Mutation-Definition, Major Classes, and Types-Discussed!

Mendelian segregation never produces new character but re­sults in only redistribution of genes.

Darwin was aware of these sudden changes and called ‘sports’ while Bateson described as ‘discontinuous variation’ and stated that they were of general oc­currence.

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Hugo DeVries (1901) gave the name ‘mutation‘ to these sud­den discrete changes. He worked on evening Primerose plant (Oenothera lamarkiana).


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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