Mutation Breeding

Mutations are defined as heritable changes in structure number of genes or chromosomes. Mutations can be natural (spontaneous) or induced. Many natural mutations are recorded. But, stability of mutant expression needs a thorough testing over generations, as many mutants have tendency to revert to normalcy.

Mutations can be induced by what are known as mutagens. Several mutagens like X-rays, UV - rays, g - rays and some chemicals have been extensively used for inducing mutations.

Chromosomal Mutation

They are mutation involving change in number or structure of chromosomes. Change in number of chromosomes induced by mutagens can lead to aberrant gametes, which when fuse with normal gamete lead to aneuploid zygotes. Changes in chromosomal structure by mutation are brought about in four different ways

• Deletion: A fragment of chromosome is lost

• Duplication: A piece of chromosome joins a homologous piece of other chromosome

• Inversion: A lost piece of chromosome rejoin same chromosome in reverse orientation.

• Reciprocal Translocation: A piece of chromosome join a non homologous chromosome reciprocally.

Deletions and duplications occur during errors in crossing over, while other two mutations occur during later stages of cell division.

Such chromosomal mutations either lead to loss of genes or relocation of genes. While loss of some genes can lead to many drastic phenotypic changes, even dislocation of genes also lead to substantial modification of genetic and morphological features. Most mutations lead to useless mutants. Mutagens may bring about mutations. But, it is difficult to produce only desirable mutations. Thus selection - a very extensive one - is always necessary to be followed after mutations. Mutants may also be used for crossing to produce many desirable traits during the process of breeding.

Success in using mutation as a breeding method has been reported in some crops like barley, wheat, rice and groundnut.