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Conversation with Francesc Calafell. Part 2

Francesc Calafell, associate professor at Pompeu Fabra University
So, we always share our mitochondrial DNA exactly with our mother? No, because if that were the case, then everyone would have exactly the same mitochondrial DNA and we have differences due to mutation. In a small fraction of the cases there are mutations –usually no more than one or two– if you compare a mother and a child. And for the Y chromosome which is much bigger? Yes, then you would find many more private mutations along the Y chromosome and for a subset of the Short Tandem Repeats, the rapidly mutated, the Short Tandem Repeats, you would certainly if you have a few of them you would find differences between a father and his sons.
And if we go back in time, can we go very, very far back in time to look for the ancestrality of our mitochondrial or Y chromosomes genomes? Certainly, we can use the mitochondrial DNA and the Y chromosome to place humans in the tree of life. That’s the case for humans and for any other species. It’s a tool actually, it uses a routine to identify the species of origin of a given, of an unknown sample. For example, would you differentiate very easily the mitochondrial DNA or the Y chromosome from us from those of these gorillas here? Certainly, there are a number of differences and it would be quite easy to. And the ancestrality in humans what do they tell us?
We were talking about this accumulation of mutations. It happens in time, but it also happens in space. The families tend to stay roughly in the same area and this means that the mutations and the differences that accumulate tend also to differentiate geographical populations. So, there are types of Y chromosomes and mitochondrial DNAs that are very particular of some populations and here population can be from a subcontinent to a whole continent. There are types of Y chromosomes that are for instance particular of the Iberian Peninsula, we find them here, we find them rarely elsewhere in Europe, we find types of Y chromosomes that are very particular to say in northern Africa and so on and so forth.
And if you go back in time this comes to the concept, strange concept, of mitochondrial Eve for humans, what’s the meaning of that? Of course, if we go back in time our mothers would converge to some sort of universal mother, but that doesn’t mean that she was the only woman living at any particular time. And if we think of our own genealogies you and I could share an ancestor say 10 generations back in some branch of our genealogy but in another branch, it could be a hundred or a thousand generations ago that we share the ancestor. So, the idea of this ancestor, when and where it lived?
It’s a matter of debate because to know that, you have to be very precise about mutation rates. But the consensus right now is that for mitochondrial Eve lived about 150 thousand years ago in eastern Africa. That means that the human origins is in Africa? No, it doesn’t. It just means that the mother who’s the maternal ancestral to us all lived then and there. We may have other ancestress living in other places in different times.
Francesc Calafell, associate professor at Pompeu Fabra University and principal investigator at the Institute of Evolutionary Biology in Barcelona.

We will discuss the study of genomes, focusing in particular on a tiny but extremely interesting part of them called uniparental markers.

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