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Mutations – Types and Theory of Evolution

Grade 12
Jun 5, 2023

Introduction of Mutations

The term mutation refers to changes in genetic material; not all mutations are harmful. Mutations can occur randomly or spontaneously.
Mutations occur when the bases of DNA or RNA sequence are changed. This often occurs in DNA replication.
This lesson will help to explore and understand different types of mutations.


It covers only those changes which alter the chemical structure of the gene at the molecular level. These are commonly called gene mutations or point mutations.

Mutations is a sudden change in chromosomal DNA.

From where do the new genetic traits come from?

 For example, how can a white-eyed fruit fly be identified in a pure culture of red-eyed flies?


Or how can a short-legged sheep appear in a population of sheep with legs of normal length?

Mutation Theory of Evolution

Hugo de Vries worked on the genetics of the primrose plant (Oenothera lamarrkiana). Hugo de Vries noticed that several new traits appeared in the offspring of the plants. He observed the cause of the new traits to be permanent changes in the genetic material. Such changes are now called mutations.

primrose plant (Oenothera lamarrkiana)

Types of Mutations

Type of mutations – Gene mutations and chromosomal mutations

Point Mutations:

It is a mutation of a single base pair that can be replaced by another base pair, for example, sickle cell anemia. Mutations are caused naturally by the radiation which constantly enters the earth’s atmosphere from the cosmos. For example, gene mutations are caused when the sex cells (gametes) of the organisms are exposed to X-rays, gamma rays, cosmic rays, and ultraviolet rays. Exposure to radiations of certain chemicals called mutagens can change nucleotides within DNA molecules

 point mutation

Chromosomal Mutations

Mutations that involve a change in the structure or number of chromosomes are called chromosomal mutations. 


Structural changes in the chromosomes are caused by radiation, chemicals, and also by some viral infections. During cell division, changes occur in the structure of chromosomes.

A piece of chromosome that contains one or more genes can be deleted or moved to a different location on the same chromosome or even to a different chromosome. Such rearrangement of the chromosome has effects on the genes.

  • Deletion – When a part of chromosome is left, deletion occurs.
  • Duplication – When a part of chromatid breaks or attaches to another chromatid, duplication occurs.
  • Inversion – When a part of chromosome breaks or reattaches, it is called an inversion.  
  • Translocation – When a part of chromosome breaks or is added to the other chromosome, a translocation occurs.
chromosomal mutation


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