Friday, October 8, 2010

Y Chromosome tinkering

There are two genetic things in our biology that are very gender specific. Your mitochondria came strictly from your biological mother. Mitochondria are little structures in your cells that function as their power plants of sorts, and have completely different DNA than the rest of you. (It's speculated that they were a completely different organism that incorporated into our ancestors symbioticly.) If you're a man, your Y chromosome had to come from your father. I bring this up on the heels of many news stories about the mitochondrial Eve and the Y chromosome Adam. No, these are not backings for creationism, and there's a logical reason for this.
As you may be aware, people have 2 biological parents, which means that for ever n generations, they had 2n ancestors. However, not all of these were unique, as merely 250 is greater than the entire population of the earth. Some people had more than one child, (often way more in the past, when it wasn't clear that many of them could survive) and only some people went on to have their own children. (Some where infertile, killed, or just never got a mate in the first place.) Also, with a limited pool, family trees aren't perfectly branching. Some people married (usually distant) cousins, and basically, everyone on earth is at least 50th cousins with each other. Also, there were numerous bottlenecks in human genetic history. Disasters wiped entire civilizations off the map. At the most imperiled time of our species history, there were only 10,000 living humans on the planet.
So, while the mitochondrial Eve, a woman who lived some 200,000 years ago, is the ancestor of basically every human alive today, she was not the only living woman of her time. The other women's mitochondrial lines died out when either they had only sons (who would not pass on the mitochondrial DNA) or no children at all, leaving only hers. Same for the Y chromosome Adam, an ancestor of all men alive today who lived 60,000 years ago. He was not the only man alive, but the other men's lines all ended across the 60,000 years when they either had only daughters (who do not have a Y chromosome) or no children at all. This was further sped up by Genghis Khan, a Mongolian ruler who had a lot of children, who in turn had many more children. He is the ancestor of 16 million people today. Being a powerful Emperor probably did have a part of the ladies interest in him, as did his reputation for being wealthy and benevolent.
However, some signs show that our genetic bottlenecks may be disastrous for us. The Y chromosome has been shrinking over time, which may slowly damage male fertility (should those genes, located in the Y chromosome, be lost), or perhaps even end altogether, leading to an all-female humankind. (We could technically survive, but it would be...inconvenient.) The shrinkage is mostly due to interference from the Y chromosome's rival, the X chromosome, which you need to live. The most critical of the Y chromosome's genes are a group called SRY, which is responsible for 99% of what people think of when they think of men. In some species, the Y chromosome has been destroyed, but their SRY migrated out, so they still have males.
So to improve the genetic state of humankind, I would like to see some volunteers, dissatisfied with the genes they inherited, undergo a retrovirus-based retooling of their genome. This would hopefully prove helpful to them, in some way or other, and their new genomes would make them genetically unrelated to anyone on earth, and thus the best person to marry if you want to avoid inbreeding.
There is one particular group of pacific islanders, I can't remember their name right now, who would be the most interested, as their tribes have a tradition of marrying passing sailors as a way of avoiding incest on their tiny, historically isolated, island. (Children of an outsider are less genetically related members of the tribe, and thus more eligible for marriage, see?)

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