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It’s not always that genetic DNA testing gives you all the answers you were seeking. More often than not it leaves you with even more questions than before and results that sometimes seem impossible.
It doesn’t matter which DNA testing service you use. It’s hard to say that this or that is the most accurate DNA test. They all operate within the limits of an imperfect science that is based on estimates.
Your genetic testing results are highly researched estimates based on rigorous testing and decades of research. But they are estimates nonetheless.
So, no, genetic DNA testing is not always accurate. In fact, it is never 100% accurate.
But in most cases it’s close enough that you can make accurate inferences about your ancestors and relationships to DNA matches.
For instance, by looking at the number of shared segments between you and a match, you can infer that they are a first or second cousin. If you share 3400cMs (centiMorgans) with a match, then they are likely to be your birth parent or child.
Combined with other research methods, DNA testing often proves to be a powerful tool.
Genetic DNA testing tends to be pretty good when it comes to predicting the relationship between close family members like siblings, parents and children and close cousins.
But things become fuzzier the further away you go. That’s why most DNA testing services go up to the 3rd cousin level. Beyond that, any relationship predictions are mostly speculative.
But even for close relationship, it’s easy for a DNA test to mistake a sibling for a parent, an uncle for a grandchild or an identical twin sibling for a child.
It’s not just in family matching where imperfections show up. The ancestry report may not be completely on target as well.
Your ancestry breakdown may contain ethnicities that you are almost sure are not in your family line.
To be fair, it could very well be that you don’t know everything about your family’s history. But it’s also very possible that it’s the DNA test report that’s inaccurate.
So why is DNA testing full of estimations and possible inaccuracies?
Don’t all those scientists in the labs know what they are doing or are they just grabbing our money and taking us for the ride?
Scientists are trying their best to give you the most accurate information. In most cases, they do a laudable job.
Blame the science instead.
The human DNA is incredibly vast and complicated.
Early this millennium, an international group of scientists finished a 15-year project mapping the human DNA and sequencing all 3 billion nucleotide base pairs.
But even more than 15 years after the Human Genome Project was completed, we are still in the infancy of studying all that it uncovered.
When you submit your DNA to companies like 23andMe and AncestryDNA, they only test a portion of it. No individual company has the resources to map out your entire DNA.
Basically, there is a lot we still don’t know about the human DNA and there is lots of research that is still ongoing.
So the imperfections we see in health and genetic DNA tests are inevitable.
But the good thing is that we are slowly learning more about DNA and test reports are bound to get more accurate with time.
There is no big red sign in your DNA that says so and so is my sister and someone else is my first cousin.
What geneticists do is take your genes, put them into a computer in a digital form and compare them to all the other genes they have in their database.
The amount of genes you have in common gives them a rough idea of what kind of relationship you have with found matches.
If let’s say you share 1,500cMs with a match. He or she might be an uncle, aunt, grandparent or half-sibling. If the cM count is 3,400, it could be a child, parent or identical twin.
So there’s no definitive answer, just a range of possibilities.
The inherent deficiencies in comparative science are also apparent in ancestry breakdowns.
An ancestry composition report might suggest that your grandfather is 30% German but you are almost sure he was part French without any Italian blood in him.
The problem is that the test is comparing your grandfather’s DNA with DNA taken from the current population which could be very different from when he lived in Europe decades ago.
The accuracy of ancestry tests changes from one population to another.
For instance, it might be very accurate in nailing down that you have Scottish ancestry but become vague when it comes to breaking down African ancestry.
This is because their database might have more Scottish DNA tests to compare your DNA to but fewer African DNA tests.
The good news is that a lot of DNA testing services are getting better at this. They are making efforts to expand their databases through self-funded research, collaborations with other researchers and open source DNA data.
They are continually issuing updates that provide more refined ancestry breakdowns. So even if you took your test a year ago, the report will keep getting more accurate.
That’s why it is important to revisit your account now and then to check for new updates.
One big misconception people have when they first get a DNA test is that it will reveal all the answers they are looking for. That couldn’t be further from the truth.
A genetic DNA test is simply a tool among many you can use to trace your ancestry and find family members.
It is inadequate on its own. But when combined with other tools like family trees, genealogical records and family stories, it can fill in a lot of missing pieces.
I'm just another amateur genealogist investigating my American-Scots-Irish lineage. I built MyFamilyDNATest.com after buying all of the leading DNA tests to discover everything I could about my family history. Hopefully, this site will save you time and demystify the emerging science of DNA-based genealogy, for your family project.