Types of Variations –

Somatogenic and Blastogenic Variation

• Changes in somatic parts of the body are somatic variations e.g. wrestler’s muscle, circumcised penis of muslims, etc., not inheritable, hence have no role in evolution.

• Blastogenic variations are the changes at germinal cell level or in the genotype or gene patterns, these are inheritable and hence form the basis for evolution.

2. Continuous and Discountinuous Variation

• Continuous variations are small, gradual changes e.g. changes in color, size, shape, body weight etc.

• The discontinuous variation are the discrete and sudden, without any intermediate stage or gradations.

• This is qualitative (substantive) when related to color, shape and size e.g., Ancon sheep in Seth Wright’s farm quantitative (meristic) when related to the number of parts e.g. – hexadactyli, single kidney, single horn etc.

3. Determinate and Indeterminate variation

• Determinate variation are adaptive, selective and of definite evolutionary line, also called as orthogenic variation; controlled by strong genes, sometimes, it may become deleterious beyond the limit of its usefulness.

• Indeterminate variations have no evolutionary line, it is sudden and nondirectional.