# Interesting Re-evolution Article



## tachikoma (Apr 16, 2009)

Why did this frog species suddenly evolve extra teeth?


Just thought this would be appreciated here.


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## epiphytes etc. (Nov 22, 2010)

definately interesting. i wonder what environmental pressures would cause teeth to reappear in an animal whose basic diet probably hasn't changed all that much? i mean bugs are bugs, right?


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## Okapi (Oct 12, 2007)

There must have been an allele that stopped the section of DNA that coded for teeth to function. The teeth were not needed so the lack of teeth didnt matter allowing the mutant anti-teeth allele to spread through out the population until it replaced the normal allele. Then 200 million years later, another mutation occurred that either replaced or disrupted the anti-teeth allele. What amazes me is that in the 200 million years that they existed without the teeth, mutations and transcription errors didnt destroy the suppressed section of DNA that did code for the teeth.


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## ETwomey (Jul 22, 2004)

It's an interesting story. There is this idea of "Dollo's Law" which states that a complex character, once lost, is seldom regained. No one seems to have a clear idea of why this is (Dawkins argued it's just a probability thing- what are the odds of following the same evolutionary path twice?), and to me it doesn't really seem intuitive, yet there are few examples where Dollo's law is broken. This seems to be one.


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## Morgan Freeman (Feb 26, 2009)

Oh wow. This is fascinating.

I can't even thing what selection pressures led to the re-evolution of these teeth. Unless perhaps they're useful for gripping bugs that are particularly wriggly!


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## Okapi (Oct 12, 2007)

Morgan Freeman said:


> Oh wow. This is fascinating.
> 
> I can't even thing what selection pressures led to the re-evolution of these teeth. Unless perhaps they're useful for gripping bugs that are particularly wriggly!


Control genes could account for that, regardless of selective pressures. Mutations happen all the time, and if they happen in a gene that controls the function of a set of genes, entire structures and body plans can change.
I saw a documentary on control genes once that explained how a handful of genes tell the rest of the genetic code how to function. They did alot of work with fruit flies and found that single gene mutations could cause different areas of the body to form into completely different things, legs in the place of eyes, different body plans, changes in wing structure, etc. Later in the show they focused on chickens, and explained that sections of DNA that coded for teeth to grow inside the beaks were in their makeup, but a single gene stopped that section from expressing itself. A mutation in that control gene caused it to stop working and allowed embryos to grow teeth. They then went on to discuss how feathers and scales are genetically similar and could be turned into eachother by the right control gene. This is apparent in the legs of birds, which are covered in scales. A control gene tells the cells in that area to create scales instead of feathers like on the rest of their body. The show ended with them discussing how, in theory, they could manipulate a few genes to cause chickens to grow teeth, scales, and a longer tail to make a dinosaur. 

Here are a few things I found trying to google that documentary:
Q and A: Jack Horner Wants to Re-Create T. Rex From Chickens
Study of Chicken Teeth Sheds Light on Evolution : NPR
Mutant Chickens Grow Full Set of Teeth - Science News | Science & Technology | Technology News - FOXNews.com
Atavism: Embryology, Development and Evolution | Learn Science at Scitable

The only thing that really amazes me about the whole process, is that the areas of DNA that code for complex structures would have a greater chance of being broken during periods of disuse. Transcription errors, mutations, and duplications are weeded out by natural selection if they are in areas that are expressed, and thus affect the animal's chances of survival. Dormant sections of code that are not expressed but still carried from generation to generation would not have such vigorous weeding of defects because they are not being used, and thus errors would not affect an individuals chances of survival. You would expect there to be some percentage of errors to affect unused areas of code, that in the event of them being turned back on, would cause the structure not to function correctly.


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## curlykid (Jan 28, 2011)

This could just be a trait that was constantly passed down a line where one parent had the trait but still had a dominant trait present. So it was never used but still in the DNA, until finally two parents carrying the trait produced offspring and then those reproduced and so on. Then one day vise-versa (dominant trait became more present), then later the recessive trait became present again. could be the answer, rather than a "major" DNA change.


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## Okapi (Oct 12, 2007)

Most traits are way too complex to have simple Mendelian genetics applied to them. Most traits are actually polygenic, which is what allows so much variation within a species. Unfortunately most basic examples of genetic traits that people know are single allele mutations, such as amelanism (aka "albino"). Since most traits are actually large sections of code, dictated by a number of control genes, events like the story above cant be explained by a population of hets (Aa) eventually producing a recessive (aa). All animals carry entire sections of DNA that code for structures that they as a species dont or cant express. Some sections are called junk DNA and seem to code for nothing, because whatever they originally coded for has been lost for so long that a multitude of transcription errors, duplications, jumping genes, and mutations have worked their way in. Thats what is so amazing about this occurrence. That section of DNA that was essentially baggage for generations was uncorrupted when the structure it coded for came back into use. I would love to hear Ed's thoughts on this.


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## Rain_Frog (Apr 27, 2004)

> Control genes could account for that, regardless of selective pressures. Mutations happen all the time, and if they happen in a gene that controls the function of a set of genes, entire structures and body plans can change.
> I saw a documentary on control genes once that explained how a handful of genes tell the rest of the genetic code how to function. They did alot of work with fruit flies and found that single gene mutations could cause different areas of the body to form into completely different things, legs in the place of eyes, different body plans, changes in wing structure, etc. Later in the show they focused on chickens, and explained that sections of DNA that coded for teeth to grow inside the beaks were in their makeup, but a single gene stopped that section from expressing itself. A mutation in that control gene caused it to stop working and allowed embryos to grow teeth. They then went on to discuss how feathers and scales are genetically similar and could be turned into eachother by the right control gene. This is apparent in the legs of birds, which are covered in scales. A control gene tells the cells in that area to create scales instead of feathers like on the rest of their body. The show ended with them discussing how, in theory, they could manipulate a few genes to cause chickens to grow teeth, scales, and a longer tail to make a dinosaur.


Was the show, "Dinosaurs: Return to Life?"

The show theorized that dinosaurs could be "retroengineered" from birds by manipulating existing DNA with viruses.


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## punctata (Jan 31, 2011)

I love the fact that they carry eggs in pouches on their backs.


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## Okapi (Oct 12, 2007)

Rain_Frog said:


> Was the show, "Dinosaurs: Return to Life?"
> 
> The show theorized that dinosaurs could be "retroengineered" from birds by manipulating existing DNA with viruses.


National Geographic's "How to Build a Better Being" I think, im watching it again to make sure.
Edit: No, I must have seen it on a different show. Ill have to see if I can find the one you saw, but I dont think that was it.

Edit:
Control genes are called hox genes
http://en.wikipedia.org/wiki/Hox_gene


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