The term ‘lethal’ in genetics is applied to those changes in the genome of an organism that produces effects severe enough to cause death. The fully dominant lethal allele kills the individual both in in its homozygous and heterozygous conditions. The individuals with dominant lethal allele die before they can produce progeny. Therefore, the mutant dominant lethal allele is removed from the population in the same.
Lethal alleles in plants
In snapdragons three types of plants occur
Green plants (green due to the presence of chlorophyll)
Yellowish green plants ( due to the presence of carotenoids)
White plants ( due to the absence of chlorophyll)
Homozygous green plants have genotype CC, cc are white plants which do not have chlorophyll. The yellowish green plants also called golden or auria plants, have the genotype Cc.
When two auria plants are crossed, albino plant dies at lacks chlorophyll , the ratio is modified into 2:1, the homozygous recessive genotype being lethal.
Similar lethal gene controlling the amount of chlorophyll is found in Zea Mays. The recessive allele g controls the chlorophyll content and exhibits its effect in homozygous and heterozygous condition (gg) combination is lethal and so the ratio is modified to 2:1.
Lethal alleles in animals
“Yellow” lethal in mice – In mice, an incompletely dominant allele Y for yellow coat has been found lethal in homozygous condition. This condition of yellow lethal of mice was first reported by Cue’not.