Of Potter’s Clay and DNA

 

¶   “A POTTER CREATES his or her most original work using virgin clay. A creator does so using virgin DNA. No! That’s true for the potter—It’s not true for the Creator.

‘Old’ DNA is as good as new

“Life-plans use genes over and over again, assigning them secondary tasks within a species even while they are performing primary functions vital to that species’ survival. After some 600 million years in the evolution of multi-celled animals, many genes seem overworked or ‘over-tasked’. However, before biology’s ‘Big Bang’ ushered in the Cambrian life-explosion, the same genetic material was under-worked by more recent standards. There are those who think that the genetic under-utilization of DNA’s abilities in ancient times explains the sheer explosion of variety at the dawn of the Cambrian. Multi-celled life, long suppressed while the cell itself evolved, took upon itself the genetic means to burst free, to express!

Design and control

“The University of Wisconsin’s Sean B. Carroll [1] led a team to hunt down genes that design and control the unfolding of basic body plans: a head, a torso, limbs. To general surprise, Professor Carroll’s team discovered that the same snips of genetic code wrote the blueprint for body plans right through the animal kingdom: from worms to insects, right up to animals with backbones, including fish, reptiles and mammals. In life’s grand scheme it matters not if a creature has four legs, or two wings; or that a body is clad in feathers, fur or scales. One snip from the genome fits all.

So much for gross similarities. What about fine differences, characteristics distinct to one species? Carroll’s team decided to find the gene responsible for painting large eyespots on a butterfly’s wings to repel predators.

“Each and every cell in a given embryo is equipped with an identical complement of genes. That is how a fertile worm or insect egg starts out—by multiplying identical, undifferentiated cells. But when undifferentiated cells in an embryo finish jostling to their final positions they undergo certain changes: whether a cell becomes part of a mouth, a gut-lining or a butterfly’s eyespot depends on which of its genes remain dormant, turned off, and which genes turn on.

A butterfly's eyespot scribed by DNA, by Alex Hyde, alexhyde.photoshelter.com

A butterfly’s eyespot limned by DNA. AlexHyde.photoshelter.com

“In the case of butterfly eyespots, Carroll’s team discovered that the genes turning on to build eyespots were already well known to science: they play a key role in building insect wings. It became clear that, as the branches on evolution’s tree reach out to become finer and finer twigs, specific genes in life’s DNA menu become ‘multi-tasked’.

“But how does a gene turn off, or turn on? If one thinks of a gene as one bead on a string, its central area determines which protein the gene will produce. But a line of ‘control switches’ strung beside the zone for turn-off or turn-on by its protein-coding switch takes its cues from the environment around it. This, in turn, varies at each stage of a creature’s development.

K D'Angelo http://www.obsessionwithbutterflies.com

K. D’Angelo www.obsessionwithbutterflies.com

“Each time a specific gene is instructed to ‘turn on’ it produces the same protein—it cannot do otherwise. But, each time it turns on it may be part of a different team of turned-on genes. Thus, one gene can play an integral role in creating a variety of characteristics, depending on which control switch turns it on, and when. So, the organ or biochemical produced by the collective gene-effort varies depending on specific environment-sensitive and time-sensitive permutations of turned-on/off genes.

Nature calls the final readout

A ‘holding place’ displays either DNA, digits or letters. As they move along the screen—through time, across space—they change. And their message changes with them.

A ‘holding place’ displays either digits or letters. As they move along the screen—through time, across space—they change. And their message changes with them.

“An analogy helps explain this mechanism. The LED readout panel on a telephone displays date, time, numbers dialed and so on. Any given letter or number is displayed on a ‘holding place’ having seven pixels vertically and five across. Depending which of those 35 pixels turns on, or off, and when they do so, the holding place shows either a C or a W, a 3 or a 7. Thus, the environment of a pixel —meaning, which of its neighbors are on, or off—determines the character it helps to produce—or not. Similarly, the sequence of a pixel’s ons and offs—here is the time element—determines whether the message scrolling along the panel may display the instruction to ‘create the brain of William Caxton’ or ‘the voice of Martin Luther King’. Thus, a small number of pixels generate a wealth of data, provided each element is correctly sequenced and timed. This, it seems, is also true of the electrochemical, sequenced instructions from which an egg grows up to be a beast.

Yes, but what is the designer?

“Such is the designer’s mechanism. But what designer sketches the designs and drives the bits to their destination and purpose in maturity?”   ¶

• • •

This excerpt: from “The Becoming” (U.K. 1988), and “Let There Be Life” (North America, 2002).

[1]  “Sean B. Carroll is an evolutionary developmental biologist … the Allan Wilson Professor of Molecular Biology and Genetics at the University of Wisconsin-Madison. He focuses on the evolution of cis-regulatory elements in regulating gene expression in biological development.”(Cis-regulatory elements are regions of non-coding DNA which regulate the transcription of neighbouring genes.)

Recommended: Nature: Butterfly disguise down to single gene, by Ewen Callaway

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