On average, you share about 12.5% of your DNA with your great-great-grandparents. This means that around 1/8 of your genetic makeup can be traced directly back to your great-great-grandparents. Here’s a quick breakdown of how much DNA you share with different relatives:
How DNA is passed down through generations
To understand how much DNA you inherit from different ancestors, it’s helpful to understand a few basics about how DNA is passed down:
- You receive 50% of your DNA from each parent.
- You receive 25% of your DNA from each grandparent.
- You receive 12.5% of your DNA from each great-grandparent.
- You receive 6.25% of your DNA from each great-great-grandparent.
In each generation, the amount of DNA you inherit is halved. This is because when sperm and egg cells are created, the DNA from each parent is shuffled and recombined. Only half gets passed down, essentially selected at random.
The 12.5% estimate is an average
It’s important to understand that the 12.5% estimate is an average. The actual amount of DNA you inherit from a great-great-grandparent can be anywhere between 0-25%. Here’s why:
- DNA is randomly inherited. You might inherit a little more or a little less than 12.5% from any one ancestor.
- Some ancestors contribute more DNA than others. If your parents were related, you would inherit a greater proportion of DNA from those shared ancestors.
- DNA can be lost over time. Small portions might be lost due to random chance as DNA is inherited from generation to generation.
While the exact number varies, on average, 12.5% is a good working estimate for how much DNA you share with a great-great-grandparent.
What that 12.5% of shared DNA means
Sharing 12.5% of your DNA with an ancestor may sound like a small percentage. But remember that human DNA is made up of over 3 billion base pairs. So 12.5% still represents tens of millions of genetic building blocks that you’ve inherited directly from that ancestor.
Those shared DNA segments do much more than just determine eye color or risk of certain diseases. They can potentially influence a wide range of traits, including things like height, facial features, personality, and talents. When looking at family resemblances, it’s remarkable how often the genes of a great-great-grandparent still make an appearance several generations later.
DNA comparisons with other relatives
Here is a table comparing the average amount of DNA you share with some other close and distant relatives:
| Relationship | DNA shared |
|---|---|
| Parent | 50% |
| Grandparent | 25% |
| Great-grandparent | 12.5% |
| Great-great-grandparent | 6.25% |
| First cousin | 12.5% |
| Second cousin | 3.125% |
| Third cousin | 0.781% |
Some interesting things to note from the table:
- You share just as much DNA with your first cousin as your great-great-grandparent. This makes sense, since you’re equally related to each.
- By the time you get to a third cousin, the amount of shared DNA is very small. Third cousins only share 0.781% on average.
- The percentages drop quickly with each degree of separation. But some DNA is still shared even with distant relatives.
Inherited traits from great-great-grandparents
Given that 12.5% of your DNA comes from each of your great-great-grandparents, what kinds of traits might you have inherited from them? Here are some possibilities:
Physical features
Genes influence your hair color, eye color, skin tone, height, build, facial features and more. It’s common to spot family resemblances even between distant relatives like great-great-grandchildren and great-great-grandparents. You might have your great-great-grandmother’s nose or your great-great-grandfather’s lanky build.
Physical abilities
Genes also impact your physical abilities. If your great-great-grandfather was a fast runner, you might have versions of genes suited for sprinting or endurance. Coordination and flexibility are also strongly influenced by genetic factors.
Personality
While personality is shaped by environment as well as genetics, DNA does play a role. Studies show that traits like extroversion, conscientiousness and empathy have genetic links. If your great-great-grandmother was outgoing and gregarious, you may share some of the same personality genes.
Interests and talents
Passions and talents have some genetic basis as well. If music, math, writing or art run in your family, you probably inherited an affinity for those activities. Great-great-grandparents can pass down genetic gifts or predispositions that still make an appearance generations later.
Disease risk
Unfortunately, inherited health conditions can also be passed down for multiple generations. Diseases like diabetes, heart disease, Alzheimer’s and many cancers have genetic risk factors. Reviewing the health history of your great-great-grandparents may provide insights about your own disease risks.
Ancestral origins
Your ancestors’ origins often leave subtle marks on your DNA. Genetic tests can identify percentages of ethnicity from different parts of the world. If your great-great-grandparents immigrated from a certain country or region, you likely still carry bits of genetic code reflecting those origins.
Learning more through DNA testing
DNA testing is the best way to learn more about your genetic connections with specific great-great-grandparents. Tests like 23andMe compare your DNA to other descendants to identify which segments you’ve likely inherited from each ancestor. The more DNA relatives who have tested, the more insights these tests can provide about your genealogy.
Autosomal DNA testing can also help confirm relationships and ancestors in your family tree when records are spotty. And when DNA doesn’t match expectations, it can reveal long-lost family secrets like adoptions, name changes, and false paternity events.
So while we share an average of 12.5% of our DNA with each great-great-grandparent, the amount can vary. DNA testing helps fill in the picture by showing exactly which segments of your genome originate with each of these ancestors.
Tracing your roots back through DNA
DNA testing can essentially let you trace branches of your family tree back through history. As you compare DNA segments with cousins, you can work backward to identify common ancestors. With enough DNA matches, you can eventually work back to identify genetic connections to specific great-great-grandparents or beyond.
This genetic genealogy approach is especially useful when paper records are hard to find. The DNA that you’ve inherited provides a link to ancestors even when the documentation is missing. With DNA testing, genealogists can work around gaps in the historical records.
Conclusion
Your great-great-grandparents contributed around 12.5% of your DNA, on average. This genetic connection influences many aspects of health, appearance, talents and personality that have been passed down through multiple generations. While the records may be hard to find, DNA testing can help uncover your genetic roots.