in biology, any observable feature, or trait, of an organism, whether acquired or inherited. An acquired character is a response to the environment; an inherited character is produced by genes (gene) transmitted from parent to offspring (their expressions are often modified by environmental conditions). One gene may affect many characters; one character may be controlled by many genes. A character controlled by only a few genes is known as an oligogenic, discontinuous, or qualitative character; a character controlled by many genes is termed polygenic, continuous, or quantitative. A genetically controlled character may be termed dominant when its controlling genes are powerful enough to mask the effect of other genes (alleles) that control an alternative character, termed recessive.

A sexual character is one that distinguishes male from female. An organism's primary sexual characters are its reproductive organs and gametes (sex cells); an organism's secondary sexual characters include all other structural or visual differences, such as mammary glands, muscular development, plumages, and behavioral patterns, that do not figure directly in the reproductive act.