Mutation legged sheep was discov­ered by English

Mutation may be defined as sudden heritable change in a gene due to change in sequence of nucleiotides which alter the phenotype of an individual, e.

g. Short legged sheep was discov­ered by English farmer Wright (1791). Morgan (1910) studied mutation in Drosophila and reported white eyed mutant in red eyed flies. Major classes:

1. Chromosomal aberration-

Change in structure and number of chromosomes.

2. Gene mutations-

Change in single gene. Types of mutations:

1.

Germinal mutation:

Change in reproductive cells (sperms and eggs) of the individual take place. The change may take place in gamete (gametic) or zygote (zygotic).

2. Somatic mutation:

Change in somatic vegetative cells. How­ever, they are not hereditary they perish with the individual in which they occur.

3. Reverse mutation:

The mutated gene undergoes change i.e.

back to the normal, hence they are also called reverse or back mutations. They are rare and less frequent than normal muta­tions.

4.

Spurious mutation:

When recessive genes appear phenotypically by the crossing over it is known as spurious mutation. They are generally hidden mutations, e.g.

Pink eye color in Drosophila.

5. Anomozygous mutation:

Changes occur due to structural variations in the chromosome i.

e. chromosomal aberrations or change in chromosome number (heteroploidy).

6.

Biochemical mutation:

They affect biochemical process i.e. loss of ability to synthesize vitamins and amino acids. They are studied in Neurospora by Beadle and Tatum.

7. Lethal mutation:

They cause death of organisms similarly loss or alternation in essential function of an organism.

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