deleterious

Deleterious is an adjective meaning causing harm or damage. In everyday language it describes something harmful or detrimental to health, well-being, or success. In scientific contexts, the term emphasizes negative effects on biological fitness or ecological systems.

In genetics, a deleterious mutation or allele reduces an organism's fitness, lowering reproductive success or survival. The impact depends on dominance, environment, and genetic background. In population genetics, deleterious alleles arise by mutation and are removed by natural selection; their persistence is influenced by mutation rate, genetic drift, and linkage to other variants.

In ecology, deleterious interactions can occur within communities, such as a species that suppresses others, reduces productivity, or increases vulnerability to disease.

In medicine and pharmacology, deleterious effects refer to adverse outcomes from drugs or treatments, or from genetic variants that cause disease. The term is used in risk assessment, clinical trials, and adverse event reporting.

Etymology and usage: the word derives from Latin deletere meaning to destroy, entering English in the early modern period. It is often contrasted with beneficial or neutral in discussions of mutations, adaptations, and environmental changes.

See also: harmful, detrimental, adverse, pathogenic, toxic.