Season 3, Episode 5: The God of Commerce
It turns out that “Patient Zero,” Mark Smith, was harbouring the Sinatra virus in his kidney – but the kidney had not always been his! He had had a kidney transplant. To help track the transplanted kidney back to its donor, the NorBAC team begins by checking the mitochondrial DNA in the kidney for sequences that might tell them about the donor’s genealogical background…
DNA footprinting?
Our tag line at the Ontario Genomics Institute is “The Future Is in Our Genes.” As we see in this episode, the past is in our genes as well. You may have heard of “DNA fingerprinting,” but did you know that scientists can also use DNA to trace the “footprints” of human populations over tens of thousands of years all the way back to a person’s ancestors in the distant past?
As explained in this episode’s Facts Behind the Fiction, mitochondrial DNA can reveal information about the maternal ancestry of a person or a group of people. You might wonder “what about paternal ancestry?” or tracing roots through the male lineage? For that, scientists look to the Y chromosome.
Like mitochondrial DNA, the DNA that makes up the Y chromosome – the male sex chromosome – doesn’t change much from generation to generation. Some changes, or mutations, will spontaneously appear from time to time as in mitochondrial DNA.
Changes that stick around through several generations give rise to “haplogroups” or groups of people that have a particular combination of changes. These can be traced back to the point at which particular mutations first appeared – the common ancestor for everyone within that haplogroup. Some haplogroups are common, while others are relatively rare, limited to select populations.
And if you trace back all the haplogroups, you eventually come to a common ancestor for all men on Earth. Nicknamed “Adam” in homage to the biblical first man, this common ancestor is believed to have lived tens of thousands of years ago.
Why go to all this trouble? Scientifically, it provides fundamental knowledge of great significance to anthropology, the study of human origins and social and cultural development. But, as this series continues to remind us, genetics has implications beyond scientific understanding.
The popularity of online genealogical websites – a Google search for “DNA ancestry” will give you almost one million hits! – is just one indication that many people find it interesting and fun to trace their family trees and learn from whence they came. For others, knowing that they are descendents of a particular person or group of people may have profound meaning and influence on their sense of personal identity.
For example, the Lemba people of southern Africa observe a number of Jewish rites and traditions, based on their belief that they have Jewish ancestry. But because their history and traditions are passed on orally from generation to generation, there was little “proof” of such origins. Several years ago, however, support for their oral history was found in their DNA, when a team of geneticists showed that many Lemba men belong to a particular Y chromosome haplogroup, which suggests an ancestral link to ancient Jewish populations.
What if geneticists had instead found evidence that challenged the oral history of the Lemba people? What might that mean for the Lemba? Would it require that they modify their traditions, their stories or their ways of life? Would it change anything at all?
Genomics & ethnicity
During his HBO special in 2000, comedian Dave Chappelle told a story about having once gone into a restaurant in which the server took one look at him and immediately assumed that, because Chappelle is African-American, he was going to order chicken. In recounting this incident of overt discrimination, Chappelle joked, “All these years, I thought I liked chicken ‘cause it was delicious. Turns out I’m genetically predisposed to liking chicken! ... I got no say in the matter.”
What does it mean to be “genetically” a part of one ethnic group or another?
In this episode of ReGenesis, the NorBAC team showed that the mitochondrial DNA in Mark Smith’s kidney had markers commonly found in Asian populations. Does that mean the donor thought of him or herself as Asian? From the DNA markers alone, we have no way to know; as Facts Behind the Fiction points out, we can’t even infer that the donor looked Asian.
Genetic research has shown that there are alleles that are found more commonly in certain populations than in others; in other words, there are some genetic characteristics that are shared among individuals within particular groups more so than between them. Skin colour is an obvious example: About 90% of the variance we see in skin colour is between commonly described racial groups, while approximately 10% is within those groups. Another example is sickle cell trait, which is more common in African-
Americans than in other North American populations.
It’s important to remember, however, that a given “group” is not uniform, nor is it entirely distinct from other groups. Not everyone who identifies as belonging to a particular racial or ethnic group shares all the same genetic traits as others in that group. Nor do they necessarily lack traits more common to other groups.
Besides, who is to say that a person can only identify with one ethnic group?! For many, the concepts of race and ethnicity are based not only upon genes and appearances but also upon ideology, shared experience and lived social realities. In our multicultural society, a person may relate to many different groups, regardless of the presence or absence of particular genetic markers.
All of that said, we mustn’t forget that there are numerous regrettable examples in history when claims about genetics have been used inappropriately to justify and perpetuate racial and ethnic discrimination.
Ongoing genomics research, like the Human Genome Diversity Project, allows scientists to catalog and better understand the nature and extent of genetic variation across diverse human populations, including different racial or ethnic groups. The information generated may tell us a lot about where we come from, and may have implications for our present – our health – and our future. But as this research forges ahead, scientists and society alike must be cautious not to allow new discoveries to be misused, intentionally or unwittingly, in discriminatory ways.
More food for thought
Q: How far back can you trace your family tree? If you could trace it back much further by looking at your DNA, would you want to? Why or why not?
Q: If you learned that your DNA contained markers common to a racial or ethnic group other than the one(s) you identify with most, what would that information mean to you?
Want to read and learn more?
To learn more about using mitochondrial and Y chromosome DNA sequences to trace human origins and migration, visit the website for National Geographic’s Genographic Project:
https://www3.nationalgeographic.com/genographic/atlas.html
To read more about genetic studies involving the Lemba, try these sites:
http://www.pbs.org/wgbh/nova/israel/familylemba.html
http://en.wikipedia.org/wiki/Lemba#Lemba_genetics
To learn more about genomics and race, read the text and explore the many links at this site:
http://www.ornl.gov/sci/techresources/Human_Genome/elsi/minorities.shtml
