The short story is that there had been found a statistical correlation between certain gene variants and the kind of behavior called "criminal".
Depending on their agenda, people referred to these gene variations as "bad", "defect" or simply "criminal" genes. However the information about gene variations had to be correlated with such things as neglect, abuse and malnutrition in childhood before a real statistical correlation could be found.
The public discussion addressed the actual scientific validity of these findings, but, the debate was more heated regarding what kind actions should be taken, if any*:
Should children with such genes be singled for special treatment so that the gene was not "triggered"?
Should they be incarcerated before they could go bad and cause harm?
Should they simply be "put down" like mad cows?
Should adults with such genes be allowed to produce children in the first place?
Or should we simply ensure that general good living conditions for every little girl and boy was the accepted norm?
For my money, I figured that they should have checked the genes of people who become dictators like Ronald Rexona and megalomaniacs like his evil companion, Mr. Snarly. Perhaps they could have decided not to ever let such people have the power of life and death over nations and even the entire Third Galaxy.
I know that maybe sounds a bit farfetched or even slightly crazy, but the fact is Rexona was pretty good at clearing out underbrush with a bush-whacker and Mr. Snarly, although not a first-rate telephone linesman, he wasn't bad at the job either.
* Unlike our own world, there had been a terrible history in the Third Galaxy of violence, pogroms and even extermination of people of the wrong race or with "tainted" or "inferior" blood.