Principles of Plant Breeding (2+1)

Types of Mutations

Types of Mutations
Transition

• Mutation by transition entails the conversion of one purine base to another purine (or a pyrimidine to another pyrimidine) When a purine is replaced by purine. E.g. Adenine is replaced by guainine or pyrimidine by pyrimidine. E.g. Thymine is replaced by cytosine.
Transversion

• A transversion involves the substitution of a purine by a pyrimidine and vice versa.
  
• Pyrimidine is replaced by purines. A to Z, A-C, G-C G-T Transition, Trans version are relatively also deleterious, but base substitution may generate such codon that codes for any amino acid (sense codons) whenever the nonsense codon is produced it acts on terminator of the poly peptides changes.
Base addition/ deletion

• A variety of alkylating agents (E.g., sulfur and nitrogen mustards) can act on the DNA molecule, reacting mainly with guanine (G) to alkyl ate and remove it from the DNA chain.
  
• The missing spot may be occupied by any one of the four bases to create mutations, usually by transition.
  
• Acridine is also known to express its mutagenic effect through the addition of deletion of bases.
  
• An insertion of one or more bases in a DNA molecule is called based addition.
Frame shift mutation

• Insertion-deletion mutations may cause significant changes in the amino acid composition of a protein and hence its function. E.g. GAG-CCG-CAA-CTT-C (corresponding to Glu-Pro-Glu-Leu) may be altered by a deletion of G that shifts the reading frame to the right by one nucleotide to produce AGC-CGC-AAC-TTC (corresponding to Ser-Arg-Asi-Phe).