 However, because flow cytometry-based sperm sorting often uses fluorescent dyes that often stain DNA, the safety of this technique in human reproductive medicine is a matter of scientific discussion.However, flow cytometry is the only currently used technique able to determine the sex of future progeny by measuring DNA content of individual sperm cells.It evaluates if they contain the larger X chromosome (giving rise to a female offspring) or smaller Y chromosome (leading to male progeny).