Some genes have serious effects that the organism is unable to live. Alleles whose effects is to kill bearers of certain genotypes are called lethal genes.
Lethal gene were first discovered by Cuenot.
- In absolute lethality individual die in embryonic stage. (ex:Yellow fur in mice)
- In sublethality individual dies before reproductive maturity. (Sickle cell anemia)
|Sickle cell anemia|
- In delayed lethality individual dies after sexual maturity.
Lethal effect of an allele may be dominant or recessive.
- Dominant lethals- Whose lethal effects occur in heterozygous individuals.
Epiloia in humans is an example for dominant lethal gene. If the lethal effect is dominant, all the individuals carrying the allele will die and the gene cannot be transmitted to the next generation.
- Recessive lethals- If lethality is due to homozygousity for a recessive allele, the allele is called a recessive lethal. The phenotypic ratio is always converted from 3:1 to 2:1.