The basic unit of heredity is the gene. A gene is a segment of DNA that contains the information needed to produce a functional product, usually a protein or a non-coding RNA. Regulatory sequences control when, where, and how much of the product is made.

Genes are arranged linearly on chromosomes. Alternative splicing and multiple regulatory elements allow one gene to generate several products. Mutations within a gene can alter or abolish its function, producing genetic variation or disease.

The human genome contains roughly 20,000 protein-coding genes plus many non-coding genes. Annotation projects continually refine gene boundaries and functions. Understanding individual genes remains central to explaining traits, diagnosing disorders, and designing targeted therapies.

• Segment of DNA encoding a functional product
• Includes coding and regulatory regions
• Located at a specific chromosomal locus
• Can produce proteins or non-coding RNAs