Um...98% of DNA is most certainly not inactive.
http://en.wikipedia.org/wiki/Noncoding_DNA
Depends on what you mean by "inactive", but noncoding DNA still performs valuable functions, even if its not coding.
Much of this DNA has no known biological function and is sometimes referred to as "junk DNA"
"Increasing evidence is now indicating that this DNA is not "junk" at all. Especially, it has been found to have various regulatory roles. This means that this so-called "non-coding DNA" influences the behavior of the genes, the "coding DNA", in important ways. "
http://www.psrast.org/junkdna.htm"The idea that a major part of our DNA is "garbage" ignored the fact that a key feature of biological organisms is optimal energy expenditure. To carry enormous amounts of unnecessary molecules is contrary to this fundamental energy saving feature of biological organisms. Increasing evidence are now indicating many important functions of this DNA, including various regulatory roles. "
"We have a greater percentage of junk DNA in our genomes -
50 percent - than the mustard weed (11 percent), the worm (7 percent) or the fly (3 percent). Also, shockingly, there seems to have been a dramatic decrease in the activity of repeats in the human genome over the past 50 million years - as if the human species decided 50 million years ago to stop collecting junk. In contrast, there seems to be no such decline in repeats in rodents. (See Vignette 6)"
http://www.genome.gov/10002192