to companies such as 23andme and Ancestry.com. 100 million people are estimated to analyse
their ancestral background in the next two years through such DNA ancestry services – so
how are these companies analysing your ancestral history from your spit? DNA is made up of two coils which wrap around
each other to form a double helix. Our DNA is made up of molecules called nucleotides
which contain a phosphate group, a sugar group and a nitrogen base. It is the nitrogen part which determines our
genetic code, with there being four types, A (adenine), T (thymine), G (guanine) and
C (cytosine). DNA in humans is 99.5 percent the same across
all of us, which means that these DNA genetic ethnicity tests are looking at the remaining
.5% (which is about 600,000 of the 3 billion bases in our DNA). Single nucleotide polymorphisms, or SNPs are
the most common type of generic variation between us. An example of differences in DNA is that you
may have a nucleotide of thymine (T) in a certain stretch of DNA whereas someone else
has a cytosine (C) nucleotide. These SNPs are passed down between generations,
which means the more SNPs you have in common with someone the more likely it is you share
a similar and more recent ancestry, Services which as 23andme and Ancestry.com
compare your SNPs to a reference population of their own. 23andme for example has 11,091 people who
they have chosen to be their apart of their reference dataset. The likes of 23andme compare your SNPs to
SNPs in their reference populations which are categorized by locations in which those
SNPs are common across their dataset. 23andme for example looks at your SNPs compared
to 45 reference populations to see which segments of your DNA closely matches that of the different
segments in their 45 reference populations, and then assigns that ancestry to the corresponding
segment of your DNA. They then do this for all the individual segments,
add them together and compute your overall ancestry composition. An example is the maternal haplogroup H, which
as you can see in this worldwide distribution graph is very common to Europe but is rare
to those native to Australia or the America’s. This means if you have this specific marker,
there is a decent chance that you have at least one European ancestor who has passed
this on. Obviously using just one DNA marker isn’t
very useful, but this sort of technique is used across hundreds of thousands of DNA markers
using reference populations to see what markers are more common in different populations. There are a few downsides to how the likes
of 23andme and Ancestry.com do these genetic ethnicity tests. Reference groups are for the most part people
self-reporting their ancestry, meaning there is a chance of error there. There is also not a consistent amount of people
in reference populations across the world. There are not many African people in their
reference populations, compared to the likes of Europe which has a much larger reference
population, which means some results may not show up in your results, or not be very precise,
due to there just not being enough data to properly pin point – but these services
have been greatly increasing their reference populations in all areas in the past few years. This means that your results over time will
change, due to more people being added into the dataset meaning there are more SNPs to
compare you to. All these services such as 23andme and Ancestry.com
are also using different datasets, which means you could get different results between the
two services. Some people have seen one of them report they
are 9% Greek for example, while the other reports 28%, which is a fairly large difference. There is also the discussion on privacy, with
us sending our DNA to private companies in which they could use how they want – but
that is a fairly long discussion. Thanks for watching and be sure to subscribe.

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