Discovery of the Week: Gene Family Trees

My ‘discovery of the week’ post is something interesting I’ve found out recently, repeated here for your enjoyment or edification.

Every gene you have consists of two alleles – one from each parent. The combination of alleles in your DNA is unique to you (or at least, to you and your identical twin). However, each individual allele is an exact copy of an allele found in one of your parents, except in rare cases where mutation or recombination has occurred. This means that each gene has its own history of who it has belonged to and where its been.

Here’s an example. I have blue eyes. That means I have two ‘blue eyes’ alleles – one from my mum, one from my dad. These alleles are related to each other. At some point, certainly no more than 6,000-10,000 years ago but almost certainly much later, my parents had a common ancestor with a ‘blue eyes’ allele that was eventually passed on to me from both sides.

Next time I take a close-up of my own eye, I'm putting on mascara
Next time I take a close-up of my own eye, I’m putting on mascara

However, my mum has brown eyes. She has one ‘brown eyes’ allele and one ‘blue eyes’ allele (that she passed on to me). Her ‘brown eyes’ allele is very, very distantly related to my ‘blue eyes’ alleles – the split is at least 6,000-10,000 years old, and could go way back into prehistory, depending on when her ‘brown eyes’ allele split from the ‘brown eyes’ allele that first mutated to become a ‘blue eyes’ allele. So while I inherited 50% of my alleles from her, the alleles I didn’t inherit from my mum might have split from her alleles hundreds of thousands of years ago.

So here’s where it gets a little crazy. Humans have a number of different blood types – A, B, AB and O. These blood types are coded for by the ‘A’, ‘B’ and ‘O’ alleles. If you have blood type A, that means you have at least one ‘A’ allele and no ‘B’ allele. If you have blood type B, you have at least one ‘B’ allele and no ‘A’ allele.

So what? Well, it turns out that the ABO system predates humanity – we share it with chimpanzees. That means that the ‘A’ alleles of a person with blood type A are closer to that of a chimpanzee with blood type A than they are to the ‘B’ alleles of a human with blood type B.


I think that’s pretty cool.

By the way, I found this out from The Ancestor’s Tale by Richard Dawkins.


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