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I'm Just a Simple Man

dna2two


Ten years ago most genetic scientists thought that the human genome consisted of 100,000 or more genes.

When the working draft of the genome was published in 2001, scientists were very surprised to learn that the estimate of functioning genes fell between 30,000 and 35,000.

After further analysis, scientists in the U.S., Asia, and Europe announced this week that the estimate of functioning human genes is only 20,000 to 25,000.

The refined sequence reported in the science journal Nature is the most complete so far. It covers 99 percent of the gene-containing parts of the human genome, identifies 99.7 percent of known genes and is 99.9 percent accurate, according to the scientists.

Because it is so complete it will allow scientists to search for the causes of disease and inheritable factors that predispose people to illnesses such as diabetes or cancers.

Scientists also expect it to advance drug development by customizing treatments to genetic profiles.

The refined sequence identifies the birth of 1,183 genes in the last 60-100 million years and the death of about 30 genes in a similar period.

This is good news. If finding the cause of a genetic disease were like finding a needle in a haystack, the size of the haystack is only 25% of the size we thought it was a decade ago.

And if you were holding out hope for hidden utility in junk DNA, that doesn't seem to be the case. Junk DNA seems to be junk - at least in mice.mouse.jpeg

Mice born without large portions of their 'junk DNA' seem to survive normally. The result contradicts the beliefs of many scientists who have sought to uncover the function of these parts of the genome...

[Barbara Knowles from the Jackson Laboratory in Bar Harbor, Maine] cautions that the study doesn't prove that non-coding DNA has no function. "Those mice were alive, that's what we know about them," she says. "We don't know if they have abnormalities that we don't test for..."

"Survival in the laboratory for a generation or two is not the same as successful competition in the wild for millions of years," he [David Haussler of the University of California, Santa Cruz] argues. "Darwinian selection is a tougher test."

The remaining mystery: Why, if junk DNA really is useless, does nature carefully conserve much of this information over millennia?

Comments

Okay, so your mouse is cuter than mine. But did you see my alien fish? And my lion? And my robot?

Top that, smart guy!

Oh yeah...er, the DNA stuff is real interesting, too.

Phil:

I just saw a Kindergarten class program where they sang (out of tune), recited the Pledge of Allegiance (each at their own pace, but together), and did a Gingerbread Man skit.

You know what I learned?

Cute conquers all!

Bwaaahahahahahahaha!

If it turns out that junk DNA really is junk, then perhaps the answer is parasitism or failed parasitism. Either something gets replicated in that DNA section, or it consists of debris that hasn't vanished yet (perhaps including old virus DNA).

Karl:

You're right about parasitism. Some junk DNA is from viruses.

The mystery remains though. Why would parasitic code (or just nonfunctioning code) get faithfully copied for so long that even different species have the same junk?

Let's say that mutation is completely random and that we all have some small amount of mutation. If my mutation is solely in junk DNA I should be completely unaffected so that I could pass on the mutant copy of the junk to the next generation.

A mutant copy of functioning code would be less likely to get passed on. The conservation of that code makes sense.

What they expected to see was quickly changing junk. That's not what they found.

Oh well, we all love a good mystery.

Karl:

I wonder if its possible that our junk DNA isn't really old at all. I wonder if scientists just think this code is old because its often spread across so many species.

In other words, they think the code is old because they think it came from a common ancestor.

What if instead, much of this code is new and has been introduced across multiple species by viruses relatively recently?

Just a thought.

This would explain both why junk DNA is unneeded - you remove the fleas from a dog and he's still a dog - and widespread - cats have fleas too.

Stephen, you got me thinking along more interesting lines. If a considerable portion of our DNA serves no evolutionary purpose, has no obvious means to enforce propagation of itself, yet apparently survives tens of millions of years, then maybe we should be looking for hidden messages or something. After all, the genome is an obvious place for an alien visitor to store messages or other sorts of information.

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