Even in the 21st century, we still have so much genetics left to discover!! There are lots of descriptions of these specific groups on the internet, even though it doesn’t look like there are any scientific papers describing them. In China, for example, the Hmong people 6 and the inhabitants of the village of Zhelaizhai 7 have reportedly high prevalence of blue eyes, likely due to an influx of European ancestors hundreds of years ago. This ancestor could be very very distant, possibly hundreds of generations ago. And since the traditional blue-eyed allele is recessive, each blue-eyed person would have European ancestry on both sides of their family. Scientists think the traditional blue-eyed allele near OCA2 had a single origin in Europe 6,000-10,000 years ago 5. 1) Some blue-eyed Asians do carry the classic European blue-eyed allele. So do Asians carry this blue-eyed allele? Let’s give three possible answers, based on your definition of the “blue-eyed allele”. So it’s safe to say: eye color genetics are complicated! So, Do They? And entirely new genes were found to influence color within South Asians, including LYST and TYRP1 4. In East Asians, other versions of OCA2 (different from the traditional allele) were found to have a strong effect on the darkness of the brown color. That means that even though these alleles have an effect in Asians, they aren’t the major contributors to eye color diversity in Asia. That is, an allele that produces bright blue eyes in Europeans might only create slightly lighter brown eyes in Asians 3,4.Īlso, the traditional European alleles are still at very low frequencies in Asians. ![]() One study of both Asians and Europeans showed that the same genes (including our friend OCA2) affect eye color in both groups… but the alleles have less dramatic effects in Asians. Less genetic research is done in people of other ancestries, and oftentimes the results don’t carry over perfectly. Our predictions only work well in Europeans. We now know that at least sixty genetic regions interact with one another to produce a particular eye color 3. So there must be something else contributing to the other 45%. Well, this one location only explains 55% of the variation in eye color. This is what is typically considered the “blue-eyed allele”, and it’s what places like 23andMe use to predict your eye color. To be fair, 55% of the variation in eye color (in people with European ancestry) is due to just one location in your DNA, which is near a gene called OCA2 2. With a population of 1.4 billion, this would mean 14 million Chinese people have blue eyes! The true number is probably a lot lower, so what's going on here? Turns out, there's a lot more to it than a single "blue-eyed allele." The Complex Inheritance of Eye Color ![]() Doing some quick math*, we can approximate that 1% of people in China should have blue eyes.īut 1% is actually pretty high. Let's take a closer look at China, which looks to have an allele frequency of approximately 10% on the map. But how does this translate into actual, blue-eyed people? So the map above shows blue-eyed allele frequency. So the percentage of actual blue-eyed people is lower than the allele frequency. Here, we'd say the allele frequency is 50% (5 out of 10 chromosomes), even though just 20% (1 out of 5 people) have blue eyes. Each person is shown with their two chromosomes and the resulting eye color. Let’s say we have a sample of five people, as shown below. Allele frequency is the percentage of chromosomes that have the chosen allele. This brings us to the first important thing to know about the map I showed you: it showed the frequency of the traditional blue-eyed allele across the world. That means you need two copies in order to end up with blue eyes: Under that model, the traditional blue-eyed allele is recessive. Why are blue eyes so rare?īiology teachers typically teach eye color as a very simple trait. ![]() So while many Asians do have the “blue-eyed allele”, blue eyes themselves are still quite rare. ![]() Adapted from Donnelly (2012) 1.īut this isn’t the same as the frequency of actual blue eyes, which are much rarer. The map below shows the frequency of the traditional blue-eyed allele across the world: This map shows the worldwide frequency of the traditional blue-eyed version of the OCA2 gene. Though as you get farther away from Europe, it becomes less common 1. Yes, some Asians do carry the "blue eyed allele".
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |