Recently, I read that a common field mouse has about a 97% match with human DNA. Is this accurate? 99% of mouse genes have human homologues (though their protein coding is only 70% similar); the detailed nucleotide alignment is only about 40%; which includes functionless DNA regions not under selection pressure.
Interesting discussion of the relationship between the mouse and human genome inWhat does the mouse genome draft tell us about evolution? by Alec MacAndrew
From the press release for The international Mouse Genome Sequencing Consortium
- Human Sequence: It's Bigger, but Is It Better? The mouse genome is 2.5 billion DNA letters long, about 14 percent shorter than the human genome, which is 2.9 billion letters long. But bigger doesn't always mean better, say scientists. The human genome is bigger because it is filled with more repeat sequences than the mouse genome. Repeat sequences are short stretches of DNA that have been hopping around the genome by copying and inserting themselves into new regions. They are not thought to have functional significance. The mouse genome, it seems, is more fastidious with its housecleaning than the human. Although it is actually accumulating repeat sequence at a greater rate than humans, it is losing them at an even greater rate.
- Shuffling the Chapters of an Ancestral Book. The mouse and human genomes descended from a common ancestor some 75 million years ago. Since then there has been considerable shuffling of the DNA order both within and between chromosomes. Nonetheless, when scientists compared the human and mouse genomes, they discovered that more than 90 percent of the mouse genome could be lined up with a region on the human genome. That is because the gene order in the two genomes is often preserved over large stretches, called conserved synteny. In fact, the mouse genome could be parsed into some 350 segments, or chapters for which there is a corresponding chapter in the human genome. For example, chromosome 3 of the mouse has chapters from human chromosomes 1, 3, 4, 8 and 13, and chromosome 16 of the mouse has chapters from human chromosome 3, 21, 22 and 16.
- Heavy Editing at the Level of Sentences. Although virtually all of the human and mouse sequence can be aligned at the level of large chapters, only 40 percent of the mouse and the human sequences can be lined up at the level of sentences and words. Even within this 40 percent, there has been considerable editing, as evolution relentlessly tinkers with the genome. The change is so great in most places that only with very sensitive tools can scientists discern the relationships.
- Preserving the Gems. Despite the heavy editing, about 5 percent of the genome contains groups of DNA letters that are conserved between human and mouse. Because these DNA sequences have been preserved by evolution over tens of millions of years, scientists infer that they are functionally important and under some evolutionary selection. Interestingly, the proportion of the genome comprised by these functionally important parts is considerably higher than what scientists had expected. In particular, it is about three times as much as can be explained by protein-coding genes alone. This implies that the genome must contain many additional features (such as untranslated regions, regulatory elements, non-protein coding genes, and chromosomal structural elements) that are under selection for biological function. Discovering their meaning will be a major goal for biomedical research in the coming years.