Why some gene versions are dominant and some are recessive. Which in some ways is a good thing considering diseases like Huntington’s disease that are dominant. Or more blue eyes in Africa (see South Africa for example).ĭominant does not mean common. And there are other ways too of getting more brown eyes in Europe. Brown eyes would also become more common if a bunch of Africans moved in or many of the blue-eyed people were killed for some reason (witch burning?). If brown eyes gave an advantage, then it would start to become more common. The changes just don’t have anything to do with whether the trait is dominant or not. Now of course traits can become more common over time.
Whether an allele is dominant or not does not affect how common a trait is. Again the same eleven blue to one brown ratio. If they have 4 kids each, then we have 44 bb and 4 Bb. Since we aren't going to allow incest, the Bb folks will find a bb for a mate. Now these folks all pair up randomly and have 4 kids each. This is 2 people with brown eyes and 22 people with blue or green. Using regular old Mendelian genetics, we'll have 20 bb people from our 5 bb couples and 2 Bb and 2 bb from our mixed couple. The Bb person has 4 kids with one of the bb folks and each bb couple also has 4 kids. Imagine we start out with eleven bb people and one Bb person.
This is because brown (B) is dominant over blue and green (b). Remember, you will have brown eyes if you are BB or Bb and blue or green if you are bb. Without some sort of outside pressure, the ratio of blue to brown eyes stays the same. To simplify things we’ll call brown eyes B and not-brown eyes b. Let’s do a thought experiment to make this clearer. Your brown eyes can’t affect my kids’ eye color unless we get married. So why don’t their brown eyes dominate over time? Because in populations, dominant isn’t dominant over other people’s recessive gene versions.
Now this allele isn’t exclusive, there are still brown-eyed folks in northern Europe. Here the not-brown allele is more common even though it is recessive. In some parts of the continent, over 80% of the population has lighter colored eyes. Instead, it is because there are mostly brown alleles of OCA2 in the African population. This is an inherited trait in humans, where the dominant gene causes the cleft chin, while the recessive genotype presents without a cleft. This isn’t because brown eyes are dominant over blue and green. Nearly everyone in most of Africa has brown eyes.
The brown allele of OCA2 is dominant over the not-brown allele. We can think of OCA2 as having two versions, brown and not-brown. The decision on whether to have brown eyes or not is pretty much controlled by a single gene, OCA2. About … icon-addNote android4 Answer apple4 icon-appStoreEN icon-appStoreES icon-appStorePT icon-appStoreRU Imported Layers Copy 7 icon-arrow-spined icon-ask icon-attention icon-bubble-blue icon-bubble-red ButtonError ButtonLoader ButtonOk icon-cake icon-camera icon-card-add icon-card-calendar icon-card-remove icon-card-sort chrome-extension-ru chrome-extension-es-mx chrome-extension-pt-br chrome-extension-ru comment comment icon-cop-cut icon-cop-star Cross Dislike icon-editPen icon-entrance icon-errorBig facebook facebook-logo flag flag_vector icon-globe google-logo icon-googlePlayEN icon-googlePlayRU icon-greyLoader icon-cake Heart 4EB021E9-B441-4209-A542-9E882D3252DE Created with sketchtool.Let’s take eye color as an example.
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