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Author Topic:   Is DNA the TOTAL Instruction Set for a Lifeform?
Member (Idle past 1137 days)
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From: Prague, Czech Republic
Joined: 10-22-2008

Message 70 of 70 (628595)
08-11-2011 8:24 AM

Geometry and your intestines
I came across an interesting article on Pharyngula which seems relevant to this discussion. He'd describing research published in Nature* on the embryonic development of the gut.
Apparently, the folding patterns of the gut are pretty consistent within a species - they always fold into the same shape. Now, based around some of the naive views expressed in this thread, for this complex pattern to be caused by your DNA, there'd have to be some gene which makes this bit fold here, another gene which makes another bit fold there, and so on for a very long time - the intestines being so long.
These researchers very elegantly demonstrated that this isn't at all necessary. The gut develops embyronically as a simple tube, attached to a sheet of tissue called the mesentery. It's schematically illustrated in the diagram from the paper below.
These two bits - the gut tube and mesentery, grow at different rates, and as they do, the characteristic folds begin to set in. The researchers did a simple experiment using a rubber tube and piece of rubber sheet, shorter in length than the tube. They stretched out the sheet to the length fo the tube and then stitched them together. When they released the tension, lo and behold, the rubber tubing folded into a position remarkably similar to that of a chicken gut. In the figure below, the top pictur (b) is the rubber model, while the bottom picture (c) is an actual developing chicken gut.
This is a neat little demonstration that you don't need to encode the exact shape of a complex pattern to produce that pattern. All that needs to happen is for different cells to multiply at different rates, and simple facts of geometry will cause many of the complex structures present in animals and plants to take shape.
*Savin T, Kurpios NA, Shyer AE, Florescu P, Liang H, Mahadevan L, Tabin CJ (2011) On the growth and form of the gut. Nature 476:57-63.

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