lethal gene

A mutant allele that results in the death of an organism. The mutation commonly takes the form of a small chromosomal deletion, so that the genetic code for a key protein is missing or   disrupted.   Such   mutations   do   not necessarily take effect at fertilization but may manifest themselves at any stage of development. The chlorophyll-less mutant (chl^—) of barley, which is typically recessive, only shows its lethal effects after the food reserves in the germinating seed have been used up.