Ancestry DNA tests.


I have family from all over the world, including a white Grandmother born in India from white English parents, she then moved to South Africa where she had my mother, who immigrated to Australia where she had me.
I can’t think of a logical reason a DNA test would actually reveal that-

I’m under the impression that this is just a glorified melanin gene tracker? How would a DNA test be able to determine ancestry at all, considering that we kinda just put lines on a map and said that made them unique? How does the dirt around you effect the dna in a traceable way? And if they can’t, what do they actually do and what’s the point of them?

In: 5

The test tracks specific mutations that are most common in certain areas.

For example one gene is mostly found in central europe, if you have that gene at least a part of your heritage is likely to stem from that population. (The mutation happened there, and spread locally but hasn’t reached other populations in a large quantity yet)

It can’t track where your family was, it can only track where the source material came from, and that only with a limited precision. The percentage values are pretty much guessed.

If your family is entirely european, moved to all around the world but never married any locals then it would say 100% european most likely. (Though people intermixed a lot, so that scenario is very unlikely)

>considering that we kinda just put lines on a map and said that made them unique?

In the past people moved much less than today. The genetic exchange between for example europe and east asia was pretty close to zero before colonization. The test can’t reliably tell you if your family was in france or germany, but it can tell you if it was in france or japan.

They go by matches against the profiles of local populations, so the more data they have the better the match. For instance, much of my ancestry came from Ireland, and the test matched not just for Ireland but for the local area most of my lot came from. They have lots of data for Ireland. Matches for other areas of my ancestry were more general – Scandinavia as a whole for one chunk, West Africa for another bit (part-black great-grandmother) and so on.

One issue with this is that the matches are compared to current populations. Most of the movement of the last two centuries has been from a few areas (Europe, China, India). As you go further back you need a different technique, as repeated small very-long-distance movements bleed genetically into local populations, altering the profile.

The way it works is that these companies only look at a handful of genes that tend to vary with different groups of people, and then they compare your results to their own reference database of people from some region to see if it matches. This works because discrete populations tend to have similar genetic mutations because for most of human history until very recently, people never traveled very far and mostly reproduced with other people nearby. In other words, People from the Arabian peninsula for example never really traveled to Ireland or southeast Asia or whatever to reproduce, so all of those mutations remained in the roughly the same populations of people.

It’s also important to remember that these tests aren’t telling the nationality of your ancestors – there’s no way to conclusively prove that, it’s simply telling you what area of the world your ancestors were *most* *likely* from. So for your facts, an ancestry test won’t know that your grandmother was born in India, it will just say she has DNA mutations consistent with people born in Britain. And your ancestry test may or may not include results from South Africa or Australia depending on whether or not your grandfather and father were from there. If your family is all of English descent, your test will say they regardless of where people lived.

These tests also aren’t particularly accurate for a number of reasons, but that’s a different issue.

A DNA test wouldn’t be able to tell you that your grandmother was born in India, or that your mother lived in South Africa. How it works is that there are certain genes (generally not associated with a certain visible thing like melanin) that is very common in a specific location.

For example, if you have a sequence in your DNA, let’s call this sequence ABC, and you live in Kerala, India. If we sequence a million Kerelans, we find that only 0.05 % of people have ABC. On the other hand, if we sequence a million Greeks and we find that something like 20% of Greeks have ABC, there’s a strong possibility that ABC gene originated in Greece, and that you got it from a Greek ancestor.

Why do Greeks have it and not Keralans? At some point, hundreds or thousands of years ago, a random mutation happened in some Greek dude. It affected absolutely nothing, his hair didn’t change colour, he didn’t get shorter, nothing. It did not prevent him from getting married and having a kid. So he did, some of his kids all had ABC. Then their kids had some ABC. And so on and so on. Slowly, a large amount of the population has ABC.

People back then didn’t have airplanes, travelling far took very very long and was very dangerous. Really the only way to travel for long times was to be an explorer or a soldier. So the Greek dudes descendents generally stayed around Greece.

Maybe one soldier joined Alexander’s campaign and married an Indian woman, creating a small population of people with ABC. Maybe a Greek woman was captured as a slave by slave traders and ended up escaping to Kerala where she got married and had kids with ABC.

So we could say, despite living in India, being born in India, looking “Indian,” you would carry ABC hidden in your genes giving evidence that you have some Greek ancestry.