Lethal and sub lethal inheritance 2-1

Lethal genes cause death of the organism at embryonic stage shortly after birth or at a later age. The mutation in critical genes essential for growth and development. It may be recessive dominant or condition dependent based on genetic expression.

L Cuenot 1905 discovered.

Dominant lethal

Recessive. may be silent or mild inconvenience when heterozygous but lethal when homozygous. 

Conditional lethal. Genes that are fatal in some environments. 

Gametic lethal. that lead to in viability of gametes and made them incapable of fertilization. 

Sub lethal genes.
Natural selection favours a gene. 

Some persist due to selective advantage like G6PD and sickle cell anaemia advantage against malaria. Dhobzansky.

Muller argues. Modern medical practices are increasing there propagation like phenylketonuria PKU disease.