Quote: (08-14-2013 10:38 PM)Wadsworth Wrote:
Quote: (08-14-2013 10:33 PM)gringochileno Wrote:
Quote: (08-14-2013 10:28 PM)Wadsworth Wrote:
Quote: (08-14-2013 10:21 PM)La Familia Wrote:
Quote: (08-14-2013 10:05 PM)Wadsworth Wrote:
It's theoretically possible I suppose. Altered genotypes do cause altered phenotypes. But normally the most minute change in genotype produces massive changes in phenotype. Normal physiology and biology exists within a pretty narrow range, because I suppose one way of looking at it is just as one massive chemical reaction. If you change the conditions of the reaction, the most likely scenario would be a hugely deleterious effect.
Not always true; if that were the case, then all of our silent mutations would be visibly evident and therefore, not silent.
One answer to your question is that in order for one to obtain super human abilities, the mutations must be beneficial. On average, most mutations in our DNA are neutral or deleterious. Additionally, you have to consider the increased energy cost required to maintain those improved traits, and that is dependent on factors such as the availability of resources in your environment or the rate of ATP production.
It's fun to think in what ways we can evolve to become more biologically efficient humans. Too bad we will most likely be exterminated before we can evolve and inherit perceived super powers.
Silent mutations don't occur on highly evolutionarily conserved genes. They normally occur in DNA stretches between genes. Alot of that DNA is malleable, and often contains viral DNA. If a highly conserved gene were mutated, the fitness of that organism would almost certainly tank and the gene would be selected against. Most mutations to genes aren't silent, they change the phenotype significantly.
I thought a silent mutation was one that doesn't alter the amino acid sequence of the protein the gene codes for due to redundancy in the genetic code. If that's the case, then why would a silent mutation in a highly conserved gene be selected against? (I'm genuinely curious; I'm not a geneticist and I very well may be missing something).
Yeah, the amino acid sequence of a protein is coded into the genetic sequence on a chromosomal gene. The sequence of DNA between genes is massive, and mutations often happen in those areas. If, for example, a mutation occurred in the gene for the androgen receptor, then the androgen receptor protein would very likely have an inappropriate amino acid residue somewhere in the sequence. The protein wouldn't fold properly, and it's activity would plummet. The phenotype of the organism would likely be massively different if even it survived (I don't think androgen receptor knockouts are viable).
You can get a silent mutation in a gene that won't change the amino acid residue, because lets say ACC and ACG both code for the same amino acid. Generally speaking, though, most silent mutations don't occur in coding regions.
Okay I follow you here. I think we have a terminological difference--I always understood the term "silent mutation" as referring specifically to a nucleotide-level change in a functional gene that doesn't alter the amino acid sequence of the resulting protein. You seem to also be including mutations that occur in non-coding regions. Maybe I was mistaken about this definition.
I agree that a point mutation changing a single amino acid in an essential gene is often completely devastating. Sickle Cell Disease and Cystic Fibrosis are classic examples of this. Even here, though, the exact amino acid that's changed seems to matter crucially--there are specific residues in the B-globin and chloride channel proteins that appear to be particularly well-conserved and liable to cause disease if they're mutated, while other regions of the proteins seems to be much more forgiving of changes to the amino acid sequence. It likely has something to do with needing certain parts of the sequence to have a certain charge in order for the protein to fold properly.
As an aside, people without functioning androgen receptors are viable, in fact knocking out the androgen receptor results in a very interesting disease!