DNA testing through ancestry services like 23andMe and AncestryDNA has become increasingly popular in recent years. These tests analyze a person’s genetic makeup and can provide information on family history, ethnicity estimates, health risks, and some physical traits like eye color. But how accurate are they really at predicting something as unique as eye color? Here’s a look at what ancestry DNA can and can’t tell you about your eye color and genetics.
How DNA determines eye color
Human eye color is primarily determined by the amount of melanin pigment in the iris. Melanin comes in two forms: eumelanin which produces brown/black pigment, and pheomelanin which produces reddish/yellow pigment. The combination and ratio of these two melanins determines your eye color.
Several different genes influence the production, distribution and type of melanin in the body. The main genes involved in eye color determination are:
HERC2
The human eye color (HERC2) gene regulates expression of the OCA2 gene and is located on chromosome 15. It has a major influence over the ratio of brown-to-blue eye color. The HERC2 gene contains a key SNP (single nucleotide polymorphism) site known as rs12913832. The different rs12913832 alleles are:
| Allele | Eye Color Effect |
| GG | Higher melanin, brown eyes |
| GA | Intermediate melanin, green/hazel eyes |
| AA | Lower melanin, blue eyes |
So people with the GG allele will likely have brown eyes, people with GA may have intermediate eye colors, and people with AA will likely have blue eyes. Over 70% of people with blue eyes have the AA genotype.
OCA2
The oculocutaneous albinism II (OCA2) gene provides instructions to make the P protein which is involved in melanin production. Variants in this gene can reduce melanin levels, leading to reduced pigmentation and lighter eye colors. The main OCA2 alleles are:
| Allele | Eye Color Effect |
| CC/CT | More melanin, brown eyes |
| TT | Less melanin, green/blue eyes |
TYR
The tyrosinase (TYR) gene provides instructions for making the enzyme tyrosinase which is essential for melanin production. Mutations in TYR can cause oculocutaneous albinism type 1 which results in pale skin/hair and visual impairments. Variants in this gene can also lead to reduced melanin and lighter eye colors.
SLC24A4
The solute carrier family 24 member 4 (SLC24A4) gene helps provide instructions for making a protein that regulates calcium levels in melanocytes (melanin producing cells). Variants in this gene have been associated with lighter eye, hair, and skin pigmentation.
SLC45A2
The solute carrier family 45 member 2 (SLC45A2) gene provides instructions for making a membrane transport protein that helps regulate melanin synthesis. Certain mutations in this gene can lead to oculocutaneous albinism type 4 and reduced pigmentation.
How ancestry DNA testing analyzes eye color
Ancestry DNA tests like 23andMe and AncestryDNA look at hundreds of thousands of genetic markers across your genome. By analyzing certain gene variants associated with eye color, they can calculate probabilities for whether you likely have blue, green/hazel, or brown eyes.
Testing companies have developed eye color prediction models using machine learning algorithms and large datasets of genetic information. The algorithms compare your specific eye color gene variants against databases to predict probabilities for different eye colors.
For example, if you have the AA genotype in HERC2 and TT in OCA2, you would have an over 90% probability for blue eyes based on those variants. The more gene variants analyzed, the more accurate the eye color prediction.
Some key points about ancestry DNA eye color prediction:
– They analyze key SNPs in the HERC2, OCA2, SLC24A4, TYR and other pigmentation genes
– The more gene variants examined, the more predictive accuracy increases
– Results provide probabilities like: 80% chance of brown eyes
– Can’t definitively determine exact eye color, but provides likelihoods
How accurate are the predictions?
Studies evaluating eye color DNA tests have found they can predict blue and brown eyes with over 90% accuracy. However, predicting intermediate colors like green and hazel eyes is more challenging.
One study published in the journal Investigative Genetics found ancestry DNA testing could predict blue and brown eyes correctly over 95% of the time. However, for intermediate green/hazel colors the accuracy dropped to around 74%.
Another study in the journal Human Genetics compared DNA test results to self-reported eye colors for over 6,000 people. They found 95% predictive accuracy for blue eyes, and 90% accuracy for brown eyes. But just 46% and 67% accuracy for green and hazel eyes respectively.
So DNA testing is very accurate for predicting the likelihood of pure blue or brown eye colors based on genetic variants. But for more complex intermediate eye colors, the predictions are less reliable. Since eye color involves many genes plus environmental factors, testing has limitations.
Limitations of ancestry DNA for eye color
While ancestry DNA testing can predict eye colors with reasonable accuracy, there are some limitations:
– **Intermediate eye colors** – DNA testing is less accurate at predicting more complex green and hazel eye colors. The genetics behind intermediate eye colors are not fully understood.
– **Rare genetic variants** – There may be rarer genetic mutations affecting eye color that are not tested for or recognized by algorithms. This can lead to less accurate predictions.
– **Gene interactions** – Many genes and gene variants interact in complex ways to influence eye pigmentation. Testing may miss some of these nuanced interactions.
– **Environmental factors** – Other factors like sun exposure and diet can also impact melanin production and eye color, especially as people age. These are not accounted for in genetic testing.
– **Margins of error** – Results only provide probabilities like 80% chance of a certain eye color. Actual eye color may differ within the margin of error.
So while ancestry DNA testing can provide useful likelihoods for common eye colors like blue or brown, predictions are not 100% definitive due to genetic complexity and other factors involved.
Can DNA eye color analysis lead to new discoveries?
While eye color testing through ancestry DNA has some limitations, it is still useful for researching the genetics behind eye pigmentation. Through large databases and machine learning, scientists are discovering new gene variants and interactions that influence melanin production in the eyes.
Some potential benefits of ancestry DNA analysis for eye color genetics research:
– Find new SNPs associated with pigmentation and eye color
– Better understand the relationship between different genes influencing melanin
– Improve eye color prediction accuracy as more data is collected
– Discover rare genetic variants affecting eye color
– Study how eye color changes over a lifetime
– Understand interactions between genes and environment
So ancestry DNA testing gives researchers access to huge amounts of genetic data that can drive new discoveries about the biology of human eye color. Over time testing will become even more advanced thanks to this ongoing research.
Conclusion
While ancestry DNA testing can often accurately predict common eye colors like blue and brown, it has limitations when it comes to more complex intermediate eye colors. This is due to our incomplete knowledge of the many genetic and environmental factors influencing eye pigmentation. However, ongoing research using ancestry DNA databases will help improve eye color prediction and reveal new discoveries about the genetics behind this unique human trait.