Agene cannot react chemically and form a trait without the proper molecule enzyme substrate chromosome

A gene cannot react chemically to form a trait f the proper enzymes are not present. The formation of a trait from the gene is dependent on the expression of the gene. The gene expression is a process which involves the help of the various enzymes. The absence of any of these essential enzymes will make it impossible for the gene to express the trait for which it is coded.

Hence, the answer is 'enzymes'.