Gene expression is the process by which the information encoded in a gene is copied into a complementary RNA molecule to direct the production of a functional product, typically a protein, but sometimes a functional RNA (like tRNA, siRNA or rRNA).
Human genetic information primarily is contained within chromosomal nuclear genes, inherited from both parents, but is also present in mitochondrial genes inherited from the maternal line and now known also from the fraternal line
The formation of the gene product gives the gene control over structure and function.
The gene products define the transmission of hereditary characteristics.
Genes act in combination with an organism's environment to influence development.
It allows cells to respond to their environment.
It determines cell function and identity (e.g., muscle cells express muscle proteins; neurons express neurotransmitter-related genes).
Abnormal gene expression can lead to diseases, including cancer.