Mutant:Etymology

Although not all mutations have a noticeable phenotypic effect, the common usage of the word mutant is generally a pejorative term only used for noticeable mutations.Previously, people used the word sport (related to spurt) to refer to abnormal specimens. The scientific usage is broader, referring to any organism differing from the wild type.

Mutants should not be confused with organisms born with developmental abnormalities, which are caused by errors during morphogenesis. In a developmental abnormality, the DNA of the organism is unchanged and the abnormality cannot be passed on to progeny. Conjoined twins are the result of developmental abnormalities.
Chemicals that cause developmental abnormalities are called teratogens; these may also cause mutations, but their effect on development is not related to mutations. Chemicals that induce mutations are called mutagens. Most mutagens are also considered to be carcinogens