Mutation chapter

1. Presented by- SULAGNA MUKHERJEE
Course- M.Sc 1st Semester
Department- Biotechnology
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2.  Introduction
 General Characters
 Role of Mutation
 Types of Mutation
 Mutation Rate and Frequency
 Recent Developments in Mutation
 References
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3.  The term “MUTATION” was first coined by
scientist Hugo De Vries in 1901.
 A sudden change occurring in hereditary
materials(DNA and chromosomes).
 Most mutation are the result of error during DNA
replication process/error during DNA repair. Some
types of mutations are known to be caused by
certain chemicals and non ionizing radiation UV.
 The process by which mutation is produced is
called Mutagenesis.
 An organism exhibiting a novel phenotype as a
result of the presences of a mutation is referred to
as a Mutant.
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4.  Random events in terms of the time of their occurance and the gene in
which they occur.
 Mainly harmful but some can be beneficial or neutral.
 Recurrent, i,e., the same mutation may be expected to occur in
different individuals of a given generation or those belonging to
different generations.
 Can occur in any tissue or cell of an organism and mutational events
can occur during any developmental stage of organisms.
 Many agents, both physical and chemical, increase the frequency of
mutation by several fold, known as Mutagens.
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5.  Ultimate source of all genetic variation and it
provides the raw material for Evolution.
 Mutations results into the formation of alleles,
without mutation all genes would exist in only
one form.
 Organism would be able to evolve and adapt to
environmental change.
 Ultimate source of Variation.
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6. Types of
mutation
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7.  May Involve:
 Changing the structure of a
chromosome.
 The loss or gain of part of a
chromosome.
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8.  Five types exist:
 Deletion
 Inversion
 Translocation
 Non-disjunction
 Duplication
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9.  Due to breakage.
 A piece of a chromosome is lost.
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10.  Chromosome segment breaks off.
 Segment flips around backwards.
 Segment reattaches.
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11.  Involves two chromosomes that aren’t
homologous.
 Part of one chromosome is transferred to
another chromosomes.
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12.  Failure of chromosomes to separate during
meiosis.
 Causes gamete to have too many or too few
chromosomes.
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13.  Occurs when a gene sequence is
duplicated.
 Results in multiple copies of that
region.
 It results from an unequal crossing
over between chromosomes during
meiosis.
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16. Number of ways to classify gene
mutations:
 On the basis of the molecular nature of
the defect
 On the basis of tissue of origin
 On the nature of the phenotypic effect-
- amino acid sequence of the protein is
altered or not
 On the basis of the causative agent of
the mutation
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17. Mutations on the basis of the molecular
nature of the defect:
Point Mutations
 Base substitution
 Insertions & deletions
Base Substitution
• Simplest type of gene mutation
• Involves the alteration of a single
nucleotide in the DNA
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18. GGG AGT GTA GAT
CGT
CCC TCA CAT CTA GCA
CCC TCA CAT CTA GCA
GGG AGT GCA GAT
CGT
A base substitution
CCC TCA CGT CTA GCA
GGG AGT GCA GAT
CGT
GGG AGT GTA GAT
CGT
CCC TCA CAT CTA GCA
First cycle of DNA replication
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19. Base substitution is of two types:
 Transition:
Purine is replaced with a purine
A G
G A
Pyrimidine is replaced with a pyrimidine
T C
C T
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20.  Transversions:
A purine is replaced by a pyrimidine
A C
A T
G C
G T
or a pyrimidine is replaced by a purine
C G
C A
T G
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21. Insertions & Deletions
 2nd major class of gene mutation.
 Addition or the removal, respectively, of one or
more nucleotide pair.
 Usually changes the reading frame, altering all
amino acids encoded by codons following the
mutation.
 Leads to frame shift mutations.
 Addition or deletions in multiples of three
nucleotides will lead to addition or deletion of
one or more nucleotides.
 These mutations are called in-frame insertions
and deletions, respectively.
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22. (Leads to frame shift
mutation)
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23. Based on how a base-pair substitution is translated via
the genetic code, the mutations can be of the
following types:
 Missense mutation: a base is substituted that alters a
codon in the mRNA resulting in a different amino acid in
the protein product.
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24.  Nonsense mutation: changes a sense codon into a
nonsense codon. Nonsense mutation early in the mRNA
sequence produces a greatly shortened & usually
nonfunctional protein.
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25.  Neutral mutation: Mutation that alters the amino acid
sequence of the protein but does not change its function
as replaced amino acid is chemically similar or the affected
amino acid has little influence on protein function.
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26.  Silent mutation: Alters a codon but due to degeneracy of
the codon, same amino acid is specified.
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27.  Suppressor mutation:
• Suppresses the effect of other mutation.
• Occurs at a site different from the site of original
mutation.
• Organism with a suppressor mutation is a double
mutant but exhibits the phenotype of unmutated
wild type.
• Different from reverse mutation in which
mutated site is reverted back into the wild type
sequence.
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28. Mutations on the basis of tissue of origin:
 Somatic Mutation:
 Occurs in somatic cells.
 Passed on to other cells through the process of mitosis
 Germline mutation:
 They occur in the cells that produce gametes
▪ Passed on to future generations
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29. Mutations on the basis of phenotypic effects of
mutations:
 Most common phenotype in natural populations of the
organism is called as wild type phenotype.
 The effect of mutation is considered with reference to
wild type phenotype.
Forward mutation: A mutation that alters the wild
type phenotype to mutant type.
Reverse mutation (reversion): A mutation that
changes a mutant phenotype back in to the wild type.
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30. Mutations on the basis of causative agents
of Mutation:
 Spontaneous:
 Mutations that result from natural changes in
DNA.
 Induced:
 Results from changes caused by
environmental chemicals & radiations.
 Any environmental agent that increases the rate of
mutation above the spontaneous is called a
mutagen such as chemicals & radiations.
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31. Chemical Mutagens: First discovery of a chemical
mutagen was made by Charlotte Auerbach.
 Base Analogs:
 Chemicals with structures similar to that of any
of the four standard bases of DNA.
 DNA polymerases cannot distinguish these
analogs.
 They may be incorporated into newly
synthesized DNA molecules.
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32. Examples of base analogs:
o 5-Bromo uracil- Base analog of Thymine
o 2-amino purine- Base analog of Adenine
 Base Modifying agents:
 Modifies the chemical structure and properties of the
bases.
Examples of base modifying agents:
o Nitrous acid- Causes deamination
o Hydroxylamine- a hydroxylating agent
o Ethyl methyl sulfonate- Causes alkylation
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33.  Intercalating Agent:
 They produce mutations
by sandwiching
themselves (intercalating)
between adjacent bases in
DNA.
 They distort the three-
dimensional structure of
the helix and cause single-
nucleotide insertions and
deletions in replication.
 These insertions and
deletions frequently
produce frameshift
mutations.
 Proflavin, acridine orange,
ethidium bromide, and
dioxin are the examples of
intercalating agents.
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34. Physical Mutagens:
Mutations that are caused
physically involves physical
mutagens.
 UV light:
 Causes the formation of
abnormal chemical bonds
between adjacent
pyrimidine molecules in the
same strand of the DNA
double helices.
 Mainly forms thymine-
thymine dimers.
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35.  Ionizing Radiations:
 In 1927, Hermann Muller
demonstrated that mutations could
be induced by X-rays.
 X-rays, gamma rays, and cosmic rays
are all capable of penetrating tissues
and damaging DNA.
 They remove electrons from the
atoms that they encounter, changing
stable molecules into free radicals
and reactive ions which then alter the
structures of bases and break
phosphodiester bonds in DNA.
 Ionizing radiation also frequently
results in double-strand breaks in
DNA.
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36.  Mutation Rate:
 The frequency with which a gene changes from
the wild type to a mutant is referred to as the
mutation rate.
 Expressed as the number of mutations per
biological unit i.e. mutations per cell division, per
gamete per round of replication.
e.g. mutation rate for achondroplasia (hereditary
dwarfism) is about 4 mutations per 100,000
gametes.
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37.  Mutation Frequency:
 Incidence of a specific type of
mutation with in a group of
individual organism.
e.g. for achondroplasia, the mutation
frequency in united states is about
2x10⁻⁴.
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38. (1) New genetic mutations make swine flu
virulent- The H1N1 influenza(swine flu) is undergoing genetic
mutations, making it more virulent and resistant to conventional
treatment. The new viral morphology prevents the antibodies, which
were developed against the older strains, from recognising the new
strains and binding them against the virus. Earlier, studies had
detected possible D222G mutation in HA(hemagglutinin) gene of
Indian isolates of swine flu virus. According to a study by the
Massachusetts Institute of Technology, one of the new mutations is in
an amino acid form called D225 thats linked with increased disease
severity. Another mutation in the T200A position, allows
hemagglutinin to bind more strongly to glycan receptors, making the
virus more infectious.
-By J Umamaheshwara Rao, Deccan Chronicle. Jan 31, 2017, 7:38 am IST.
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39. (2) The Zika Virus grew deadlier with a small
mutation, study suggests- It remains one of the great
mysteries of the Zika epidemic. The Zika virus cause thousands
of babies to be born with microcephaly, unusually small and
damaged brains. It is prevailing mostly in Latin America. The
Mutation called S139N, first arose in an Asian strain of the Zika
virus in 2013, which is linked to an increase in babies born with
microcephaly. In a laboratory dish, the S139N strain killed more
human cells important to early brain development than an
earlier strain without the mutation. Further studies showed
that it just a single mutation that is taking place on a protein
involved in making the virus’s protective coating.
- By Pam Belluck and Donald G. McNeil Jr, The New York Times,
28 Sep, 2017.
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40. 1. iGENETICS- A molecular approach. Peter J. Russell. 3rd
Edition, Chapter 7- DNA mutation and DNA repair.
Pearson Benjamin Cummings Publishing. ISBN: 0-321-
56976-8 / 978-0-321-56976-9
2. https://en.m.wikipedia.org/wiki/Mutation/
3. http://www.slideshare.net/SHIKHAYASHVEER/typesof
mutation/
4. http://www.google.co.in/amp/www.deccanchronicle.co
m/amp/lifestyle/health-andwellbeing/310117/new-
genetic-mutation-make-swine-flu-virulent.html
5. http://nytimes.com/2017/09/28/health/zika-mutation-
microcephaly.html
6. https:// www.ncbi.nlm.nih.gov/m/pubmed/28971967/
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