DNA Fundamentals : Common DNA Testing Misconceptions

DNA Fundamentals : Common DNA Testing Misconceptions


If you’ve been following the DNA Basics blog series, you already know a lot about DNA, from what it is on a molecular level to how it’s organized, expressed, and how we test it to find out where your ancestors came from and new relatives you didn’t know about. This month, we’d like to look at some frequent DNA testing misunderstandings.


1) DNA testing necessitates the use of spit or blood.


In practically every cell in your body, your DNA sequence is nearly identical. That’s great for DNA testing since it means we don’t have to rely on blood or spit cells. A simple cheek swab is all it takes to take the DNA test. Epithelial cells are gathered on the swab when you gently massage it down the inside of your cheek for 30–60 seconds, and our lab can extract your DNA from those cells.




2) Full siblings should have the same outcomes as their parents since children inherit DNA from their parents.


While you do inherit 50% of your ethnicity from each parent, you do not necessarily inherit 50% of each parent’s ethnicity. If your mother is 50% Irish and 50% Scandinavian, you will not necessarily be 25% Irish and 25% Scandinavian. You get a random ethnic mix when you’re born. You may be ten percent Irish and forty percent Scandinavian in this case. The ethnicities you acquired from your mother should make up roughly half of your overall ethnicity estimate, but there’s no way to determine how much of each of her ethnicities you have without doing a DNA test. This is why siblings have such disparate outcomes! Your mother may have passed down 10% Irish and 40% Scandinavian to one kid and 20% Irish and 30% Scandinavian to another.



3) Your genetic ethnicity estimate will correspond to your known ancestry.


Your Ethnicity Estimate may differ from the ethnicities of your ancestors for a variety of reasons. You may not have inherited a significant quantity of ethnicity if it was handed down to you via several generations. Unexpected ethnicities may have been passed down to you from relatives you never knew about. Even the most strong trees don’t have enough branches to accommodate everyone.


There are other inherent constraints to DNA testing, such as the fact that certain populations share DNA owing to close geographic proximity, or migration patterns that have resulted in the mixing of formerly isolated gene pools. This is why you could see English instead of Scandinavian.



4) Your Ethnicity Estimate will include all of your ancestors’ ethnicities.


While it is true that each generation acquires the ethnicities of the previous generation, the quantity of each ethnicity we inherit can fluctuate. If your great-grandfather was half-English, for example, he may or may not have passed on all or part of his English heritage to his offspring. If his son — your grandpa — inherited any English, he may or may not have passed it on to his progeny. You may or may not have inherited a measurable quantity of your great grandfather’s English DNA two generations later.

Remember that half of your ethnicities are inherited from your paternal line and half from your maternal line, therefore each grandparent inherited one-quarter of your ethnicities. The further back in time you go, the less DNA you can assign to each ancestor. As a result, it’s fairly unusual to know for sure that a direct ancestor belonged to an ethnicity that doesn’t show up in your Ethnicity Estimate.