A large proportion ofgenesin an individual’s genome are essential for survival. Occasionally anallelefor an essential gene can become non-functional through a mutation. Because the gene is essential, these individuals might fail to develop past fertilization, die in utero (in the uterus), or die later in life, depending on what life stage requires this gene.
inheritance pattern in which an allele is only lethal in thehomozygousform; theheterozygotemay be normal or have some altered non-lethalphenotype.
inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after the reproductive age.