determinant
n.n. a substance that causes a specific change in a living system. In biology, it is often a chemical that tells a cell what to do or how to grow.
n. a substance that influences or determines a particular biological process or outcome. Often refers to a chemical signal that regulates cellular activity or developmental pathways.
The growth hormone is a key determinant of height.
Researchers identified a specific protein as the primary determinant of how quickly the cells divide during the early stages of development.
While genetics provides the blueprint, environmental factors such as nutrition and stress serve as the primary determinants of how those genes are expressed in the final phenotype.
Borrowed from French déterminant, equivalent to determine + -ant.