It took another month for the computers in Castle Doom to fully analyse the tissue sample. Painstakingly, the machines rendered the cells down, from organelle to molecule, until they had dissected atom from atom, and the unravelled secrets scrolled in front of Doom.
He continued to contemplate the results he extracted from the Skrull tissue sample. He had determined that all Skrulls possessed 'X-Genes'; the very same that granted mutant humans their extraordinary powers. This highly flexible genetic molecule enabled the aliens to change their form at will. It appeared that all Skrulls had the conscious control to shift their form, but this did not explain the new proliferation of Super-Skrulls. He was forced to conclude that there was a further technological intervention or genetic engineering needed to produce these creatures.
Nevertheless, this revelation had allowed him to devise a simple test to detect non-mutant humans disguised as Skrulls. Mankind had long utilized devices to detect the X-Gene, spurred on by their fear of the mutants. A test based on the commonplace mutant detectors provided a simple approach for ruling out conventional humans as infiltrators.
For those disguised at mutants, a more in depth analysis could reveal if a Skrull had recently changed forms, as they left a large portion of 'junk' (more accurately called surplus) X-Genes that could be detected. Unfortunately, that level of testing would require blood samples. Furthermore, if a Skrull had been in the form of a mutant for more than a few days, it would be undetectable as the cellular machinery cleared away excess material.
Given that the aliens had proven that they were willing to leave agents concealed as a specific individual for years, this led to unpleasant implications: Until a superior method of detection was discerned, mutants could not be safely excluded as Skrull agents.
Fortunately for Doom, all of his personnel had genetic records assessed as part of their routine medical assessments. He also knew there were no mutants among his staff. He had secretly scanned all his personnel in Castle Doom, and was unsurprised to find that two of his people were alien infilitators; a low level scientist and a lieutenant in his security forces. Less than he expected, but more than he liked.
Rather than liquidating them, and thereby alerting the aliens to his hostility, he shifted his organization; both were promoted to what appeared to be important projects. He also ensured were surrounded by needy underlings; junior people, or those without confidence or initiative. The spies were buried under paperwork and the requirements of managing their slightly incompetent staff.
Fortunately, Doom's tendency to limit and compartmentalize his underling's knowledge of his operations limited what intelligence the Skrulls could gather.
As he continued to examine the Skrull DNA, he noted a few odd characteristics about it: on the nucleotide bases, there appeared to be extra molecules perpendicular to the normal base binding sites. It appeared to be a further binding site along the top-down axis of the genetic material.
One of the benefits of entirely rendering the cell down to its constitute parts was that now Doom could utilize computer models to test his initial hypothesis. While it was not something that could be used to come to final conclusions, it allowed him to quickly test ideas for soundness.
He summoned his DNA simulation model on a nearby screen, and adjusted some of the conditions. Most pertinently he had the DNA put in a form were these top-down bindings were mismatched and he choose to reduce the numbers of supportive nuclear enzymes surrounding the strings of DNA.
As the model ran, Doom felt the thrill of possibility manifest in him.
Indeed, just as he suspected, almost as soon as the model began, the DNA rearranged itself. Without the extra-genetic enzymes, these axial binding sites pulled the DNA apart and the molecules automatically rearranged themselves into what could only be called the 'default' state.
This explained two things: Why upon death a Skrull returned to it's natural state; and secondly, the vast excess of nuclear enzymes in the Skrull cells.
He smiled as he felt himself step closer to the answer he sought.