Mutation : types and features...........

Mutation types

1. Mutation 1 Submitted to , Merin Alice George Department of Botany St. Teresa’s College, Ernakulam. Submitted by , Cathy Surya Msc Botany

2. Mutation Sudden heritable change in gene or character of an organism Individuals showing mutation – mutants . Individual showing altered phenotype due to mutation – variant Factors causing mutation – mutagens Mutation that causing changes in base sequence of a gene – gene mutation or point mutation. 2

3. Mutation Term mutation coined by – Hugo de Vries Earliest record of point mutation recorded in 1791(in male lamps with unusual short legs). Scientific study of mutations started in 1910 by T.H. Morgan ( analyzed white eyed mutants in Drosophila). 3

4. Characteristics of Mutation Generally mutant alleles are recessive type, dominant type are also seen . Most mutations are harmful, but some are beneficial. Mutations are major cause of genetic variation in a population. Some genes show high rate of mutation, they are called Mutable genes. Highly mutable sites in a gene are known as hotspots . 4

5. Stages at which Mutation Occur In germinal cell – if it is before differentiation of gametes, it would influence all the individuals derived from affected gametes. If it occurs in gamete or zygote – Single individual shows mutant character. If it occurs in a cell after divisions of zygote – Only a part of the body will show mutant character. Somatic mutation or Germinal mutations. 5

6. Classification and types of Mutation Based on the method of detection of mutations. Morphological mutations Alterations in external form like colour, shape, size etc Example: Kernal colour in corn. 2. Lethal mutations Alterations that leads to death of an individual. Example: Lethal mutations in Drosophila. 6

7. Continuous… 3. Biochemical mutations Identified by deficiency. It can be overcome by adding the compound in which the mutant is deficient. Example: Mainly in prokaryotes like bacteria, fungi 4. Resistant mutations Identified by their ability to grow in the presence of an antibiotic or a pathogen. 7

8. Continuous… Based on the causes of mutation Spontaneous mutation It occurs naturally without any cause. They generally occur due to error during replication, mitosis, meiosis, etc. 2. Induced mutation Do not occur spontaneously. They are induced through various chemical and physical agents known as mutagens. Mutagens greatly enhance the frequency of mutation. 8

9. Spontaneous mutation a)TAUTOMERISM : Ability of a molecule to exist in more than one chemical form. A base is changed by the repositioning of a hydrogen atom by altering the hydrogen bonding pattern of that bases, resulting in an incorrect base pairing replication. 9

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11. Spontaneous mutation b) Depurination : Loss of Purine base (A or G) to form apurinic site. 11

12. Spontaneous mutation c) Deamination : Removal of an amine group from a base. Deamination of cytosine converts it to uracil, which will pair with adenine instead of guanine at the next replication, resulting in a base substitution. 12

13. Induced mutation Types of Induced mutagens: 1) Physical mutagens Radiation a.) Ionizing ( e.g X ray, gamma)- Based on duration and wavelength. b.) Non Ionizing ( eg. UV) – Exposure to harmful wavelength causes mutation. Temperature a.) Break the Hydrogen bond in DNA. b) Result form apurinic site or base less site . 13

14. 2) Chemical mutagens a.)Nitrous acid – change in chemical composition of bases. b.)Alkylating agents – Addition of alkyl groups c .)Base analogues - Can be substitute for purines or pyrimidines during nucleic acid biosynthesis 3) Biological mutagens Virus, bacteria etc. 14

15. Continuous… Based on tissue origin Somatic mutation Mutation occurring in somatic cells. In higher plants, somatic mutations can often be propagated by vegetative means, such as grafting or the rooting of stem cuttings. 2. Germinal mutation Mutation occurring in gametic cell or reproductive cell. 15

16. Continuous… Based on the direction of mutation 1. Forward mutation Mutation occurring from normal type allele to mutant allele. 2. Reverse mutation Mutation occurring from mutant allele to normal type allele. 16

17. TYPES OF MUTATIONS 17 Chromosome mutation Gene mutation Change in number Change in structure Base substitution Addition or Deletion of a nucleotide

18. Chromosomal mutations (structural aberrations) 18 Chromosomal aberrations are kinds of mutations produced as a result of segmental change in the chromosome. Deletion Inversion Duplication Translocation

19. Deletion Due to breakage. A piece of a chromosome is lost. Types of deletions Terminal deletions- Loss of segment from one end of chromosome. The terminal deletion is caused by a single breaks in a chromosome. 19

20. Deletion Intercalary deletion- Loss of an intercalary segment of the chromosome, leaving the ends of the chromosome intact. The intercalary deletion is characterized by two point breaks and the reunion of terminal parts. 20

21. Genetic effects of deletion Deletion involve loss of genes. The intensity of effect depends upon the number and quality of the lost genes. Large deletions may produce abnormal phenotype even in heterozygous deletion. The expression of recessive allele due to deletion of dominant alleles is –Pseudodominance (Waltzing mouse) 21

22. Inversion Chromosome segment breaks off and re attaches in the reverse direction. Two types Paracentric Inversion : Without including the centromere. Pericentric Inversion : Which includes the centromere. 22

23. Inversion in which one homologue is inverted and the other is not – heterozygous inversion . Inversion in which both homologues are inverted – homozygous inversion. In homozygous inversion normal meiosis occurs in homologous chromosomes. In heterozygous inversion, the pairing of chromosome occurs by forming a loop in the inverted chromosome. Crossing over occurring in the inversion loop of paracentric inversion, produce dicentric and acentric chromosome . 23

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25. Duplication Occurs when a gene sequence is repeated. 25

26. Genetic effects of duplication Duplications are significant in reducing the lethality caused by deletions. Duplications are important raw materials of organic evolution. The extra genes, produced by duplication, are not essential for normal development and reproduction. Sometimes accumulated mutations produce new gene that is beneficial for organism leading to speciation and evolution . 26

27. Translocation Involves two chromosomes that aren’t homologous. Part of one chromosome is transferred to another chromosomes. 27

28. Chromosomal mutation( Variation in number) Aneuploidy The abnormal condition were one or more chromosomes of a normal set of chromosomes are missing or present in more than their usual number of copies. Common among animals. Nullisomy : The loss of both pairs of homologous chromosomes – 2n-2. Monosomy: The loss of a single chromosome -2n-1 Trisomy: The gain of an extra copy of a chromosome – 2n+1 28

29. Chromosomal mutation( Variation in number) Disorders: Down Syndrome – three 21st chromosomes Turner Syndrome – single X chromosome (XO) Klinefelter’s Syndrome – XXY 29

30. Chromosomal mutation( Variation in number) Polyploidy – The condition in which the somatic cells contain more than two basic set of chromosomes. It includes triploidy , tetraploidy , pentaploidy. Common among plants. 30

31. GENE MUTATIONS 31 POINT MUTATION FRAMESHIFT Mis- sense Silent Mutation 3. Non Sense Insertion Deletion

32. Point mutation Affects only a single nucleotide of nucleic acid. Point mutations most commonly involve the substitution of one base for another. 32

33. Mis-sense mutation It is a single base mutation that replaces one nucleotide of the codon on the DNA with other nucleotides, which eventually results in coding a different amino acid in the protein. Resultant protein may be either functional or nonfunctional Example: Sickle cell anemia 33

34. Sickle cell anaemia (Missense mutation) Sickle cell disease(SCD): Is a hereditary blood disorder, characterized by an abnormality in the oxygen-carrying hemoglobin molecule in red blood cells. Humans contain two types of haemoglobin Haemoglobin F – seen in developing foetes Haemoglobin A – seen in adults. Haemoglobin A has two identical alpha chains and beta chains . 34

35. The sickle-cell disease occurs when the 6th amino acid, glutamic acid in the beta chain, is replaced by valine to change its structure and function. Single nucleotide is substituted on 11 th chromosome. GAG to GTG 35

36. Nonsense mutation The nucleotide is substituted resulting in the formation of a stop codon. These stop codons are certain sequences of the base chain that have the capability to stop amino acid chain production. When the substitution occurs it will terminate the sequence of amino acids and prevent the formation of the correct protein. 36

37. Silent mutation A nucleotide can be substituted that results in the formation of the same amino acid, and this situation can make the multiple codons code for the same amino acid. 37

38. Frameshift mutation Inserting or deleting one or more nucleotides. Changes the “reading frame” like changing a sentence. The resulting protein is usually non functional TYPES OF FRAME SHIFT MUTATIONS Deletions mutations :- These mutations are caused due to the loss or deletion of one or more nucleotides. Insertion mutations : These mutations are caused by the addition of one or more extra nucleotides in a DNA molecule at one or more places. 38

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41. References Gardner, E., Simmons, M., & Snustad , D. Principles of Genetics , New Delhi:Wiley India, 2010. Gupta P.K, Genetics. Rastogi publications, 2004-2005. S.Clancy , Genetic mutation . Nature Education, 2008. https://www.ndsu.edu/ https://www.vedantu.com/biology/point-mutation https://byjus.com/biology/mutation-genetic-change 41

42. THANK YOU 42