Posted on 02/09/2005 7:35:49 AM PST by PatrickHenry
By analyzing the genetic origin of a modest spot on a fruit fly wing, Howard Hughes Medical Institute researchers have discovered a molecular mechanism that explains, in part, how new patterns can evolve. The secret appears to be specific segments of DNA that orchestrate where proteins are used in the construction of an insect's body.
In the February 3, 2005, issue of the journal Nature, HHMI investigator Sean B. Carroll and his colleagues at the University of Wisconsin-Madison, published evidence showing that regions of DNA known as cis-regulatory elements have major evolutionary importance. Cis-regulatory elements are DNA segments that nestle around and even within gene segments that code for specific proteins. Rather than coding for a protein, however, these segments regulate the function of a nearby gene - and can allow for variations in that function depending on the tissue or developmental stage of an organism.
Different species of fruit flies exhibit remarkably different patterns of wing decoration. At the far right is the familiar Drosophila melanogaster, the workhorse model organism of genetics, which differs markedly from other fruit fly species.
Some biologists, including myself, have for many years suspected that cis-regulatory elements would be key to the evolution of form, said Carroll. The essence of our argument has been that proteins can have multiple jobs in the body at different times and in different tissues. Mutations in a gene's protein-coding region could exact an enormous penalty by affecting the function of that protein throughout the organism. But mutations in a regulatory region could affect only the production of the resulting protein in one setting allowing fine-scale variation with no collateral damage.
The amount of direct evidence for the role of cis-regulatory elements in evolution has been very small and very narrow in scope, he said. But in this study, we believe we present evidence that is of a smoking-gun variety.
The researchers chose to study the evolution of the wing spot on the fruit fly because it is a simple trait with a well-understood evolutionary history. While ancient fruit fly species lack the spots, Carroll said, some species that evolved later have developed them under the pressure of sexual selection. The wing spots offer a survival advantage to males, who depend on the decorations to impress females to choose them in the mating process.
In fruit flies, wing pigmentation depends on a gene known as yellow, which is found in fly species both with and without the spot. Since differences in the cis-regulatory elements controlling the yellow gene might account for variations in the spot, the researchers began by transferring potential cis-regulatory elements from the spotted species biarmipes into the spot-free species melanogaster. They attached the regulatory region to a gene for a fluorescent protein, and found that that gene was expressed in the spot-free species just as the yellow gene was in the spotted species, demonstrating the importance of the cis-regulatory region.
While the researchers later found evidence that changes in other genes were also involved in evolution of the wing spot, it was clear that evolution of the cis-regulatory regions of yellow was a critical step in the process. They therefore next sought to explore the origin and function of the cis-regulatory region itself. By comparing biarmipes, melanogaster, and other species, the scientists established that mutation of a preexisting regulatory region lead to the evolution of the spot pattern.
Importantly, they discovered that in the species with the wing spot, multiple mutations of the cis-regulatory region had created binding sites for existing regulatory proteins in the cell. By allowing these regulatory proteins to interact with the yellow gene, these new binding sites resulted in formation of a spot pattern. For example, the newly evolved binding sites included ones for a regulatory protein called Engrailed, which was already known to be used by all fruit flies to govern formation of wing structure. Binding of Engrailed to the regulatory region of the yellow gene is a necessary step in development of the wing spot.
Co-opting is central to the success of such an evolutionary mechanism, said Carroll. A key concept here is that this novelty arose from new combinations of old parts, he said. Through constant mutation, new binding sites for these existing regulatory proteins randomly evolve. And when the pressure of natural selection makes them create advantageous structures such as a useful wing spot they are preserved.
The evolutionary process of co-opting existing regulatory systems explains why the same structures such as spots on fly wings can evolve independently in distantly related species, said Carroll. The architecture of the wing is old and stable, he said. The vein pattern, the sensory organs, the attachment to the body all are ancient. So, for tens of millions of years, the same proteins have been available to modify patterns on the wings because they are there to do other jobs. When we see the same patterns evolving in distantly related species, we can theorize that it's just the same regulatory alteration of these existing systems happening again and again when selection favors it.
We like to use a Christmas tree analogy, said Carroll. These systems already have all the structural details in place, like the structure of a Christmas tree. And all evolution has to do is to alter these regulatory elements mutationally to bring out a pattern like hanging ornaments on the tree.
You're right. The question really was off-topic, and perhaps a rhetorical one. But there were some misconceptions I was just driven to respond to.... :-)
Well, I always assumed he stocked it for his family, and as for meat, well, if you're surrounded by water, fish would probably be the choice. You could then feed that to the carnivorous animals. Feeding the herbivores seems to be a problem to me. You would need a LOT of grains/greens/etc that they eat to keep them alive (how long was it again? 40 days & nights?). I think the text itself said something about God putting them at ease, so there'd be no "hunger accidents" (say, a lion eating a horse or a cow, which would be a problem for species repopulation...).
Excrement would be a huge worry, I think. Also, the close proximity of animals that can catch diseases from other species (I think some avian flus can infect swine, and people) raises doubts. Fresh water just came to mind, too. I guess he could catch rainwater on a clean linen sheet of sorts, and drain it into a clay vessel.
You are correct, and it drives them nuts.
God invented evolution.
Men invented organized religeon.
What's the difference? What mechanism prevents "micro" from shading into "macro?"
It's micro.
>>Actaully, inefficient evolution. Left in place all sorts of stuff not strictly needed. However, when things change, having that collection of garbage rattling aroudn int he DNA allows for useful changes.<<
So, the stuff has a purpose after all? Adaptability, say?
That is what micro-evolution is all about.
>>They just can't live with the fact that all life came from old pond mud somewhere. Too scary and they can't use their myths to make up rules for everyone anymore. Weak minds, moral prudes in denial.<<
"Old pond mud somewhere?" Who is dealing in myths here? 8^>
It would not be all that difficult to include the less than 8,000 "kinds" of air-breathing animals
Right. But there are millions of different creatures, not just a few thousand. Besides, ever see a dinosaur, last I checked, they were quite large.
Its like my zoology professor said, 'that flood fable was written before they knew about dinosaurs and how big they were and before they knew there was not enough water to cover mountains'.
> So, the stuff has a purpose after all?
Not necessarily. Sometimes it's simply due to replication error.
> a water canopy encircling the earth high in the atmosphere .... blocked harmful solar rays
Indeed. None of that pesky "light" getting through. Noah obviously built the ark in the dark.
> The ancestors of penguins, then, may have lived anywhere.
Alongside the lions and dodos, presumably. Because we've all seen those nature films showing just how vicious an angered penguin can be when trapped by hyenas or lions or tasmanian devils, we can rest assured that such critters would have had *no* trouble dealing with a different set of threats than what they have today.
> I'd be interested in seeing fossil evidence of where penguin ancestors lived....
http://www.cadicush.org.ar/olivero/amn.htm
And I'd be interested in seeing just how just about all the marsupials managed to get to Australia, without stops elesewhere. And how the flightless Kiwi bird managed to cross Asia and the Pacific to get to New Zealand. And how the flightless dodo got to it's little island.
Let me clarify: So, the stuff may have a purpose after all? After all, with the exception of the ID claim about the origin of life itself, none of this is abolute beyond what we witness in the wild and in the lab. 8^>
> So, the stuff may have a purpose after all?
To a certain limit of the definition of "purpose," sure. Just as a rock *may* have a purpose, if a need is found for it at some point.
And indeed, I'd be further interested in the non-plate-tectonics non-evolutionary explanation of why marsupial fossils are found in antarctica as well as australasia (but nowhere else). Hint to the creationists: ToE in combination with plate-tectonics predicted marsupial fossils would be found on Antarctica, and they were. "Creation Science" has a very poor (non-existent) record of that kind of startling succesful prediction.
Indeed, it's that very type of extremely counter-intuitive prediction that really lends credence to a theory. After all, before the theories of evolution and plate techtonics, who would have expected to find fossils of animals on an icy continent like Antarctica? Other examples of this abound. My personal favorite is a model of diffraction of light proposed by Fresnel. His model predicted that if coherent light were shined on a very small circular obstacle, that the diffraction pattern thus produced would result in a bright spot right in the middle of the shadow of the disk. Contemporaries laughed at his model. That is until the experiment was performed and the bright spot appeared right where it was predicted.
Ah, good point! Not only did they have to walk & swim all the way to the other continents (eating the bloated carcasses of the drowned animals along the way, IIRC), not one of them ate a bad meal or dropped dead from exhaustion. And needless to say, they all had to get to their far continents within one generation. So, for example, all the small Australian marsupials had to have reached Australia within a couple years.
Now, a creationist could counter that we're only talking two individuals from each kind, plus their children & maybe grandchildren, making the trek across the Earth, so we shouldn't expect to find the fossils of those who died along the way. Problem is, we're talking representatives of 8,000 kinds making the trek. So it would still be hundreds of thousands of individuals in all. You'd think there'd be some evidence of a mass radiation outwards from Mt. Ararat at a specific point in time.
I predict that if a creationist con-man (but I repeat myself!) writes yet another creationist book, it will be purchased by a large number of idiots.
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