"You means..." Zhang Qin Feng was a little embarrassed after hearing what Valerian said. But from her words alone, he knows what she was mentioning. The so-called Gene Sample from Valerian's sentence is the white substances he's been offloading inside their body each time he had intercourse.
In a way he understands, Zhang Qin Feng felt a hint of medical malpractice in this apocalyptic world. It seems that the clones were sterilized during their growth stage to make sure there's no unwanted pregnancy.
Although such a setting was easily removable during their growth process, the arrangement is no longer touchable nor adjusted after many years of the autonomous program. This world will not have people capable of conceiving unless Zhang Qin Feng personally entered and took over the cloning shelter by force and resetting the machine controlling the production.