If the organism is pressured, the non-coding DNA slowly fades. There are some parasitic organisms (eg Nasuia deltocephalinicola) that have highly compacted DNA:

If the organism is pressured, the non-coding DNA slowly fades. There are some parasitic organisms (eg Nasuia deltocephalinicola) that have highly compacted DNA: no introns, no regulatory regions, no transposable elements and even overlapping genes.