in Heredity and Variation by

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  1. A change in the sequence of the organism's genome, give rise to different forms of a gene is known as "Mutation".
  2. The change in a specific gene in an organism is called "Gene Mutation".
  3. In gene mutation, the substitution of a base pair for another or deletion/addition of a base pair called as "Point Mutation".
  4. Point mutation is also known as Substitution mutation, that generally results during replication.
  5. There are two types:
    1. TRANSITION MUTATION: in which substitution of pyrimidine done by the other pyrimidine molecule and the same for purine.
      Examples: G by A ; A by G and C by T; T by C
    2. TRANSVERSION MUTATION: in which purine is substituted by pyrimidine or pyrimidine is substituted by purine.
      Examples: G by T; G by C; A by T; A by C; T - A; A by G; C by G

(Here: A: Adenine, G: Guanine; C: Cytosine; T: Thymine)