Once again, what part of reasonable doubt do you not understand? If one in 100,000,000 is a chimera, I'll stick with DNA as a means to determine reasonable doubt - unless you'd rather several hundred men stay in jail so that we might catch that one chimera.
IF
1) LAST TIME I CHECKED (a year or two ago), NO ONE KNOWS THE INCIDENCE.
THEY ASSUME IT'S RARE.
2) BUT EVEN IF they PROVED it rare in the GENERAL population of humans--
That would not be good enough.
They would need to prove that being a human chimera does not make one more prone to CRIMINAL BEHAVIOR (a reasonble suspicion, given how a chimera's DNA is all mess up)--
And that would make the frequency of chimerism among prisoners higher.