Do you know where you came from?

Genetic test nowadays are dirt cheap. And your 23 chromosomes have amazing stories to tell, including details of your ancestry. In fact, white supremacist were quick to jump on the gene sequencing process to prove their "ethnic purity" only to find out that they weren’t all that pure after all. They were particularly disturbed to learn that all our distant ancestors were from Africa and we all were black! But I'm getting ahead of the story.

As you know, our 23 pairs of chromosomes are made of DNA, and everyone inherits half of their DNA from their mother and half from their father. 

When DNA is passed from parents to their children, the two chromosomes in each pair are randomly shuffled together. What you may not know is that when the chromosomes are shuffled, long segments from a single recent ancestor are broken into shorter segments. In the next generation the grandparent's segments are reshuffled and their fragments become shorter yet, and sometimes just disappear. Etc, the more generations back you go the shorter the segment and the fewer there are. 

A bit off topic, but sometimes mistakes occur and mutations are produced during the shuffling process. Most mutations are of no consequence, but sometimes they create problems, and sometimes they create solutions--meaning whatever occurs makes the organism more (or less) able to live in it’s environment, so it reproduces (or not) and the mutation is carried forward to new generations (or dies out). It’s an over simplification, but that’s essentially what evolution is all about—not so much “survival of the fittest” as it is “refinement of suitability” for a given environment(s). You get enough generations of changes and one species branches so far off you end up with something totally different, a new species. 

Anyway, different unique patterns of DNA, called markers, are found throughout your genome and, thanks to millions of tests, some of them are known to be from different people (perhaps I should write it People) in specific places around the world. There are oodles of markers in your genome and when you combine evidence from the hundreds of thousands of markers you carry, a clear picture of where you’re from and when develops. While the probability that you share DNA with a particular ancestor decreases as we go back over the generations, your total number of genetic ancestors does increase. By the time we get back to tens of thousands of years ago you are essentially related to everyone who left any descendants to the present day. So, since 50,000+ years ago everyone lived in Africa, the majority of your ancestral genome traces back to those African ancestors. 

Which raises the question, where did white folk come from? Using these same gene sequencing methods, we know that people who lived 7700 years ago, in what is today called Sweden, where probably the first to develop a light skin gene variant which survived in the gloomy north. Only about 5800 years ago light skin swept through the lower latitudes of Europe because by then people had acquired two light skin genes and the trait became much easier to inherit and thus more common.

Incidentally, 5800 years isn’t much on human timescale--hold your arms out to your side and modern man’s history spans from fingertip to fingertip. On that scale 5800 years ago is about where your wedding ring is, and you can remove all of modern technology from the steam engine to the iPhone with nail-clippers. A nail file would easily remove the entire history of gene sequencing.

Personally, I love that fact that we know all this in such detail that the genes have names and we know exactly where they are in our DNA. The oldest are called SLC24A5 (on the long arm of chromosome 15) and SLC45A2 (on the short arm of chromosome 5). You can actually see the long and short arms I’m referring to in the photos below. The arms on chromosome fifteen are hard to distinguish but obvious on five. There’s also a more recent third gene, HERC2/OCA2, that causes blue eyes and probably also contributes to light skin and blond hair. 

As an even further digression, you might be amused to know that if you unraveled all you DNA  it would stretch to the Sun and back 4 times.  DNA molecules are 1.7 to 8.5 cm long when uncoiled, or about 5 cm on average. You have about 10 trillion cells in your body (not counting red blood cells which don’t contain a nucleus or DNA), so if you stretched the DNA in all the cells out, end to end, they'd stretch over 744 million miles. The sun is 93 million miles away, so your DNA would reach there and back about 4 times!

Farther afield, we share about 90 percent of yeast's genes, of all things—there are exact counterparts in humans. Even stranger, there are 223 genes in humans that exactly match for those in bacteria. What’s more, researchers have found that bacteria have a way to do what’s called lateral gene transfer and it’s particularly prevalent in cancer cells. Either cancer cells are prone to these intrusions or the incoming bacterial genes help to kick-start the transformation from healthy cells into cancerous ones. In fact mitochondria, the powerplant in our cells, are decedents of ancient bacteria, and have their own genes that they swap them among themselves. Amazingly, there are scientists that think mitochondria have their own genetic interest that may not align with ours. Kinda creepy to think we’re just perambulating hosts. We're zombies!

Were not the only one to be invaded by bacteria. Look out the window; everything you see that’s green is thanks to a similar process.

About 2 billion years ago some cyanobacterium started functioning as a cellular component in plants. Thanks to them plants can use water, hydrogen and sunlight to create sugars that power the plant. In the process they create oxygen, lucky for us. All the oxygen in the atmosphere (about 20% off it) comes from that process (photosynthesis). We wouldn’t be here if bacterium hadn’t invaded plant cells just like mitochondria invaded ours.

How do we know? Genetics, of course! All the plants on earth, from giant redwoods to tiny single algae diatoms found everywhere, came from one single alga cell that swallowed a cyanobacterium with the help of a bacterial parasite. Every single plant shares the same DNA structure.

Turns out humans with blue eyes have a single common ancestor too. We all have melanin in our iris that creates the browns and greens, but a genetic mutation affecting the OCA2 gene turned off a switch that produces melanin in eyes, and the blue is what’s left.

Wow! Really?


Actuall Wow said…
It is actually wow!

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