I did a little research and it wasn't easy, but I think I finally understand what Foucault meant by "genetic". He explained how human beings are being conditioned to perform essentially like machines, with really very little emotional interaction at all between the ruling powers and their subjects, 'distancing' those who dominate us from any blame we might feel toward them about being compelled to submit to their rules. Foucault's theory covers not only the current criminal justice system, but education and general citizenship as well.
People are being systematically conditioned to be as self-governing as possible, with what I see as paranoia being the motivating factor: we're never completely sure whether or not we're being watched, we're constantly being judged, and hence subjected to grading/rating of our performance with the possibility of mandatory remedial and/or rehabilitative programming, by those who officially hold authority over us, if we should happen to step out of line. So fear and intimidation are the real motivators. And the goal is to have us serve their best interests: work, stay out of trouble, pay taxes, spend money, etc.
Each one of us is treated like and expected to behave as a machine within a far bigger social structure: the collective human 'machine', which may be managed effectively utilizing just four simple principles:
cellular - the relations between each 'body' (i.e each person is a cell). These must be classified and distributed wherever and however they are needed, for maximum extraction of forces and time. Although human, we must nevertheless be as efficient as any other machine.
organic - the things living bodies (people, "cells") need for sustenance: food, water, medicine, a bed to sleep in, etc. In other words, the basic necessities needed to keep us all functioning properly.
genetic - Foucault must have meant genetic in the second meaning of the word,
relating to origin; arising from a common origin.
...as it is the only way that it makes any sense to me. Because the human 'machine' becomes more powerful with the increase in number of cells (individuals), the bigger the workforce, the more productivity and more gross national product to be gained. So in order to become more powerful, it is necessary to "constantly accumulate" the "genetic" material (i.e. "origin") or labor pool: human beings. So "constant genetic accumulation" simply means they need to get more and more people to cooperate by conforming to their system. More cells equals a bigger, more powerful machine.
And last, but not least:
combinatory individuality - this is the illusion of being an individual when in fact we have merely conformed to the standards of those who have authority over us. Combinatory individuality is the ultimate goal. We may have begun our lives as individuals, but with consistent hierarchical surveillance, normalizing judgement, and regular examinations -- together we all eventually become subsumed within the collective entity: "Welcome to the Machine."
My sources were mainly Youtube, Wikipedia, and Foucault As Educator, by Stephen J. Ball (c.2017)