• It is the phenomenon of one gene affecting more than one character.
• Eg: Sickle cell anemia, white eye gene in Drosophila

a) Lethal gene action:

• Some time , the pleiotropic gene effect produces various abnormal ability in phenotypic feature which are collectively called syndromes.
• When the pleiotropic gene cause further death of the individual then it is called lethal gene.
• This lethal gene is either in a homozygous condition (dominant)or homozygous recessive condition.
• It is of following types: Dominant lethal. Recessive lethal, conditional lethal, Balanced lethal and gametic lethal.

b) Semi lethal gene action:

• < 10% individuals survive.
• Eg: xantha mutants.

c) Vital gene action:

• Don’t affect the survival of the individuals.
• Neither enhance nor reduces the viability.

d) Sub vital gene action:

• Reduces viability.
• Kill less than 90% individuals .
• Eg: Mutant species.

e) Super vital gene action:

• Enhance the survival of the individual.
• Eg: disease resistance , insect resistance and other resistance.