DNA, and old information

[Forestman]

Dose our DNA contain all the old information of the species that our species came from? For example, do we still contain the old DNA of the first mammals, or the reptiles that evolved into the first mammals?

[Danger]

All life on Earth shares something like 98% of DNA. In that regard, we retain almost everything from our ancestral species. There's also genetic memory (instinct) that is more species-specific. Wariness of snakes, for example, is inherent to species who are susceptible to venom. Most mammals share that, but mongooses hunt cobras. Each to his own.

[Coin]

However a lot of the shared DNA is in areas that are noncoding or otherwise inactive.

[Andy Resnick]

I think Danger is overstating the amount of common DNA, but it is certainly true that homologous proteins exist in mammals and yeast, for example. Even so, this is different than claiming humans have 'relic' DNA from when we were flagellates swimming in the ocean. DNA mutates over time. And we have DNA from (hypothesized) extracellular origin: mitochondrial DNA in animals and chloroplast plasmids in plants.

[Danger]

Sorry; I meant to say all animal life, and the number has got to be close to that. I haven't a clue as to how much we might share with plants and such.
Coin is correct as well. We have, for instance, the genes to grow gills... but they're clearly not expressed.

[Andy Resnick]

Can you provide a reference on that? Our current understanding is that less than 2% of our genome codes for proteins, and only 5% of our genome is estimated to be conserved over evolutionary timescales. We are homologous with chimps at the level of 95%, so I would expect similarities between humans and say, Drosophila, to be much lower.

http://www.sciencedaily.com/releases/2005/07/050727062750.htm

In addition, many fish are tetraploid rather than diploid. At the protein level, I have seen people present sequence homologies at the level of 50% and claim the proteins have identical function... at least in terms of model organisms.

I would also be interested to see a reference about 'gill genes' being present in humans. It would be interesting, because one would not only need gills, but the entire respiratory system would need to be adjusted- anatomically and physiologically. Your statement would imply there's an entire group of silenced genes.

[Danger]

Here you go.
Our results demonstrate that the parathyroid gland of tetrapods and the gills of fish most likely share a common evolutionary origin; both express Gcm-2 and require this gene for their formation, and both express PTH and CasR. We thus suggest that the parathyroid gland came into being as the result of the transformation of the gills into the parathyroid glands of tetrapods.

www.pnas.org/content/101/51/17716.full?ck=nck

[Andy Resnick]

Hey- that's cool!

I wouldn't say that means humans have genes to 'grow gills', tho... we have genes to grow parathyroids. :)

[Danger]

I might be mistaken about this, since I'm not a biologist, but it appears to me that the same genes are there, but are expressed differently.

[alxm]

In addition, many fish are tetraploid rather than diploid. At the protein level, I have seen people present sequence homologies at the level of 50% and claim the proteins have identical function... at least in terms of model organisms.

Try the wacky ba3 Cyt c Oxidase (http://www.nature.com/emboj/journal/v19/n8/abs/7593003a.html) from Thermus Thermophilus. Less than 20% homology and proven to have the same function! (It's less efficient though, but the gene is only expressed at low oxygen levels. Presumably it makes up for its lacking efficiency with higher oxygen affinity)

[Andy Resnick]

Here you go.


www.pnas.org/content/101/51/17716.full?ck=nck

I gotta thank you for showing me this- it's led to several fascinating discussions today. I didn't know about how the parathyroid regulates calcium.