Okay let us get this straight. The "junk" we are talking about is highly conserved. How did they determine this? Why, humans have that "same" junk! Now we can't experiment on humans to determine the function of this highly conserved "junk" so the mouse was used. Voila, not much harm(if any apparent) was caused to the mouse. Now why would the human have the "same" highly conserved "junk"? Remember there is no reason to fix the mutating DNA portions if it is "junk".
This is from an MSNBC story on it. Mice still thrive after loss of ‘junk DNA’
The scientists compared the genome of the mouse and humans and identified regions to delete. Using molecular engineering, they snipped out DNA sequences in mice embryonic stem cells and generated a strain of mice with the abridged genome.
I don't know about "highly conserved". If I read the abstract right, the sequences' similarities are at 70% to ours:
We deleted two large non-coding intervals, 1,511 kilobases and 845 kilobases in length, from the mouse genome. ... Together, the two deleted segments harbour 1,243 non-coding sequences conserved between humans and rodents (more than 100 base pairs, 70% identity).I can't find a decent reference to a percentage similarity number for the mouse genome as a whole vs. ours, but 70% doesn't seem like it should be any higher than the overall mouse vs. human figure. I did run across an interesting statement in this article:
"If segments of the genomes of two different organisms have been conserved (meaning the sequences are the same in both) over the millions of years since those organisms diverged, then the DNA sequences within those segments probably encode important biological functions."I suspect that the putative junk DNA regions they knocked out were in fact not highly conserved compared to coding regions.The search for functional DNA sequences that have been conserved between two different organisms across a large distance in evolution is the classical approach to comparative genomics that has been used to interpret the information in the human genome. In order for this technique to work, the conserved functional sequences have to stand out as distinct from the non-functional sequences that were not conserved. That degree of distinction requires the passage of time--lots of it--in order for mutations and the lack of selection pressures to cause the non-functional sequences in the two genomes to drift apart.
For example, mice and humans last shared a common ancestor about 75 million years ago, plenty of time for the non-functional sequences in their respective genomes to go their separate ways. Only about five-percent of the two genomes are conserved and it has been shown that most of the genes and regulatory sequences that have been discovered lie within these conserved DNA segments.