Mad about Science: DNA Ancestry

Zach Hagadone
Reader Staff

When my aunt and uncle visited a couple of years ago from England, the latter brought along a folder of genealogical research he’d compiled about his side of the family — to which I’m connected through my mother. According to what he found, our family could be traced back to an illustrious Scottish clan whose most prominent member served as the lord high admiral during the time of James IV in the 15th and 16th centuries. Further in the past, our ancestors were involved in the wars between the pope and Holy Roman emperor in the 12th-14th centuries. Not only that, our people were the leading family of the faction known as the Guelphs. Through that line, we could trace our lineage to a minor branch of the Medicis. Gazing yet deeper into the mists of time, we found a direct connection to Alfred the Great, king of the Anglo-Saxons. It just got more and more illustrious — and more dubious from there.

Of course I want to believe that I’m descended from grand admirals, ruling families and ancient kings, and I’m not alone. Ancestral research is among the most popular hobbies among Americans, and it’s become a billion-dollar, high-tech enterprise. 

While my uncle used old-fashioned written records for his research, a 2019 report from the Pew Research Center found that a full 15% of U.S. adults reported mailing a sample of their DNA to testing companies like AncestryDNA and 23andMe. That number is certainly higher five years later — especially accounting for the COVID-19 lockdown era, when people were already sitting at home spending hours online and engaged in general navel gazing. And what is genealogical research but gazing at the navels of your ancestors?

All that said, the science behind those DNA results that tell us we’re related to Genghis Khan is simultaneously more complicated and less instructive than it first appears.

DNA is a molecule in your cells composed of chains of alternating groups of sugar and phosphate. Those chains are connected via bases attached to each sugar. Those bases bond chemically in specific ways in various sequences. Encoded into those sequences is all the biological info necessary to make an organism develop and function. 

All that DNA information is (usually) organized into 23 pairs of chromosomes that about half the time don’t pair up, giving us combinations of XY (men) and XX (women). Meanwhile, RNA — sometimes called DNA’s “cousin” — grabs that biological info from DNA and runs around doing the business of building cells and, in the process, regulating how the genes around which the DNA is arranged are read and expressed by those cells. 

The DNA in your body might contain the instructions to give you your grandmother’s nose, but you won’t grow it unless some form of RNA tells your cells to make it so.

However, genes are the least of what’s contained in our DNA. About 97% of what’s encoded in your DNA is what geneticist Adam Rutherford, writing in Scientific American in 2018, described as “a smorgasbord of control regions, scaffolding and huge chunks of repeated sections. Some of it is just garbage, left over from billions of years of evolution.” 

What’s more, the National Human Genome Research Institute states that “DNA from any two people is 99.9% identical. … The differing 0.1% contains variations that influence our uniqueness, which when combined with our environment and social contexts give us our abilities, our health, our behavior.”

That 0.1% is what we’re really looking at when we run a swab around our cheek or spit into a tube and mail it off in search of ancestral revelation. 

Here’s how it works (basically), according to the National Institute of Standards and Technology: DNA is extracted from the spit you sent to the lab and measured against the human genome. Technicians scan millions of areas in the genome simultaneously, flagging tiny differences. 

Once identified, those variants are measured by breaking the DNA in your sample into single strands, then sliced even finer and reexamined to see which of your variants bind to the same variant in the wider genome. 

The lab then looks to see which of those bonded variants match the ones uniquely associated with DNA found in people from various geographic areas. The degree to which those variants link up indicates whence in the world your ancestors may have come, and that’s what the DNA test company will tell you on a percentage basis.

But our DNA isn’t a pie chart. Rather than being “30% Irish,” the test indicates there’s a 30% confidence rate that variants in your DNA indicate someone in your family tree came from Ireland. As Stanford University Professor Marcus Feldman said in a Popular Science article in 2019, “You can’t take your DNA and chop it up and say, ‘This bit came from here, and that bit came from there.’”

While you inherit all your genes from your parents, because DNA gets shuffled around with every generation, it’s likely that you and your sibling got different portions of whatever DNA your parents got from their parents and so on (unless you’re identical twins). Because of that, some of your DNA might go back eight or nine generations while you may share very little if any with a grandparent from five or six generations ago.

So what does DNA ancestry really offer? Not much more than an estimate, and certainly no centuries-spanning indicator of personality or identity — those things we get from the people living around us today and the social, cultural, political and environmental structures and systems into which we’re born.

It makes me a little sad that I probably share nothing with my lord high admiral grandpa, but it does remind me to think more about the folks around me than the ones who died long ago.

Stay curious 7B, and look forward to Brenden Bobby back in this space next week.