There is no single "gay gene." Instead, sexual orientation is influenced by many genes and is therefore a(n) _____ characteristic.

The correct term to fill in the blank is "polygenic."

Explanation:

Sexual orientation is a complex trait that is believed to be influenced by multiple genetic and environmental factors rather than being dictated by a single gene. This means that various genes contribute to the development of sexual orientation in individuals, making it a polygenic characteristic. Research in genetics shows that traits like sexual orientation often result from the cumulative effects of many genes, each with a small impact, along with interactions with environmental factors. This complexity indicates that genetics is intertwined with other biological, social, and personal factors, creating a rich tapestry of influences on human sexuality. Therefore, the term "polygenic" appropriately describes the multifaceted nature of sexual orientation.