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A question on genetics and biology

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Botsareus:
I was watching NOVA the other night, and they were talking about that in large mammals the DNA does not really change too much from species to species. What do change is small portions of the DNA (on-off markers) which turn large portions of DNA on and off.

A few scientists think that live on earth was introduced by aliens. If this is true the most similar descendents of ancient bacteria should have on-off markers instead of actual changed DNA. Is that so? Or do this microorganisms have there actual DNA simplified?

Peter:

--- Quote from: Botsareus ---I was watching NOVA the other night, and they were talking about that in large mammals the DNA does not really change too much from species to species. What do change is small portions of the DNA (on-off markers) which turn large portions of DNA on and off.
--- End quote ---
Well, I think that is because mammals got a relative young ancestor. But to anyone with actual knowledge, do species take on-off activators with them from all species before them? How much is known, enough to play with dna and grab a random mammal dna, modify on-off markers, you got a other random mammal specie.


--- Quote ---A few scientists think that live on earth was introduced by aliens. If this is true the most similar descendents of ancient bacteria should have on-off markers instead of actual changed DNA. Is that so? Or do this microorganisms have there actual DNA simplified?
--- End quote ---
Eh, makes me think about the american "intelligent design".
Why should they have the on-off markers exactly? And well, what would it prove if they had?
And I dunno the answer on the question.

ikke:

--- Quote from: Botsareus ---I was watching NOVA the other night, and they were talking about that in large mammals the DNA does not really change too much from species to species. What do change is small portions of the DNA (on-off markers) which turn large portions of DNA on and off.
--- End quote ---
On off mutations do occur. A well documented example is a mexican family with a mutation that re-activated fur growth. If genes are off they can degrade, blind cave dwellers being a prime example. Their eyes are not just turned off, they are degenerated.
Having said that, not too much difference is relative. Humans and chimps differ less than a horse and a donkey. Horses and donkeys can interbreed, although offspring is infertile. Don't forget that a number of genes are virtually unmodified because they are to a large extent essential and derived through a common ancestor. The spinal chord is a good example. If you talk about large animals in terms of size, also remember that growing big means larger time between generations.

--- Quote from: Botsareus ---A few scientists think that live on earth was introduced by aliens.
--- End quote ---
panspermia is the word to google

--- Quote from: Botsareus ---If this is true the most similar descendents of ancient bacteria should have on-off markers instead of actual changed DNA. Is that so? Or do this microorganisms have there actual DNA simplified?
--- End quote ---

No, genetics is not as simple as gene on gene off. the plague does not carry genes that, if set to on, would result in a human.  

Numsgil:
Just to emphasize: DNA that is turned "off" tends to drift over time as mutations accumulate.

Botsareus:
ok, cool. thanks.

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