Dictionary.com
definitions

lethal gene

noun Genetics.
  1. a gene that under certain conditions causes the death of an organism.

Origin of lethal gene

First recorded in 1935–40
Also called lethal factor, lethal mutation.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
lethal mutation in Medicine

lethal mutation

n.
  1. A mutant trait that leads to a phenotype incapable of effective reproduction.

lethal gene

n.
  1. A gene whose expression results in the death of the organism.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.