1. Genetic Mutations SDK Nov 2, 2012

2. OBJECTIVES By the end of this session the student should be able to:
Define Mutation
Frequency of mutations in normal individuals
Classify different types of mutation
Explain the mechanism of mutation
Explain the role of mutation in biodiversity
Explain how mutations can cause severe diseases
Give examples of deletions, duplications, and insertions in genes
Define trinucleotide repeat expansions and how they cause neurological diseases
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3. Mutation & Mutant
Replacement or change of a nucleotide base with another, in one or both strands, or addition or deletion of a base pair in a DNA molecule is called mutataion.
Mutations are changes in genetic material(Nitrogenous bases) – changes in DNA code(geneotype) and a mutant is the corresponding expression(Phenotype).
In gene mutations, the DNA code will have a base (or more) missing, added, or exchanged in a codon.
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4. How common are mutations?
Mutations occurs at a frequency of about 1 in every 1 billion base pairs
Everybody has about 6 mutations in each cell in their body!
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5. When everyone has mutations, Why they are not always seen
They are not always seen because the mutation may have occurred in a section of DNA that doesn’t make a protein.
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6. Mutations Outcome The affected gene may still function.
Mutations may be harmful.
Mutations may be beneficial.
Mutations may have no effect on the organism.
Mutations are a major source of genetic variation in a population increasing biodiversity.
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7. Mutations a cause of Biodiversity
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8. Does all mutations passed on to next generation?NO
Only mutations in gametes (egg & sperm) are passed onto offspring(Germ line Mutation) and this take place in Meiosis.
Mutations in somatic cells (body cells) only affect the body in which they occur and are not passed onto offspring and this take place in Mitosis.
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9. TRUE Brain Work 1 A mutation may happen in any gene. TRUE OR FALSE?
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10. Spontaneous and Induced Mutations
Spontaneous: Occur spontaneously without obvious reason.
Induced mutations: caused by mutagens.
Mutagens are the agent that causes the DNA code to change (mutate)
X-Ray
Chemicals
UV light
Radiation etc
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11. DNA Repair Mechanism
Our genes are subject to a countless of attacks by both environmental agents and endogenous processes that result in mutation.
DNA must maintain its integrity over lifetime.
There rae Five types of DNA repair systems :
One-step repair
Nucleotide excision repair (NER)
Base excision repair
Mismatch repair and
Recombinational repair
Defects in most of these pathways result in a predisposition to cancer.
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12. UV Light (Sun Light) Brain Work 2
Which of the following may cause mutations?
Coffee
UV light (sun light)
Hair gel
Vaccines
UV Light (Sun Light)
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13. Original The fat cat ate the wee rat.
Types of Mutations
Point mutations. A point mutation is a simple change in one base of the gene sequence.
2. Frame shift mutations. one or more bases are inserted or deleted
Original The fat cat ate the wee rat.
Point Mutation The fat cat ate the wet rat.
Original The fat cat ate the wee rat
Frame Shift The fat caa tet hew eer at
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14. Morphological Types of Point mutations
Transitions. Transitions occur when a
Purine is converted to a purine (A to G or G to A)
Pyrimide is converted to a pyrimidine (T to C or C to T)
2. Transversion. A transversion results when
Purine is converted to a pyrimidine (A to C or G to T)
Pyrimidine is converted to a purine. (T to A or C to G)
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15. Types of Mutations according to their effects on the protein (or mRNA).
Silent Mutations. Mutation in a codons that produce same amino acid. These mutations affect the DNA but not the protein. Therefore they have no effect on the organism’s phenotype.
CUU CUC
Missense Mutations. Missense mutations substitute one amino acid for another. Example. HbS, Sickle Cell Hemoglobin, is a change in the beta-globin gene, where a GAG codon is converted to GUG GAG GUG
Nonsense mutations. Mutation in a codons convert an amino acid into a stop codon. The effect is to shorten the resulting protein. Sometimes this has only a little effect, however, often nonsense mutations result in completely non-functional proteins.
UUU UAA\ UGA
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17. Frame-shift
In a frameshift mutation one or more bases are inserted, or deleted.
Because our cells read our DNA in three letter words, adding or removing one letter changes each subsequent word.
This type of mutation can make the DNA sequence meaningless .
For example:
Original= THE FAT CAT ATE THE WEE RAT
FRAMESHIFT= THE FAT CAA TET HEW EER AT.
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18. Brain Work 3
Mutations are a natural part of the cellular process reproduction. The cell has tools that catch and repair 99.9% of mutations.
TRUE OR FALSE?
TRUE
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19. TRUE Brain Work 4 Most mutations are caught and repaired in the cell.
TRUE or FALSE?
TRUE
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20. Classical Types of Point mutation Mutations
Point mutation occurs when the base sequence of a codon is changed. (ex. GCA is changed to GAA)
There are 3 types:
Substitution
Deletion
Also called frameshift mutations
Insertion
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21. Substitution
A substitution is a mutation that exchanges one base for another (i.e. a change in a single “chemical letter” such as switching an A to G.
For example:
CTGGAG
CTGGGG
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22. Substitution Mutations
Normal DNA: CGA – TGC – ATC
Alanine – Threonine - stop
Mutated DNA: CGA – TGC – TTC
Alanine – Threonine - Lysine
This is a substitution mutation
What will happen to the amino acids?
What has happened to the DNA?
The adenine was replaced with thymine
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23. The cat ate the rat
The hat ate the rat
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24. Clinical Examples
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25. Sickle Cell Anemia
Sickle cell anemia is the result of a (substitution) point mutation in codon 6 of the -globin gene resulting in the substitution of amino acid glutamic acid by valine
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26. Sickle Cell Anemia Under conditions of low oxygen tension, such as
Following exercise or
In an atmosphere containing a low oxygen level,
The following changes occur:
The haemoglobin agglutinates to form insoluble rod-shaped polymers
Red blood cells become distorted and sickle-shaped
The sickle-shaped cells rupture easily causing haemolytic anaemia
The sickle shaped cells tend to block capillaries interfering with the blood flow to various organs.
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27.  Thalassaemia
Substitution of C by U in mRNA that is coding  globin chain of 146 amino acid.
Resulted in the formation of a stop signal UAG in place CAG of glutamate in codon number 39.
This result in a shortened globin chain containing only 39 instead of the normal 146 amino acids in the -globin protein chain.
This protein is functionally useless and is equivalent to absence of -globin gives clinical symptoms of  thalassaemia,
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28.  Thalassaemia
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29.  Thalassemias
Beta thalassaemia is a genetic disorder in which there is lack of beta globin.
It may be the result of:
Deletion of the whole gene so that beta globin cannot not produced (designated  o )
Deletion of the promoter region so that transcription cannot occur (designated  o )
Deletion of a large part of the gene resulting in a grossly abnormal or reduced synthesis functional protein (designated  + )
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30. Clinical Features of  -Thalassaemia
Haemoglobin A (α2  2) cannot be produced
Hb F (α2 g2) is produced even in adults
Hb A2 (α 2 d2) formation is increased
Eerythrocytes are microcytic (small) due to lack of normal haemoglobin
Erythrocytes rupture easily causing severe haemolytic anaemia, requiring repeated blood transfusions
The bone marrow expands trying to compensate by increasing haemopoiesis.
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31. Clinical Features of  -Thalassaemia
The bones of the face and skull are thickened causing a characteristic facial appearance
The spleen and liver enlarge because haemopoietic tissue forms in them
Excess iron accumulates in the blood and is deposited in the heart, liver, pancreas and other organs (this is because of repeated transfusions while no blood is actually lost from the body)
Children have delayed growth and development and are prone to repeated infections
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32. Point Mutation In alpha-Globin Gene “Elongated α Globin Chain, Haemoglobin Constant spring \Wayne Hb”
Here the stop codon UAA at position 142 in the alpha (-) globin gene was substituted by the codon for glutamine.
Translation of the protein thus continued until a stop codon was encountered at codon 173.
The -globin was considerably elongated, resulting in a variant of haemoglobin termed Haemoglobin Constant spring\ Wayne Hb.
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33. Elongated α Globin Chain Or Haemoglobin Wayne
Hemoglobin Constant Spring. Hemoglobin Constant Spring is a variant in which a mutation in the alpha globin gene produces an alpha globin chain that is abnormally long. The quantity of hemoglobin in the cells is low for two reasons. First, the messenger RNA for hemoglobin Constant Spring is unstable. Some is degraded prior to protein synthesis. Second, the Constant Spring alpha chain protein is itself unstable. The result is a thalassemic phenotype. (The designation Constant Spring derives from the isolation of the hemoglobin variant in a family of ethnic Chinese background from the Constant Spring district of Jamaica.)
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34. CTGGAG CTGGCCTAG Insertion
Insertions are mutations in which extra base pairs are inserted into a new place in the DNA.
CTGGAG
CTGGCCTAG
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35. Insertion Mutations What will happen to the amino acids?
Normal DNA: CGA – TGC – ATC
Alanine – Threonine – stop
Mutated DNA: CGA – TAG – CAT – C
Alanine – Isoleucine – Valine
An adenine was inserted thereby pushing all the other bases over a frame.
This is an insertion mutation, also a type of frameshift mutation.
What has happened to the DNA?
What will happen to the amino acids?
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36. Insertion Mutations
The cat ate the rat
The cca tat eth era t
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37. Haemophilia A
An X-linked recessive disorder in which blood clotting does not occur due to deficiency of clotting factor VIII.
In most cases the mutation is the result of insertion of a large segment, consisting of about 3800 bp, in the coding region of the factor VIII.
This results in total inactivation of the protein.
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38. Haemophilia A
Inherited as a sex linked recessive trait with bleeding manifestations only in males.
Genes which control factor VIII and IX production are located on the x chromosome
Affected male marries a normal female: none of sons will be affected, all daughters will be carriers
Female carrier marries normal male: 50% chance sons will be affected and 50% chance daughters will be carriers
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39. Deletion
Deletions involve removal of one or more base pairs.
They vary greatly in size from deletion of a single base to deletion of a whole gene.
The clinical effects often depend on the size and location of the deleted part of the gene.
CTGGAG CT AG
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40. Deletion Mutations What has happened to the DNA?
Normal DNA: CGA – TGC – ATC
Alanine – Threonine – stop
Mutated DNA: CGA – TCA- TC
Alanine – Serine
What has happened to the DNA?
A guanine was deleted, thereby pushing all the bases down a frame.
What will happen to the amino acids?
This is called a deletion mutation, also a type of frameshift mutation.
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41. Muscular Dystrophy Deletions of Dystrophin Gene
Dystrophin is a protein that is an important component of skeletal muscle.
The dystrophin gene is located on the p arm of the X chromosome (Xp21.2).
It is a very large gene spanning 2.5 million bp of genomic DNA and consists of 79 exons coding for a protein of approximately 3600 amino acids (11kb).
The gene for dystrophin production sits on the X chromosome. If a normal gene for dystrophin is present, then the protein will be made. If the gene is missing or altered, dystrophin may not be produced at all or only in abnormal forms, resulting in Duchenne muscular dystrophy
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44. Muscular Dystrophy Deletions of Dystrophin Gene
Deletion of the whole or most of the dystrophin gene
Dystrophin may not be produced at all
Or produce in in abnormal forms,
Resulting in Duchenne muscular dystrophy
This is a severe X-linked recessive disorder that affects boys and is transmitted by carrier females. X linked Recessive disorder.
In affected boys there is almost complete lack of dystrophin, muscle weakness beginning in childhood and increasing progressively in severity so that the individual is wheel-chair bound at the age of about 15 years.
Death usually ensues in the early twenties due to respiratory muscle involvement.
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45. X linked Recessive disorder
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46. Becker Muscular Dystrophy(BMD)
Deletions involving a small non-critical part of the gene result in altered dystrophin.
This causes the clinical condition of Becker muscular dystrophy
in BMD muscle weakness begins in adolescence and is very slowly progressive, and affected individuals may lead an almost normal life.
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47. Deletion of one codon causing Cystic Fibrosis.
Cystic fibrosis is caused by a mutation in the Cystic Fibrosis Trans-membrane Regulator (CFTR) gene, that is located on chromosome 7.
This gene Produces a trans-membrane protein that regulates the flow of chloride ions into the cells.
The most common mutation is termed the ∆508 mutation, which is a deletion of a single codon at position number 508 in exon 10 of the CFTR gene.
Homozygotes for a ∆508 mutation have cystic fibrosis disease.
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48. Cystic Fibrosis.
CF is characterized by the secretion of very thick, mucus causing
Obstruction of the bronchi and predisposing to pulmonary infections,
Pancreatic duct obstruction,
Intestinal and liver problems and excess salt loss in sweat.
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49. The codons 92 to 97 of the -globin gene are deleted.
Deletion of 6 codons in the -globin gene resulting in a variant Hemoglobin
The codons 92 to 97 of the -globin gene are deleted.
This results in a shortened -globin protein that produces a haemoglobin variant termed Haemoglobin Gun Hill.
In homozygotes it produces mild clinical; symptoms.
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50. Codon no Codon Amino acid 91 CUG Leucine 92 CAC Histidine 93 UGU
Cysteine 94
GAC
Aspartic acid 95
AAG
Lysine 96 97
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51. Frame shift mutations
Frame shift mutations involve a deletion or insertion of one or two base pairs within a coding sequence of a gene.
As the coding message is read in triplets codons and deletions will altered the the reading frame of mRNA
This results in a non-sense sequence of amino acids till stop codon.
Original= THE FAT CAT ATE THE WEE RAT
Frame-shift= THE FAT CAA TET HEW EER AT
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52. Frame Shift Mutations(Deletion)
An example occurs in the -globin gene in which one nucleotide of codon 39 is deleted leads to altered sequence.
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53. Frame Shift Mutations(Insertion)
Insertion of a sequence of bases into a coding sequence of a gene.
Sometimes a whole gene sequence may be duplicated.
Hereditary motor and sensory neuropathy type I
A DNA segment at locus 17p11 is duplicated.
Tay-Sachs Disease
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54. Tay-Sachs Disease Tay-sachs disease is an autosomal recessive disorder
This genetic defect is located in the HEXA (hexosaminidase) gene, which is found on chromosome 15.
The hexa gene makes part of an enzyme called beta-hexosaminidase A
This enzyme helps break down a fatty substance called GM2 ganglioside in nerve cells.
Mutations in the HEXA gene disrupt the activity of beta-hexosaminidase A, preventing the breakdown of the fatty substances.
As a result, the fatty substances accumulate to deadly levels in the brain and spinal cord.
The buildup of GM2 ganglioside causes progressive damage to the nerve cells.
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55. Tay-Sachs Disease
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56. Tay-Sachs Disease
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57. Tay-Sachs Disease
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58. Tay-Sachs Disease S\S Loss of hearing Physical and mental retardation
Seizures
Dementia
And most noticeably detected by the red dots it causes on the retina of an individuals eye
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59. Trinucleotide Repeat Expansions
Trinucleotides are triplets of nucleotides that are repeated
The number of repeats varies in different individuals.
Trinucleotide repeats is CAG CAG CAG CAG CAG
Trinucleotide repeats are widespread in the genome, and may occur in exons, introns, promoter sequences or non-coding regions.
They are perfectly normal and occur in all individuals
However a mutation arises when the repeats become unstable and undergo expansion, namely an increase in the number of repeats as they are transmitted from one generation to the next.
When the number of repeats exceeds a certain limit, clinical symptoms occur.
An example is the huntingtin gene, which, when mutated, causes Huntington's disease.
Normal range of (CAG)n is 11 to 34,
Huntington's disease appear in individuals in whom the number of repeats is greater than 37.
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60. Huntington's Disease Autosomal Dominant Inheritance
Due to an excess of C-A-G nucleotide repeats(>37) in the IT15 gene on the short arm of chromosome 4 forms Huntington's protein.
Huntington's protein has increase number of glutamine (polyglutamine).
Excess of repeats causes the protein to form aggregates that are deposited within the neurons causing neuronal degeneration
Affects brain and spinal cord, especially the basal ganglia.
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61. Trinucleotide Repeat Expansions
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62. Clinical Manifestations
Most commonly appear in mid-forties
If appear at a younger age, more severe
Manifestations occur because of wasting away of brain cells.
Sudden jerky, involuntary movements throughout body
Difficulties with balance and coordination
Dysphasia
Hesitant/slurred speech
Progressive dysfunction of intellectual and thought processes (dementia)
Cognitive deficits
a. Working memory loss
b. Reduced capacity to plan, organize, and sequence
7. Restlessness, irritability
8. Depression or Euphoria
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63. What happens to a person who has a mutation?
Most of the time the mutation is harmless because 95% sections of DNA do not code for protein (junk DNA).
But sometimes the mutations can cause disorders such as Huntington’s disease and sickle cell anemia etc.
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64. Flyaway Mutation Brain Work 5
Which of these is NOT a type of mutation.
a) Point mutation
b) Flyaway mutation
c) Frameshift mutation
d) Nonsense mutation
Flyaway Mutation
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65. Brain Work 6 The correct answer is B deletion.
1. THE CAT SAW THE FAT RAT
2. THE CAT SAW THE RAT
The change in Statement 1 to form Statement 2 is most similar to what type of mutation?
Insertion
Deletion
Substitution
Frameshift
The correct answer is B deletion.
Because the sentence is missing the word fat which occurs in deletion as it is the removal of a section of DNA.
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66. Brain Work 7 5′AGAUCGAGU3′ → 5’ACAUCGAGU3′
The chain above represents three codons Which of the following changes would be expected in the amino acid chain if the mutation shown above occurred?
The amino acid sequence would be shorter than expected.
The identity of one amino acid would change.
The amino acid sequence would remain unchanged.
The identities of more than one amino acid would change.
The correct answer is B because according to the codon chart if G is switched by a C then one amino acid is affected because now instead of coding for Arginine it now codes for Threonine.
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67. Thank You
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