PREPARE BY: Miss lock shu ping
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Transcript of PREPARE BY: Miss lock shu ping
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PREPARE BY: MISS LOCK SHU PING
CHAPTER 7.0: MUTATION
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Mutation
MUTATION CLASSIFICATION
AND TYPES
GENE MUTATION
CHROMOSOMAL MUTATION
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1.Explain mutation2.Classify mutation into ‘gene
mutation’ and ‘chromosomal mutation’.
3.State the types of mutation4.Define mutagen5.State types of mutagen
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MUTATION ?
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A permanent change in the amount, arrangement or structure of the DNA of an organism which can passed down to the next generation.
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WHAT IS MUTATION?
‘Changes in the genetic material (genes or
chromosomes) of a cell’Can be inherited if mutation occurs in reproductive cells during formation of
gametes
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Types of mutation
- mutations that cause by mutagen
- e.g: exposure to mutagen
- mistakes happen spontaneously during DNA replication, DNA repair, or DNA recombination.
- e.g: nondisjunction during meiosis
( details will be explain in 16.3)
Based on the cause
Spontaneous mutation Induced mutation
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Spontaneous Mutation
mistakes happen spontaneously during DNA replication, DNA repair, or DNA recombination.
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Induced Mutation
Mutations that cause by mutagen
A variety of agents increase the frequency of
mutation
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- Physical and chemical agents that induces changes in DNA
Physical agent:Ultraviolet rayIonizing radiation (X-ray, gamma ray, alpha particles, neutron and electron)
Chemical agent:Mustard gas, nitrous acid, base analogue etc.Colchicine , ethidium bromide
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Physical agentPhysical agent EffectIonizing radiation • -breaks in one or both
strands (can lead to rearrangements, deletions, chromosome loss, death if unrepaired; this is from stimulation of recombination)
• -damage to/loss of bases (mutations)
• -crosslinking of DNA to itself or proteins
UV radiation pyrimidine dimers in DNA
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Chemical agentChemical agent Effectnitrous acid- It causes C to U, meC to
T, and A to hypoxanthine deaminations.
ethyl methanesulfonate mutagenic and recombinogenic, or mispair to result in mutations upon DNA replication.
Colchicine Prevent the formation of spindle fibre
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Shortwave UV (UVA) Causes Thymidine Dimers
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Mutation that causes by agent orange .
About 500 000 children in Vietnam born with birth defects during Vietnam war
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Mutant • A mutated gene, alternatively,
• An organism carrying a gene that has undergone a mutation that
• shows new phenotype traits as a result from mutation
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New phenotypes traits showed by this children as a result of mutation
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GeneticMutation
1. Base substitution
2. Base insertions3. Base deletions4. Base inversion
Chromosomal Mutation
1. Structural change / Chromosome Aberration
2. Alterations of chromosome number
Aneuploidy Euploidy /
Polyploidy
Mutation classificationBy effect on structure
of gene (involve small scale mutation)
of chromosome (involve large scale mutation)
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Genetic Mutation
Chromosomal Mutation
Mutation
Base substitutionBase insertionsBase deletionsBase inversion
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1.Explain gene mutation2.Classified gene mutation3.Describe base substitution as point
mutation4.Explain frameshift mutation5.Descibe base insertion as a frameshift
mutation6.Describe base deletion as a frameshift
mutation
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16.2 Gene Mutation/ Point Mutation
• A type of mutation which involved• A change in the nucleotide sequence of the DNA
within a gene
change the amino acid sequence and thus, changes
the proteinDifferent protein produced as the effect of mutation may not function as normal
Example : sickle cell anemia
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change the amino acid sequence
changes the protein
Change the DNA nucleotide sequence
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AGCTTA
TCGAAT
AGCGTTA
TCGCAAT
AGCGTA
TCGCAT
AGCTA
TCGAT
AGTCTA
TCAGAT
Normal
DeletionSubstitutionInsertion Inversion
Gene Mutation
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Classification of gene mutation• Base substitution – one or a few base pairs in the
nucleotide sequences in genes is substitute (replaced)
• Base insertions – addition of 1 or a few base pairs in the nucleotide sequences in genes
• Base deletions – loss of 1 or a few base pairs in nucleotide sequences
• Base inversion – 2 base pairs or more are inverted in nucleotide sequence
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• Base Substitution :
• Base Insertion:
THE FAT CAT ATE THE RATTHE FAT CAR ATE THE RAT
THE FAT CAT ATE THE RATTHE FAT CAT CAT ETH ERA
• Base Deletion :
• Base Inversion :
THE FAT CAT ATE THE RATTHE ATC ATA TET HER AT
THE FAT CAT ATE THE RATTHE FAT CAT ATE THE TAR
Analogy that can be made to show point mutation
AGCGTA
TCGCAT
AGCTA
TCGAT
AGTCTA
TCAGAT
AGCGTTA
TCGCAAT
AGCTTA
TCGAAT
Normal DeletionSubstitutionInsertionInversion
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• one or a few base pairs in the nucleotide sequences in genes is replaced with another base pairs.
• Can cause changes in base sequence – results in changes of codon . E.g: (UAU change to UGU)
• 1 codon = 3 base/ nucleic acid (coding for 1 amino acid)
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CAC-AAG-UAU-CAC-UAA
his lys tyr his stop
CAC-AAG-UGU-CAC-UAA
his lys cys his stop
Before mutation
Substitution mutation
Point Mutationa type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA.
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Changes in codon:
Leads to amino acid changesThe altered codon codes for different amino acid
Changes a codon to stop codon (UAG / UAA / UGA ) Leading to a nonfunctional protein
Missense mutation nonsense mutation
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Changes in codon
Nonsense
Mutation changes a
codon to stop codon
Leading to a nonfunctional protein
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Changes in codon
Leads to amino acid changes
the altered codon codes for an amino acid that is not the right sense.
Missense
Mutations
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Changes in codonSilent
Mutations have no effect on
the encoded protein.
a change in a base pair transform one codon into another that translated into the same amino acid.
happens because of redundancy in the genetic code.
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AGU AGCSER SER
Silent Mutatio
ns
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Changes in codon:
Leads to amino acid changesThe altered codon codes for different amino acid
Changes a codon to stop codon (UAG / UAA / UGA ) Leading to a nonfunctional protein
Missense mutation nonsense mutation
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Base substitutionCAC-AAG-UAU-CAC-UAA his lys tyr his stop
CAC-AAG-UGU-CAC-UAA his lys cys his stop
CAC-AAG-UAG his lys stop
Before mutation
Missense mutation
Nonsense mutation
Differences between missense and nonsense mutation is missense mutation altered codon codes for different amino acid while nonsense mutation alteres codon to stop codon.
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EFFECT OF BASE SUBSTITUTION
Sickle cell Anemia
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SICKLE-CELL ANEMIA
Missense mutation
Defective red blood cell
Abnormal Hb – Sickle (S) shape
Hb ~ 4 polypeptide chain
(2- & 2-)
Encode by different gene
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HOW SICKLE-CELL ANEMIA HAPPEN?
Happens because substitution mutation
Amino acid valine replaces glutamic acid at a single position in the protein (-strand)
Patient suffer from anemia ~ Hb-S stiff & tend to accumulate in small capillary
Hb is not efficient of transporting
oxygen
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Missense mutation
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Sickle cell Anemia• abnormal haemoglobin crystallizes &
erythrocyte is pulled into a sickle shape• the cells fragment easily or clump
together to clog the capillaries (and less O2 is transported)
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TRY THIS…
A. GGCATT
B. GGCCATT
C. GGCTT
D. GCGCTT
State what type of gene mutation below:
Normal DNA : GGCCTT
GGCATT BASE SUBSTITUTION
GGCCATT BASE INSERTION
GGCTT BASE DELETION
GCGCTT BASE INVERSION
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WHAT ARE THE DIFFERENCES BETWEEN MISSENSE AND NONSENSE MUTATIO N?
Missense mutation
altered codon codes
for different amino acid
nonsense mutation
altered codon to
STOP codon.(UAG / UAA /
UGA )
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What is the genetic disorder shown above?
Sickle- cell anemia
What type of gene mutation that cause this genetic disorder to happen? Why?
Because of substitution mutation. Amino acid valine is replaced by glutamic acid at a
single position in the protein (-strand)
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Point Mutations in Coding Sequences
Missense – changes amino acid Nonsense – creates stop codon
Frameshift – alters remainder of reading frame results in completely different amino acid sequence.
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FRAME-SHIFT MUTATIONS
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• Involve insertion/deletion of a base pair or more into the nucleotides sequence of DNA
• Many of these deletions/insertion start in the middle of a codon
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• Shifting the reading frame by one or two bases • Frame shift mutations cause the gene to be
read in the WRONG three base groups (codon)
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Example
Insertion of U base
Change the sequence of amino acids
Deletion of C base
Resulting in stop codon-no further
amino acid produces
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• From the mutation point, it abrupts the coding sequence of amino acid. Changes in codons results in changes in amino acids
• All the nucleotides downstream of the deletion/ insertion will be improperly grouped into codons.
different polypeptide is produced.
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Frame-shift Mutations
• The result will be – extensive missense, ending sooner or – later in nonsense - premature termination.
• Effect ~ usually harmful to human• e.g: Major thalasemia (mutant
homozygote alleles)
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A C A C G C A C U C C C
Amino acid 1
Amino acid 2
Amino acid 3
Amino acid 4
Codon 1
Reading frame in mRNAFrame-shift Mutations
Normal
Mutant A C A C G C A C U C C C
Codon 2 Codon 3 Codon 4
Codon 1 Codon 2 Codon 3
Amino acid 1
Amino acid 2
Amino acid 3
Reading frame is shift one base infront
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FRAMESHIFT MUTATION
Nonsense
Non frameshift
Extensive missense
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• Additions of nucleotide pairs in a gene• All the nucleotides that downstream of the
insertion will improperly group into codons.• Analogy:THE FAT CAT ATE THE RATTHE FAT CAT CAT ETH ERA
insertion improperly group into codons
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Extensive missense
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• Losses of nucleotide pairs in a gene• All the nucleotides that downstream of the
deletion will improperly group into codons.• Analogy:
– THE FAT CAT ATE THE RAT– THE ATC ATA TET HER AT
improperly group into codons
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Extensive missense
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• Eg. of disorder due to base deletion is thalasemia– deletion of nucleotide base pairs for
genes which – control the production of Hb α and β
chains– major thalassemia causes serious
anaemia
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• 2 base pairs or more in nucleotide sequence are inverted
• Change the codons => changes in amino acid
• Usually the effect is minor phenotype abnormality
• Normal code: AGA-GTC-TTC ser glu lys
• Base inversion: AGA-TGC-TTC ser thr lys
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Base Substituti
on
Base Insertion
Base Deletion
Base Invertion
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Genetic Mutation
Chromosomal Mutation
Mutation
Chromosome aberration
Alterations in chromosome
number
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1.Explain chromosomal mutation
2.Classify chromosomal mutation into chromosomal aberration and chromosomal number alteration .
3.Explain chromosomal aberration
4.State and describe types of chromosomal aberration
Chromosomal Mutation
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Chromosomal MutationDefinition:
• Abnormalities ~ in chromosomal structure (chromosome aberration) & changes in chromosome number (aneuploidy / euploidy)
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Types of chromosome mutation
Chromosome aberration
Alterations in chromosome
number
Euploidy(Polyploidy)
Aneuploidy
DeletionInversion
Translocation
Duplication
Structural change
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Chromosome Aberration• Involving the breakage of chromosome
and rearrangement a certain segment or parts of chromosome
• 4 types : DeletionInversion
Translocation
Duplication
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DELETION
ChromosomalMutations:
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DELETION
DUPLICATION
ChromosomalMutations:
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DELETION
DUPLICATION
INVERSION
ChromosomalMutations:
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DELETION
DUPLICATION
INVERSION
TRANSLOCATION
ChromosomalMutations:
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the lost of 1 segment containing 1 or more genes
ABCDEFGHI
Break off
Break off
ABC
GHI
DE
F
ABCGHI
Losing middle section
Deletion
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Example: Cri-du-chat syndrome
1.due to deletion of a section of the short arm of chromosome 5
2.characteristics:• small head• unusual facial features• mentally retarded• cries like the mew of a cat
3. Usually dies in infancy/ early childhood
krē-du̇-ˈshä-
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Example: Cri-du-chat syndrome
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• small head• unusual facial features• mentally retarded• cries like the mew of a cat
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a region of a chromosome breaks off and rotates through 180° before rejoining the chromosome
ABCDEFGHI
break
off
break
off
ABCFEDGHI
ABC
GHI
DEF
Inversion
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Centromere lies within inverted
region
Centromere lies outside inverted
region
Inversion
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Inversion
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Involves a region of a chromosome breaking off and rejoining either the other end of the same chromosome or another non-homologous chromosome
Translocation
A B C D E F G H I chromosome 1
M N O P Q R S chromosome 2
A B P Q R S
F G H IC D EN OMreciprocal
translocation
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• Most common: RECIPROCAL TRANSLOCATION[ 2 non-homologous chromosomes exchange fragments ]
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• In non-reciprocal translocation, a chromosome transfers a fragment without receiving any in return
• Example: Robertsonian translocation
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• Robertsonian translocation involves breaks at the extremes ends of the short arms of two nonhomologous chromosomes (13,14,15, 21 and 22).
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a region of a chromosome becomes duplicated; an additional set of genes exists
ABCDEFGHI Additional
set of genes
ABCDEFGHIFGHI
Duplication
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Differences between chromosomal mutation and gene/point mutation
Chromosomal mutation Gene/point mutation
A process that cause changes in chromosome structure or number
A process that causes changes in the base sequence of the DNA
Types of chromosomal mutation are chromosomal aberration and alteration in chromosome number.
Types of gene mutation are base substitution, base inversion, base deletion and base insertion.
No frameshift mutation Base deletion and base insertion cause frameshift mutation
No production of non-functional protein
Leads to production of non-functional protein
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1. The DNA nucleotide base sequence can be altered in several ways.Which of the following is NOT involved in gene mutation?
A. SubstitutionB. InversionC.DeletionD.Translocation
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The figure below shows a pair of homologous chromosomes during prophase I.
What could have cause this?
A B C G H
A B C G H
D F
E
A.SubstitutionB.InversionC.DeletionD.Duplication
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The figure shows two types of chromosomal mutations to the genetic sequence below.
A B C D E F G H
A B E D C F G H A B E F G H
I II
What are the processes that cause the chromosomal mutation I and II above?
I IIA Inversion DeletionB Inversion DuplicationC Deletion InversionD Translocation Deletion
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Try this….Determine the types of mutation
shown in the figure below.Normal gene sequence ABCDE FGH(i) ABCE FGH(ii) ADCBE FGH(iii)ABCBCDE FGH(iv)ABCDE MNOPQ
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