Why do amino acid differences exceed nucleotide differences between humans and chimps?

[Monique]

By http://www.newscientist.com/news/news.jsp?id=ns99995044"

Humans and their closest relatives, chimpanzees, may be more different than geneticists have realized.

Previously, scientists have estimated that humans and chimps differ in about 1.5 per cent of the DNA letters that spell out their genomes. However, these estimates have been based on studies of only small subsets of the two genomes, because the chimp genome has not been sequenced precisely enough to allow a large-scale, base-by-base comparison.

That has now changed, thanks to the International Chimpanzee Chromosome 22 consortium, a team of researchers based in Asia and Europe that has sequenced a single chimpanzee chromosome in unprecedented detail.

The group then compared this sequence against its human counterpart, chromosome 21. They found that the two differ at only 1.44 per cent of the DNA bases that the two chromosomes have in common - a minuscule difference that confirms earlier estimates.

However, each gene contains hundreds or thousands of bases. This means even the tiny difference seen is enough to change the amino acid sequence of 83 per cent of the proteins generated by the 231 genes on the chromosome.

http://www.newscientist.com/news/news.jsp?id=ns99995044"

So even though that the sequences at nucleotide level only differ with 1.44%, the actual change at amino acid level is much larger.

 

[aychamo]

This is neat and all, but what does it mean? Don't chimps have the same types of lymphatic, immune, endocrine, and musculoskeletal systems that we have?

I know you aren't doubting common ancestor, but to me if a few extra percent differences between the genomes are found, it's not too big a thing. I frankly can't understand how someone could deny common ancestor when you see all the similarities between complex systems.

 

[Monique]

Well, just recently part of the sequence of the chimp was published, the rest is about to be released later this year. This is the first time that scientists have been able to compare large error-free sequences (an entire chromosome) between the two organisms (note I didn't use the species :P).

Since they know the exact sequence of every single base, they can predict amino-acid sequence from that. Every three bases codes for one amino-acid. I didn't see a number by what percent the amino-acid sequences actually differ, you'd have to look up the original Nature article.