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Mutation Theory of Evolution and Types

Grade 8
Aug 16, 2023


Cell is the basic unit of living organisms from bacteria to humans all are made up of cells, which contain a nucleus and the nucleus contain DNA


Mutations is a sudden changes in chromosomal DNA., They cover only those changes that alter the chemical structure of the gene at the molecular level. These are commonly called gene mutations or point mutations. 

From where do the new genetic traits come?

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 Vvries 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)

  Fig. Nno 1.1  primrose plant (Oenothera lamarrkiana).

Types of Mutations 

Type of mutations – Gene mutations and chromosomal mutations 

1. Gene Mutations

DNA makes genes and genes code for proteins, influencing various traits, not all the genes code for proteins, and not all genes are turned on.

Therefore, when a mutation in DNA occurs, it is a change in one or more DNA bases takes place, then different proteins are produced which affect an organism’s traits.

  • Example: A fruit fly’s DNA faces mutations; it may include-
  • Substitution is the wrong base is matched;
  • Insertion means an extra base or other bases are added in;
  • Deletion can occur means a base is removed. So, three types of gene mutations are substitution, insertion, and deletion.

2. Chromosomal Mutations

When mutations occur at the level of the chromosome, it is called chromosomal mutation. Chromosomes are made up of DNA and protein,  for example – The human chromosome number is 46; 23 from an egg cell and 23 from a sperm cell. Similarly, the fruit fly has 8 chromosomes, 4 comes from an egg cell and 4 comes from the sperm cell.

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

Fig. no 1.2 point mutation 

Chromosomal mutations  

Mutations that which involve a change  in the structure or number of chromosomes are is 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 which contains one or more genes, it can be deleted or moved to a different location on  the  same chromosome or even to a different chromosome, Such rearrangement of the chromosome have 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 other another chromatid, duplication occurs. 
  • Inversion – When a part of chromosome breaks or it reattaches, it is called as inversion.  
  • Translocation – When a part of chromosome breaks or it is added to the other chromosome, a translocation occurs. 
chromosomal mutation

Fig no 1.3 chromosomal mutation


  • A mutation is any change in DNA sequence; it is a heritable change. 
  •  The mutation also leads to variations. 
  • Mutation word was given by Hugo de Vries.
  •  De Vries studied mutations in the plant Oenothera lamarckian and proposed the mutation theory of evolution. 
  • Type of mutations – Gene mutations and chromosomal mutations. 
  • Mutations that occur due to change in a single base pair of DNA are called point mutations, for example, sickle cell anemia.


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