Most biological molecules have a limited lifetime. Many proteins, lipids and RNAs are degraded when they are no longer needed or damaged, and smaller molecules such as sugars are metabolized to compounds to make or store energy. In contrast, DNA is the most stable biological molecule. The DNA is passed from one generation to another, and it is degraded only when cells die. However, it can change, i.e. it is mutable. Mutations, changes in the nucleotide sequence, can result from errors during DNA replication, from covalent changes in structure because of reaction with chemical or physical agents called mutagens.

1. Ripal Mistry
Assistant Professor, SPCP, Bakrol.

2. Introduction
 Most biological molecules have a limited lifetime. Many proteins, lipids
and RNAs are degraded when they are no longer needed or
damaged, and smaller molecules such as sugars are metabolized to
compounds to make or store energy.
 In contrast, DNA is the most stable biological molecule. The DNA is
passed from one generation to another, and it is degraded only when
cells die. However, it can change, i.e. it is mutable.
 Mutations, changes in the nucleotide sequence, can result from errors
during DNA replication, from covalent changes in structure because
of reaction with chemical or physical agents called mutagens
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3. Types of Mutations
 The mutation is a process that produces a gene or chromosome that
differs from the wild type (arbitrary standard for what “normal” is for an
organism).
 The mutation may result due to changes either on the gene or the
chromosome itself. Thus, broadly mutation maybe:
o Gene mutation where the allele of a gene changes.
o Chromosome mutation where segments of chromosomes, whole
chromosomes, or entire sets of chromosomes change.
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4. Types of Mutations
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5. Types of Mutations
A. Type of Cell involved
 Somatic mutations
 occur in a single body
cell and cannot be
inherited.
 Germline mutations
 occur in gametes and
can be passed onto
offspring.
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6. Types of Mutations
B. Mode of Origin
 Spontaneous mutations
 The spontaneous mutations occur suddenly in the nature and their
origin is unknown. They are also called “background mutation” and
have been reported in many organisms.
 Induced mutations
 Besides naturally occurring spontaneous mutations, the mutations
can be induced artificially in the living organisms by exposing them to
abnormal environment such as radiation, certain physical conditions
(i.e., temperature) and chemicals.
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7. Types of Mutations
C. Direction of Mutation
 Forward mutations
 In an organism when mutations create a change from wild type to
abnormal phenotype, then that type of mutations are known as
forward mutations. Most mutations are forward type.
 Reverse mutations
 The forward mutations are often corrected by error correcting
mechanism, so that an abnormal phenotype changes into wild type
phenotype.
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8. Types of Mutations
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9. Types of Mutations
D. Size and Quality
 Point mutation
 When heritable alterations occur in a very small segment of DNA
molecule, i.e., a single nucleotide or nucleotide pair, then this type of
mutations are called “point mutations”.
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10. Types of Mutations
o Transitions : In this case, a purine (or a pyrimidine) is replaced by
another.
o Transversions : These are characterized by replacement of a purine
by a pyrimidine or vice versa.
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11. Types of Mutations
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12. Types of Mutations
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13. Types of Mutations
 Frameshift Mutation
 These occur when one or more base pairs are inserted in or deleted
from the DNA, respectively causing insertion or deletion mutations.
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14. Types of Mutations
E. Physical agents:
 Radiation:
 Radiations are the first mutagenic agent reported in 1920. UV rays, X-
rays, alpha rays, neutrons, and other ionizing and non-ionizing
radiations are mutagenic.
 The electromagnetic radiation is also one of the known mutagens that
cause lethal or sub-lethal mutations (Kill the organism/cell or alter the
function of the cell or protein or a gene). The iodizing radiation
produces the free radicals that damages, not even the DNA but also
proteins and lipids present in a cell.
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15. Types of Mutations
 UV-rays:
 The UV-light is a non-ionizing type of radiation having less energy in
it, used in the sterilization and decontamination process during the
cell culture and microbiological experiments. The DNA and protein
absorb UV light of 260 and 280nm, respectively.
 UV-A: nearly visible range (320nm) causes pyrimidine dimers.
 UV-B: (290-320nm) emitted by the sunlight. These UV rays are highly
lethal to our DNA.
 UV-C: (180-290nm) one of the most energy-consuming forms of the
UV which is extremely lethal.
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16. Types of Mutations
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17. Types of Mutations
 Heat:
 Heat is another mutagen that provokes mutations in our DNA. when
we heat the DNA, over a certain degree (>95°C), the DNA becomes
denatured- two single-stranded DNA is generated from the dsDNA.
Also, extreme heat also damages DNA and breaks the
phosphodiester bonds too.
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18. Types of Mutations
F. Chemical mutagens:
 Base analogs:
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19. Types of Mutations
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20. Types of Mutations
 Alkylating agents:
 Ethylnitrosourea, mustard gas and vinyl chloride are common
alkylating agents that add alkyl group to the DNA and damages it. The
agents induce base-pairing errors by increasing ionization and
produces gaps in the DNA strand.
 Intercalating agents:
 Ethidium bromide used during the agarose gel electrophoresis is one
of the intercalating agents. Other intercalating agents like proflavine,
acridine orange, or daunorubicin operated by the same mechanism
alike the EtBr.
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21. Types of Mutations
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22. Types of Mutations
 Metal ions:
 Metal ions also dangerous to our DNA as it acts in varieties of
different ways. Nickel, chromium, cobalt, cadmium, arsenic, chromium
and iron are some of the common metal ions cause mutations.
 The metal ions work by producing ROS (reactive oxygen species),
hindering the DNA repair pathway, cause DNA hypermethylation or
may directly damages the DNA.
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23. Types of Mutations
G. Biological agents:
 Virus: Viruses insert their DNA into our genome and disrupt the
normal function of DNA or genes. Once it inserts DNA, the DNA is
replicated, transcribed and translate viral protein instead of our own
protein. Mature viral particle forms in a cell.
 Bacteria: Some bacteria are also dangerous for our DNA- cause
inflammation. It provokes DNA damage and DNA breakage.
 Transposons: Less known biological mutagens are transposons. The
transposons are non-coding DNA sequences, jumps from one place
to another place in a genome and influence the function of genes.
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