Prof Mark Jobling - Genes and genealogy
Kat - In recent years we've seen an explosion in people digging into their family history, tracing their family trees. And with the advent of cheap gene sequencing, there's a new field of recreational genetics springing up, as people try to unpick their genetic ancestry. But what can our genomes actually tell us about where we came from and who we are? Professor Mark Jobling, at the University of Leicester, is a leading expert in human genetics and genealogy, so I asked him for some answers.
Mark - Well, the human species is remarkable for the fact that it covers almost the entire habitable surface of the Earth and has very, very large numbers. But that situation has arisen in a very short time compared to other species. So, it's only about 200,000 years since our species originated. During that time, there's been a migration. We know from various lines of evidence that humans originated in Africa about that time and then migrated into the old world. Thereafter, there were several further migrations. In more recent years, we've had contact between populations that have been separated for very long periods of time.
So, we're interested in looking at modern human genomes, the genetics among human populations and trying to disentangle various aspects of those migration histories. But I guess you could ask, "Well, don't we know a lot of that anyway from history and other sources?" The answer is, we know some things, but not enough. There's also often conflicts between different sources of evidence. So, genetics has something new to bring to try and to understand how we ended up in the way we are.
Kat - And what sort of things you're actually looking at when you talk about the genetics of different populations? What sort of things differ genetically between people?
Mark - Well, the first thing to say is that, people are all very, very similar to each other indeed. That's the important thing to stress. We always talk about the differences, but in fact, we're 0.08% different. We are a very uniform species. So, we focus on the very small number of differences. Beyond that, we look at differences between populations in order to try to understand when particular groups of people move from one place to another.
And so, we might think for example of the migration of the Jewish diaspora. People originated and moved about 2,000 years ago across Europe or the migration of the Roma people - sometimes called gypsies. They originated about 1,000 years ago in northern India and then migrated across Europe. Or more recent events like the transatlantic slave trade which brought African people together with people who've been living for thousands of years in the Americas and with people previously been living in Europe. So, there have been a lot of these complex mixture events and you can look at differences between populations - these very small differences - to try and illuminate those events.
Kat - What sort of things can you tell? What sort of resolution can you get? Can you tell for example that a whole bunch of people all came from one family, one starting person for example?
Mark - Well, it depends which bit of the genome you look at. So, you can look at individual genomes. Good examples are the Y-chromosome which passes from father to son or mitochondrial DNA which passes from mothers to all of their children. So, those form what are called gene genealogies. They're not necessarily referring to genes themselves, but you can look at the pattern. You can form a family tree of all of those sequences in the world and look at the pattern of those in different populations.
So, that has some advantages in that it's rather simple to understand, but some disadvantages because as you said, you're looking in the case of all Y-chromosomes and essentially, one pedigree. So, that all modern Y-chromosomes descend from one single man who lived at some point in the past. Similarly, all mitochondrial DNAs descend from one woman who lived at some point in the past. So, those are only telling us about single ancestors in any one person's actual genealogy. So, there's simplicity there which gives advantages and disadvantages.
So now, we have whole genome methods of trying to understand diversity and that again brings advantages and disadvantages. So, on the one hand, we're looking at the entire genome or 'snips' (SNPs) that are distributed across the genome and that gives us many different evolutionary stories. Almost each snip has a different story to tell. We're looking at the averaging of those and that gives us a kind of a general picture of how populations are related together, but it doesn't tell us about individual ancestry.
Kat - Because that's something that people are very interested in. There's a whole industry of people looking at their family history, their family trees, trying to work out where they came from, where their origins were. What sort of things are going on in this kind of area of recreational genetics that intersect with the sort of work that you do?
Mark - Well, you're right to say that people want to know where they came from or where their ancestors came from and there's a big problem there because each one of us has two parents and they have two parents each, and so on back in time. So, if you go back just a few hundred years, the number of notional ancestors anyone of us had is much greater than the current population of the entire planet. So, we have many ancestors in common which explains why that number thing happens. But at the same time, for any one of us to say, "Well, where did my ancestors live, say, 1,000 years ago?" is a meaningless question because they must have lived in many, many different places. So, the simplest and most accurate answer to that question is everywhere.
So, there's a tension there between the public wanting this kind of ancestry story, the sort of, 'who do you think you are' story about their genealogies, and what genetics tells us about ancestry which is that it is complex, multifaceted and we have many ancestors. So again, that's why there's been this focus, going back to mitochondrial DNA and Y-chromosomes. That's why those have become such a focus because there, there really is a single ancestor at some point in time that you can point to and say, "This man is my great, great, great, times 'n' grandfather or this woman is my similar grandmother." And there's a great attraction to that.
What it leads to is a focus on those two kinds of ancestors - the patrilineal and matrilineal ancestors - simply because they're easy to understand and think about. But they're no more special than any other of the ancestors that we would've had at that time.
Kat - They're just the ones we can spot.
Mark - They're the ones we can spot, exactly. I think that there's burgeoning in the number of companies doing genetic ancestry testing and I think some of them, they try and oversimplify things, such that they're saying something about somebody's ancestors from a single lineage and that's a bit of a slightly misleading to do, I think.
Kat - So, given that you're very well-known for working in the area of genetics and population studies, do people often contact you with questions about their family history, about their genealogy? What are the most common things that people ask you about?
Mark - Yes, we do get a lot of queries. I mean, some of them are quite surprising and amusing. So, there's a strong desire among men in particular to be connected to the Vikings in the past. More broadly and seriously, we get quite a lot of questions from people who phone up or send emails about events in their own family history. Particularly common is people who found they've been born by artificial insemination by donor. So, they have no information about their father or people who turn out to be adopted. And again, there's no information.
Kat - And finally, have you had your genome analysed in any way and what did you find in it if you did?
Mark - Well, not very comprehensively. No, I act as a kind of control DNA sample in every experiment that's done in the lab. So, I know my Y-chromosome type which is called I1a and it's one of the ones that people regard as a Scandinavian lineage so that much I can tell you. The rest of my genome, I can't really tell you anything about. I've showed a surprising lack of interest in my own genome, given that what we do is work on everybody else's.
Kat - That was Professor Mark Jobling from the University of Leicester.