quote:
Also, technically, introns and exons related to RNA, not DNA.
I don't know how they were originally defined (since I have no formal training in genetics), but intron and exon are routinely used to describe DNA in current genetics literature.
quote:
However, I would like to ask a question. You seem to be claiming that the "98%" similarity between chimp and human DNA includes ALL of the DNA, including so-called junk DNA. I am not sure that is correct. For example, the value "98%" was quoted way before the HGP had completed, and I don't believe the chimp genome has been determined yet. I think the "98%" value is based primarily on protein-coding regions, and on a large number of genes, not all of them. For an explanatory example of the general method I think the number is based on...suppose scientists determined the sequences of just 1,000 protein-coding genes in humans and also the seqeuences of the same 1,000 genes in chimps, then compared them, finding that large sample of protein-coding genes to be "98%" identical in sequence. If this is the case, the junk DNA would not be involved in the calculation.
Anyone know the actual method?
The original measurement was done by hybridizing DNA from the two species and seeing how easily they annealed. More recently it has been confirmed by sequencing, first of ~1 Mb segments of genomic sequence (i.e. including everything, junk and all) and now of both entire genomes. The measured value from comparing the full human and chimp genomes is about 98.7% identity. (The chimp genome has been fully sequenced, and a draft is publicly available, but the paper hasn't been written yet, so that measurement isn't published yet.) So yes, the quoted value includes junk DNA. Identity is significantly higher in coding regions, although I don't know by how much.
These numbers can be a little misleading, however, since they describe only single-base-pair differences in homologous sequence. If you include insertions and deletions, the fraction of divergent bases will be much higher (perhaps 5%, but it hasn't been well measured yet).