Mutants are a unique sub-variant of those extraordinary individuals known as metahumans. The public tends to lump many mutants and metahumans into one group. Mutants, specifically defined by the work of Nathaniel Essex have faced significantly more discrimination over the years.
The Celestial encoding in DNA that triggers a meta-crisis event in homo sapiens is usually buried deep in the amygdala. For mutants the encoding transfers to the chromosomal sequences while in utero, written in the DNA but suspended and dormant. This has been dubbed the 'X Chromosome' and is detectable via DNA tests. It was this '24th Chromosome' that Dr. Essex identified in his 19th-century magnum opus, 'On Mutants'.
The triggering event for most mutants is not birth or trauma, but the hormones of adolescence. Typically this means a mutant is between eleven and thirteen when their powers first manifest. For most mutants this is frightening and unsettling; for some it is terrifying. Powerful mutant children have accidentally cost lives and destroyed property while unable to control their power. This has created a strong anti-mutant sentiment in much of America as certain groups create a distinction between the larger metahuman community and the emergent mutants.
Mutant powers run the gamut from minor to extraordinary. A rough catagorization of their powers follows Greek conventions. Alpha mutants typically have extraordinary powers. Many Beta mutants might have unique or potent abilities, but for whatever reason they're very limited in scope and application. Gamma mutants typically have powers deemed of little use, but mostly are divided based on their gross physical deformities.
A handful of mutants have been classified as 'Omega-Level'. These individuals have the power to reshape the face of the world-- even the cosmos themselves.
Several pieces of legislation have been passed specifically targeting metahumans, and mutants in general. The Mutant Felon Relocation Act is one of the most prominent ones. The 2007 NDAA budget included provisions for arming and constructing MkIII Sentinels. Luthor Industries secured the primary contract for producing these machines. After a clash between mutants over a nuclear-armed base in 2012, hasty legislation was passed through Congress authorizing the DEO to use Sentinels for widespread peacekeeping and meta detention. This legislation was repealed in 2018 with an amendment to the Cuba Arms Treaty.