What can regulate the functioning of a gene? choose the best answer.

external environment
internal environment
homeostasis
internal and external environment

The right answer is internal and external environment.

Influence of the internal environment:

In prokaryotes as in eukaryotes, the genes are regulated mainly at the stage of transcription initiation, most often by proteins capable of activating or inhibiting the functioning of the gene. The activators still function by recruitment of RNA polymerase but also, in eukaryotes, protein complexes responsible for the initiation of transcription. This regulation is done according to the needs and the function of the cell.

Influence of the external environment:

Our environment has an influence on our genome by so-called epigenetic modifications. For example, with identical genetic heritages, two twins may evolve differently depending on their respective environments. Individuals, and consequently their genes, are indeed subject to many environmental factors: diet, diseases, drugs and toxins, stress, place & lifestyle, which can modify their cells as much as their DNA.