Genes interact with the environment to confer traits. While the presence or absence of a gene can potentially confer a given trait, environmental factors also play a role in determining traits. Our physical characteristics are a combination of genetic and environmental factors. A child with a hypothetical tallness gene, for example, would not necessarily grow taller than a child without the gene; the child with the tallness gene would also require adequate nutrition to fuel the extra growth. Rather than thinking of genes as determinants of physical characteristics, they should be regarded a potentials or predispositions for characteristics.

The ability to modify characteristics of cells is similarly limited by biological and physical constraints. Some cells are rapidly replaced, meaning that induced changes will be quickly lost. Other cells are dormant, precluding their potential to express modifications. Furthermore, biology is very complicated. Unlike fields such as industrial chemistry or engineering in which applications are developed from well-characterized principles, biotechnology is on the leading edge of molecular biology research and it can be difficult or impossible to foretell the outcomes of manipulations; they can have unforeseen consequences.

Experiments must be performed because it is not possible to fully predict the outcome of procedures. Scientists must perform experiments and observe their results to continually refine theories and develop functional applications. This is why biotechnology research is so complex, time consuming, and fraught with setbacks and disappointment.