Posts Tagged ‘Trisomy’

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Biology of Gilgamesh

July 25, 2012

Considered to be one of the oldest stories, the Epic of Gilgamesh originated in Mesopotamia most likely based on a 2500BC King of Uruk, which is now modern day Iraq. I could summarize the story, but in this Star Trek episode, Captain Picard does a mighty fine job.

Gilgamesh, though most likely based on a real king, is supposed to be 2/3 god and 1/3 human. Though we cannot precisely determine why the legend would include such an odd detail, or what the people who passed this story down were trying to say, I was curious as to how someone could be 2/3 of something and 1/3 of something, genetically. I have a few hypotheses that I would like to discuss.

Mathematically, this is impossible.

Because Gilgamesh most likely was human, we can safely assume he had two biological parents, like all of us. So the question is, how could the union of two people produce a person who is 2/3 one thing and 1/3 another thing?

Let’s say a god and a human have a child. That child (N) will be 1/2 god and 1/2 human, making him not enough god.

If N1 then had a child with a god, the new child (N2) would be 3/4 god and 1/4 human, making N2 too much god.

If N2 then had a child with a human, he would be way too much human, but if he had a child with a god, he’d be way too much god. So what if N2 had a child with a child like N1 (1/2 god 1/2 human)? He would end up with a child (N3) that is 5/8 god and 3/8 human, which makes him not enough god.

Diagram of the limit as it approaches 2/3.

If we continue this pattern, of child N procreating with child N-1, we will never get a perfect 2/3 god 1/3 human, and that is simply because we are working with pairs. No power of 2 will ever come out to be divisible by 3.

Perhaps there’s a third parent.

When a man and a woman love each other, they can make a baby. While his sperm donates 22 chromosomes and a Y, her egg donates 22 chromosomes, an X, and mitochondrial DNA. So genetically there is inherently some inequality in the amount of genetic information passed down. Disregarding the fact that the X chromosome holds so much more information than the Y, which really holds just the male determining genes (the SRY), the woman is responsible for giving her child good mitochondria, because her eggs hold the mitochondria that the developing baby must have in all of its cells.

Mitochondria are the energy producing organelles in the cell, and they originate from bacteria that formed a symbiotic relationship with ancient cells. Because they used to be bacteria, they also come with their own DNA. Even though over the years a lot of the mitochondrial genome has been transferred into our genome, quite a few important genes are still made in mitochondria, such as mitochondria specific proteins and mitochondrial tRNAs.

Mitochondrial DNA is also implicated in many human diseases as a result of the important genes it has. As a result, many have considered the possibility of a therapy for these diseases; instead of the mother giving her genome and her egg which holds the mitochondria, the egg and mitochondria could come from another woman who doesn’t have a mitochondrial disease. But this sort of procedure is still really in development and requires legal work to be done.

But even if the ancient Mesopatamians did have the in vitro fertilization technology to do this, one god’s mitochondrial DNA is certainly not enough to give her equal credit to the god and human that gave half their genomes.

Polyploidy

Though we are all diploid organisms, or organisms that have two copies of each chromosome with one coming from each parent, there are strange cases of having extra copies of chromosomes. The two most famous being trisomy of chromosome 21, which leads to Down Syndrome, and Kleinfelter’s Syndrome, which is where a man has 3 sex chromosomes: 2 X chromosomes and a Y. Unfortunately, these are the most well known because they are the only ones that are mild enough to lead to live births, any other kind of trisomy leads to death and miscarriage.

But these are just trisomies, where there is just one extra chromosome. Triploidy, or having three sets of each chromosome, definitely does not lead to a live birth, usually ending in miscarriage. These embryos come from either the egg or the sperm not properly dividing and thus still being diploid and not haploid. But the reason these embryos cannot develop is because there is just too much genetic information for the babies to handle. And in many cases, there are genes that we actually only want to have one active copy. Many of genes are called imprinted genes because only the mother or only the father’s gene is usually active.

So this is definitely not a reasonable explanation for Gilgamesh’s 2/3 god and 1/3 human genetics, but it does come the closest. If Gilgamesh’s godly parent donated twice as much DNA as the human parent, and he was still able to develop, then this could work. He would still have two parents, but his triploidy would make him genetically 2/3 god and 1/3 human. And who knows, maybe Gilgamesh’s godly genes have special proteins that can deal with the extra genetic information.

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