mutation - dr. h.b. mahesha · frequency of total mutations - 10-7to 10-12 /organism (i.e.,...

MUTATION

Dr.H.B.Mahesha

Associate Professor and Head

Department of Sericulture

Yuvaraja’s College

University of Mysore, India.Sunday, December 30, 2018 www.hbmahesh.weebly.com 1

Significance of Mutations

Sunday, December 30, 2018 www.hbmahesh.weebly.com 2


Mutation is an abrupt qualitative or quantitative change in the genetic material/Any change in the nucleotide sequence of DNA, which gives rise to a mutant genotype

The organism which undergoes mutation is known as mutant

HistorySeth Wright, 1791


Mutation - Coined by Hugo de Vris in1900 to explain the heritable changes

in evening primrose Oenothera lamrckiana

Mutagenesis - Process of producing mutations

Mutagen - A physical/chemical/biological agent that causes mutations

T.H.MorganT.H. Morgan 1910 Drosophila melanogaster


ClassificationBased on the origin: Natural / Artificial (induced)

Based on the cells: Somatic/Gametic

Based on chromosomes: Autosomal / Allosomal

Based on direction: Forward/Reverse

Based on size: Point/Gross

Silent Mutations.

Leaky mutations.

Nonsense Mutations or

Chain termination Mutation etc.,


Natural MutationFrequency of total mutations - 10 -7 to 10 -12/organism

(i.e., 0.0000001- 0.000000000001)Frequency of detectable mutations – 1 in 10 6 (i.e., 0.000001)

Eg., Tautomerism:-The ability of a molecule to exist in more than one chemical form


Tautomerism


Induced MutationInduced artificially by exposing them

(organisms) to abnormal environment.


MutagensPhysical –Radiations: i. Ionizing-X-rays, gamma, Alpha,

Beeta, protons, nutrons etc.,

ii. Non Ionizing -UV

Temperature-

Chemical – Auerbach & Robson 1947

Base Analogues: 2,aminopurine, 5-bromourasil etc.,Base Analogues: 2,aminopurine, 5-bromourasil etc.,

Base Modifying agents: Nitrous acid, Hydroxylamine etc.,

Distortion producing agents: Proflavin, acridine orange etc.,


Biological Mutagens: H. Pylori

Hepatitis virus

H. papiloma virus


Point Mutation / Gene MutationA mutation that changes only one small area or one

nucleotide in a gene

Earliest record of point mutation dates back to

1791 by Seth Wright.

Since then mutations have been reported in E. Since then mutations have been reported in E.

coli, Neurospora, Pea, Maize, Rodents, Fowls,

Man, etc.,


Frame Shift MutationA mutation that inserts or deletes a single base

(normally single rarely more) will change the reading frame for the entire subsequent sequence.

A change of reading frame is called Frame shift mutation.mutation.


Frame Shift Mutation may be DeletionInsertion


Substitution:- 1. Transition 2. Transversion


Transversion


Chemical MutagenesisMorgan 1934 – Drosophila with Alcohol

Chemicals: Activity can not be guessed based on

structure

Types:

Copy Errors by Base AnaloguesCopy Errors by Base Analogues

Direct Effect on DNA

Agents Producing Distorsions in DNA


Copy Errors by Base Analogues

Eg.,


Thymine 5 Bromouracil

Direct Effect on DNAeg., Nitrous acid (HNO2), Hydroxylamine (NH2OH),Alkylating agents


Guanine �� Uracil =Adenine

Cytocin (NH2OH) �� Modified Base=Adenine

Alkylating Agents:

EMS, EES, DES, etc., are extensively used in genetic research.


Agents Producing Distortions in DNAEg., Acridine Orange & Proflavin


��


Intercalation resulting in addition of the base


Intercalation resulting in

deletion of the base


RADIATION MUTAGENESIS

Ionizing radiations:- High-energy radiation capable of producing ionization in substances through which it passes.

Ionization:- Any process that leads to the dissociation of a neutral atom, molecule or dissociation of a neutral atom, molecule or other species into ions; the state of being ionized.

Eg., X-rays, α, β, gamma rays, fast moving particles

etc.,

Non Ionizing radiations:- Uv, Radio waves,

Visible Light


Effect of radiation on DNA molecule


Thymine Dimers

T=T �� 50%


T=T �� 50%

T=C �� 40%

C=C�� 10%

Ionizing


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mutation - dr. h.b. mahesha · frequency of total mutations - 10-7to 10-12 /organism (i.e.,...

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