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Science of: Traits by Parent

By Aaron Wolf, Ph.D., Science Communications at Ancestry

Your physical and behavioral traits are often influenced by your DNA—usually hundreds or thousands of different DNA markers acting in combination. You inherit half of your DNA from each of your parents, which means both of your parents have influenced your traits in some way.

But that doesn’t mean that each parent influenced your traits equally. For any specific trait, certain DNA markers can have more influence. You may have inherited more influential markers from only one parent.

That’s why AncestryDNA developed traits by parent, a new way for you to see how much genetic influence each parent had on your traits. We can do this without your parents taking a DNA test. It’s all powered by our PRS trait models and SideView technology.

 

Predicting traits with PRS trait models

Most traits are determined by hundreds or thousands of different DNA markers, each having a small effect on the trait (Figure 1A). A trait like height, for instance, is determined by tens of thousands of DNA markers. At each marker in your DNA, you inherit two versions of that marker—one from each parent. These versions (also called alleles) can be the same or different, and have similar or opposite effects on the trait (Figure 1B). By looking at all these markers and which versions you have, we can measure their combined impact and predict your trait (Figure 1C).

Figure 1. This illustration shows how AncestryDNA predicts your traits using many DNA markers. A) Two parallel purple DNA bars display sequences of DNA marker letters — A, C, T, and G, which represent the four nucleotide bases in your DNA (adenine, cytosine, thymine, and guanine). The top and bottom rows show the two versions of each marker that you inherit — one from each parent. B) The same DNA bars appear again, this time with red and green arrows above each letter. Green arrows mark versions of a DNA marker that increase the likelihood of the trait, while red arrows mark versions that decrease the likelihood. C) A balance scale visualizes how the combined effect of all marker versions influences your predicted trait level. Green arrows tip the scale toward “more likely,” and red arrows tip it toward “less likely.” On the right, a horizontal prediction bar shows where your likelihood score falls between “Unlikely” and “Likely.” 
Figure 1. AncestryDNA predicts your traits using many DNA markers. A) Most traits are determined by many different DNA markers (the orange letters) spread across your DNA (the purple bars). You inherit two versions of each marker—one from each parent (the top and bottom letters). B) Each DNA marker impacts your likelihood for a trait—for example, whether or not you take naps. Some versions of the markers increase your likelihood of napping, while others decrease it. C) To predict your trait, Ancestry weighs the impact of all your DNA markers together.

To predict your trait, AncestryDNA scientists use a statistical tool called a polygenic risk score (PRS). A PRS is a long equation—sometimes called a “model”—that adds up the impact of the different versions of the DNA markers you have for a trait. (You can read more about how we build PRS trait models here.)

Of course, our prediction is only based on your genetic information. Many traits are also strongly influenced by environmental factors. So a lot could be impacting your traits that we don’t know about.

You can help us build new traits by completing our DNA surveys.

 

Organizing your DNA with SideView

We can predict your traits using a PRS score, but how can we tell which parent influenced that trait more?

That process begins with our SideView technology, which splits your DNA into the halves inherited from each parent. Remember, you inherited half of your DNA from each of your parents. But when we first read your DNA, we can’t tell which parts of your DNA came from which parent.

To sort this out, SideView uses your DNA matches. Because a match is usually related to you through only one parent, your matches can help us “organize” the DNA you share with them. You can think of them like magnets that separate your DNA into the halves inherited from each parent.

Figure 2. SideView uses your DNA matches to separate your DNA (purple bar) into the halves inherited from each parent—labeled Parent 1 (blue) and Parent 2 (green).

 

 

Finding out which parent influenced your trait more

Once we have your DNA separated into the halves inherited from each parent, we can easily  measure which parent influenced your trait more.

Using our PRS model for a trait, we look at each half of your DNA separately. Once we add up the effects of all the DNA markers inherited from each parent, we can tell you which parent’s DNA influenced a certain trait more.

Figure 3. This illustration shows how AncestryDNA separates your DNA into the halves inherited from each parent and determines which parent had the greater influence. A) Two horizontal DNA bars are shown, separated into two halves. The top bar is green and represents DNA inherited from Parent 1, while the bottom bar is blue and represents DNA inherited from Parent 2. Along both bars, DNA marker letters (A, T, C, and G) appear at matching positions, showing which versions came from each parent. B) The same DNA bars are displayed again with red and green arrows above each marker. Green arrows indicate marker versions that increase the likelihood of the trait, while red arrows indicate versions that decrease the likelihood. This shows how each parent’s inherited markers affect the trait. C) A balance scale compares the overall contribution from Parent 1 and Parent 2. More green arrows appear on Parent 1’s side, tipping the scale in their favor. On the right, checkboxes indicate “Stronger influence from Parent 1” is selected, showing that Parent 1 has a greater impact on the predicted trait. 
Figure 3. AncestryDNA separates your DNA into the halves inherited from each parent and measures which parent influenced your trait more. A) SideView separates your DNA into the halves inherited from each parent—labeled Parent 1 (green) and Parent 2 (blue). B) Ancestry keeps track of the version of each DNA marker you inherited from each parent and whether that version increases or decreases your likelihood of a trait, for example, taking naps. C) Because your DNA says you’re unlikely to take naps and Parent 1 contributed the most markers that decrease your likelihood of taking naps, we indicate that Parent 1 had more influence on that trait.

 

Your results are based on your DNA

Your results can’t tell you what your parents’ traits might be. Your parents only pass down half of their DNA to you, and the half they pass down is random. This means they have a  lot of DNA that isn’t shared with you.

For example, even if one parent passed down many DNA markers that influence you to take naps, that same parent may carry many other markers in their DNA that influence them not to take naps. The only way to know what a parent’s DNA says about their traits is for that parent to take an AncestryDNA test.

 

Building traits for the future

Ancestry scientists are committed to developing new and exciting trait predictions. Because building the PRS prediction models requires combining information from member surveys and DNA results, the power of our predictions relies on the data we get from our members.

You can help us build new PRS traits by taking DNA surveys.

 

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