What are genes?

Genes are specific segments of DNA that contain the instructions for building proteins, which perform virtually all the functions in living organisms. Think of genes as individual recipes in the complete cookbook of life that is your genome. Each gene consists of a particular sequence of DNA bases (the chemical letters A, T, G, and C) that spells out instructions for making a specific protein or set of related proteins. Humans have approximately 20,000-25,000 genes distributed across 23 pairs of chromosomes, though genes account for only about 2% of total DNA—the remaining DNA includes regulatory sequences that control when and where genes are activated, as well as regions whose functions are still being discovered.

The process by which genes direct protein production involves two main steps: transcription and translation. During transcription, the gene's DNA sequence is copied into a messenger RNA (mRNA) molecule inside the cell's nucleus. This mRNA then travels out to the cytoplasm, where translation occurs ribosomes read the mRNA sequence and assemble amino acids in the precise order specified by the gene to build a protein. Different genes produce different proteins by specifying different amino acid sequences. For example, the gene for insulin contains instructions for making the insulin protein that regulates blood sugar, while the hemoglobin gene encodes the protein that carries oxygen in red blood cells. Some genes also produce RNA molecules that have functions other than coding for proteins, such as ribosomal RNA and transfer RNA involved in translation.

Genes determine inherited traits because we receive copies from both parents—one version (allele) from our mother and one from our father for each gene. Some traits are controlled by single genes (like blood type or certain genetic disorders such as sickle cell disease), while most characteristics result from the combined effects of multiple genes interacting with environmental factors (like height, intelligence, or susceptibility to diseases). Variations in gene sequences between individuals—whether different alleles of normal genes or mutations—account for human genetic diversity and can influence everything from physical appearance and disease risk to how we metabolize medications. Understanding genes has revolutionized medicine through genetic testing, gene therapy, personalized medicine, and our comprehension of inherited diseases. Ongoing research continues to reveal how genes interact with each other and the environment to influence development, health, behavior, and the incredible diversity of life on Earth.