Mutation

Mutation: Introduction and types

1. MUTATION By Rachana Tiwari Assistant Professor

2. CONTENT Introduction Causes of Mutation Types of mutation Effect caused by mutation Conclusion Reference

3. INTRODUCTION A  mutation  is a change in a DNA sequence.  Mutations  can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses. Sudden heritable change in genetic material or character of an organism is known as mutation . Individuals showing these changes are known as mutants An individual showing an altered phenotype due to mutation are known as v ariant . Factor or agents causing mutation are known as mutagens Or

4. HISTORY English farmer Seth Wright recorded case of mutation first time in 1791 in male lamb with unusual short legs The term mutation is coined by Hugo de Vries in 1900 by his observation in Oenothera Systematic study of mutation was started in 1910 when Morgan genetically analyzed white eye mutant of Drosophila H. J. Muller induced mutation in Drosophila by using X- rays in 1927 ; he was awarded with Nobel prize in 1946

5. CAUSE 1 . Spontaneous mutation- Spontaneous mutation occurs naturally without any cause. The rate of spontaneous mutation is very slow eg- Methylation followed by deamination of cytosine. Rate of spontaneous mutation is higher in eukaryotes than prokaryotes. Eg . UV light of sunlight causing mutation in bacteria 2. Induced Mutation- Mutations produced due to treatment with either a chemical or physical agent are called induced mutation . The agents capable of inducing such mutations are known as mutagen. Eg. X- rays causing mutation in cereals

6. TYPES Based on direction of mutation Forward mutation - When mutation occurs from the normal/wild type allele to mutant allele are known as forward mutation 2. Reverse mutation - When mutation occurs in reverse direction that is from mutant allele to the normal/wild type allele are known as reverse mutation

7. TYPES B ased on tissue of origin 1. Somatic mutation- A mutation occurring in somatic cell is called somatic mutation. In asexually reproducing species somatic mutations transmits from one progeny to the next progeny . 2. Germinal Mutation- When mutation occur in gametic cells or reproductive cells are known as germinal mutation. In sexually reproductive species only germinal mutation are transmitted to the next generation

8. TYPES Chromosomal Mutation May Involve: Changing the structure of a chromosome Leads to either loss or gain . Five types exist: Deletion I nversion Translocation Nondisjunction Duplication

9. CHROMOSOMAL MUTATION DUPLICATION Translocation

10. GENE MUTATION Point Mutation A  point mutation  is a change in a single  nucleotide  in DNA. This type of  mutation is usually less serious than a  chromosomal alteration An example of a  point mutation  is a  mutation  that changes the  codon  UUU to the  codon UCU. Point mutations can be silent, missense, or nonsense mutations, as shown in the following table. The effects of point mutations depend on how they change the  genetic code .

11. POINT MUTATION

12. TYPES OF POINT MUTATION  Point Mutation Types Type Description Example Silent mutated codon  codes for the same amino acid CAA (glutamine) → CAG (glutamine) Missense mutated codon  codes for a different amino acid CAA (glutamine) → CCA (proline) Nonsense a mutated codon  is a premature stop codon CAA (glutamine) → UAA (stop) usually

13. FRAME SHIFT MUTATION A  frameshift mutation  is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA: AUG-AAU-ACG-GCU = start-asparagine-threonine-alanine Now assume that an insertion occurs in this sequence. Let’s say an  A   nucleotide  is inserted after the start  codon AUG.  Then the sequence of bases becomes: AUG-AAA-UAC-GGC-U = start-lysine-tyrosine-glycine

14. Even though the rest of the sequence is unchanged, this insertion changes the  reading frame and thus all of the codons that follow it. As this example shows, a  frameshift mutation can dramatically change how the codons in mRNA are read. This can have a drastic effect on the  protein product Another example of the  frameshift mutation due to the deletion of a  nucleotide is illustrated in the figure below. In this example, a premature stop  codon  is created by the  mutation

15. FRAMESHIFT MUTATION