Principles of Genetics and Breeding

3.1.6 Lethal genes

A gene whose phenotypic effect is sufficiently drastic to kill the bearer is called lethal gene. Death from different lethal genes may occur at any time from fertilization of the egg to advanced age.

• Lethal genes may be dominant, incompletely dominant or recessive.
• The fully dominant lethal gene kills the carrier individual both in homozygous and heterozygous conditions.
• Completely dominant lethal genes usually cause death of the zygote later in embryonic development or even after birth or hatching. No individuals will attain the age of reproduction.
• Lethal genes arises occasionally by mutation from normal allele. The individual with a dominant allele die before they can produce the progeny. Therefore the mutant dominant allele is removed from the population in the same generation in which it arose.
• The recessive lethal allele kills the carrier individual only in homozygous condition.
• Certain lethal genes produce certain disorder to the individuals but do not destroy the individual completely. They handicap but do not destroy. Such genes are called semi lethal genes or sub lethal genes or subvital genes.