Relating to or denoting an allele or chromosomal abnormality that impairs the viability of most of the individuals homozygous for it.
- ‘A chief difficulty in arguing for macroevolution by mutations is the fact that most expressed mutations are either lethal or semi-lethal.’
- ‘Pokey (pok), a sex-linked recessive semi-lethal gene in Tribolium castaneum has been described.’
- ‘Some of the genes that gives the mouse its common colours or markings also makes the mouse sick, or unfit to live. These genes are called semi-lethal or lethal.’