Mutation
- 1. Mutation Prof. Harshraj. S. Shinde K. K. Wagh College of Agril. Biotech, Nashik. India
- 2. Introduction • 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 variant • Factor or agents causing mutation are known as mutagens • Mutation which causes changes in base sequence of a gene are known as gene mutation or point mutation
- 3. 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
- 4. Characteristics of Mutation • Generally mutant alleles are recessive to their wild type or normal alleles • Most mutations have harmful effect, but some mutations are beneficial • Spontaneous mutations occurs at very low rate • Some genes shows high rate of mutation such genes are called as mutable gene • Highly mutable sites within a gene are known as hot spots. • Mutation can occur in any tissue/cell (somatic or germinal) of an organism
- 5. Classification of mutation • Based on the survival of an individual 1. Lethal mutation – when mutation causes death of all individuals undergoing mutation are known as lethal 2. Sub lethal mutation - causes death of 90% individuals 3. Sub vital mutation– such mutation kills less than 90% individuals 4. Vital mutation -when mutation don’t affect the survival of an individual are known as vital 5. Supervital mutation – This kind of mutation enhances the survival of individual
- 6. • Based on causes of mutation 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. use of induced mutation for crop improvement program is known as mutation breeding. Eg. X- rays causing mutation in cereals
- 7. • Based 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. • Based on direction of mutation 1. 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
- 9. • Type of trait affected 1. Visible mutation- Those mutation which affects on phenotypic character and can be detected by normal observation are known as visible mutation 2. Biochemical mutation- mutation which affect the production of biochemicals and which does not not show any phenotypic character are known as biochemical mutation
- 10. Chromosome Mutations • May Involve: –Changing the structure of a chromosome –The loss or gain of part of a chromosome
- 11. Chromosome Mutations • Five types exist: –Deletion –Inversion –Translocation –Nondisjunction –Duplication
- 12. Deletion • Due to breakage • A piece of a chromosome is lost
- 13. Inversion • Chromosome segment breaks off • Segment flips around backwards • Segment reattaches
- 14. Duplication • Occurs when a gene sequence is repeated
- 15. Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosomes
- 16. Translocation
- 17. Nondisjunction • Failure of chromosomes to separate during meiosis • Causes gamete to have too many or too few chromosomes • Disorders: – Down Syndrome – three 21st chromosomes – Turner Syndrome – single X chromosome – Klinefelter’s Syndrome – XXY chromosomes
- 19. Types of Gene Mutations • Include: –Point Mutations –Substitutions –Insertions –Deletions –Frameshift
- 20. Point Mutation • Change of a single nucleotide • Includes the deletion, insertion, or substitution of ONE nucleotide in a gene
- 21. Point Mutation • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene
- 22. Frameshift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly
- 24. Reference Book Genetics By B. D. Singh (Kalyani Publications)