Evolution & Genetics: Human-Chimp-Fly Comparisons

[VonWeber]

Something I read promoting intelligent design states that science is disproving the connection between chimps and people. Now I read a science article on the matter and it states that the base pairs compare and there is about 1 or 2 % difference, but of the actual genes they are as much as 80% or so different. But from the way it sounds only one amino acid in a large protien has to change for it to be considered an entirely different gene. So the design argument didn't impress me much, but I do remember hearing for a long time that chimps' and people's genes were 98% the same. The other thing I heard once was that the genes of a person and another mammal (I can't remember which one, I think it was a mouse) are 90% the same. I've also read that most of the genes present in a person are present in flies also. Then recently I read that people have less then twice as many genes as a fruit fly. I guess what I'm wonder then is how different are human genes from an organism on a very different evolutionary branch like a fly when compared to human and chimp? For instance, they did a gene by gene comprison on a chromosome of a chimp and a person. Is this even conceivable between a human and a fly or is the chromosome layout radically different?

 

[iansmith]

You are asking good questions but the answer might be hard to understand if your lack a good background in genetics.

Statistics can always be misleading when taken out of context and when people do not specify what they are referring to.

The 1% to 2% is often an average cited for base-pair gene sequences. The stats would change if you compare the chrmosome sequences rather than just the genes.

Furthermore, I doubt that any given gene between human differ by more than 80%. 80% diffence would mean that both gene have evolved from two diffence source or it may serve a different function in human compare to chimps. It could also means that the gene is not use in either species. It is more likely that gene can be similar by 80%.

Also, one amino acid may change the function of proteins but it usually not the case. If the amino acid change to another amino acid witht the same properties then it is not likely that function is change and it basicly the same protein. To become a new protein, the amino acid change has to occur in a functionnaly important region. In a protein some region that have very little function will differ a lot more that those with important function when comparing several species. Also, if the amino acid switch cause an important function change, this change can disadvantageous to the individual and the change will not be pass on.

As far as difference between genes of different species, it depends if you are looking at the gene sequence of the protein sequence. The further a species is sperated by evolution the less the genes (base-pair) sequence are similar. However, you could compare two proteins from two species that have great evolutionary distance and find a high similarity between both proteins sequence and very little similarity between both genes sequences.

When comparing genes/proteins, you also have to consider the function of the protein. If the protein is important, then the sequence is not likely to have great difference because mutation tends to be harmfull in this case. If you look at a gene that does not have the most important function, then you can expect large difference.

 

[Phobos]

Some info I've found from various references (limited) re: % similarity in genes of nuclear DNA between humans and...

other humans - 99.9% similar
chimp - 95-99%
African ape - 98%
Mice - 70-90%
fruit fly - 60%
nematode worm - over 33%
round worm - 20%

 

[Astronuc]

Some interesting comments about evolution and genetics here

Evolution takes science honours
http://news.bbc.co.uk/2/hi/science/nature/4552466.stm

'Life code' of chimps laid bare
http://news.bbc.co.uk/2/hi/science/nature/4197844.stm

Chimps genetically close to humans
http://news.bbc.co.uk/2/hi/science/nature/3042781.stm