What technique do scientists in GATTACA use to design preferred traits?

In GATTACA, the technique used to design preferred traits in individuals is selective breeding. This method involves choosing specific individuals to reproduce based on desired genetic qualities, effectively ensuring that offspring inherit traits valued by society, such as intelligence, health, and physical abilities. Through extensive genetic manipulation and screening, scientists create individuals who fit predefined genetic profiles, showcasing the potential of selective breeding to produce 'designer' humans.

Selective breeding is depicted as a crucial societal practice in the film, allowing parents to make choices about their children's genetic make-up before birth. This concept is closely tied to the ethical implications and the societal divide between genetically engineered individuals and those conceived naturally, contributing to the film's themes regarding genetic discrimination and identity.

The other options, while related to genetic manipulation, serve different purposes and are not the primary technique highlighted in GATTACA. Gene therapy aims to treat or prevent diseases by altering genes in a person's cells, while cloning involves creating a genetic copy of an organism rather than enhancing specific traits. CRISPR technology is a modern gene-editing tool that can precisely modify DNA, but in the context of the film’s narrative, selective breeding remains the central method.