Podcast
Questions and Answers
Which of the following is MOST likely to result in a frameshift mutation?
Which of the following is MOST likely to result in a frameshift mutation?
- Substitution of one purine base for another.
- Insertion of a single nucleotide in the coding sequence. (correct)
- Deletion of three consecutive nucleotides in the coding sequence.
- A point mutation in the third base of a codon.
A researcher is studying a gene in yeast and discovers a mutation that prevents the protein from being translated. Which type of mutation is MOST likely responsible?
A researcher is studying a gene in yeast and discovers a mutation that prevents the protein from being translated. Which type of mutation is MOST likely responsible?
- A nonsense mutation near the start codon. (correct)
- A missense mutation near the 3' end of the gene.
- A silent mutation in the middle of the gene.
- A point mutation in the intron.
A genetic test identifies a mutation in a non-coding region of a gene that results in significantly reduced levels of gene expression. Which of the following is the MOST probable mechanism?
A genetic test identifies a mutation in a non-coding region of a gene that results in significantly reduced levels of gene expression. Which of the following is the MOST probable mechanism?
- The mutation disrupts a promoter sequence. (correct)
- The mutation affects the mRNA stability.
- The mutation introduces a frameshift.
- The mutation creates a new splice site.
During DNA replication, a mismatched base pair is incorporated. If this error is NOT corrected by the proofreading mechanisms, which of the following outcomes is MOST likely?
During DNA replication, a mismatched base pair is incorporated. If this error is NOT corrected by the proofreading mechanisms, which of the following outcomes is MOST likely?
A scientist is studying a bacterial population and observes that some cells have developed resistance to an antibiotic. Which of the following mechanisms is MOST likely to be responsible for this observation?
A scientist is studying a bacterial population and observes that some cells have developed resistance to an antibiotic. Which of the following mechanisms is MOST likely to be responsible for this observation?
Which chromosome staining technique is most suitable for identifying regions of heterochromatin?
Which chromosome staining technique is most suitable for identifying regions of heterochromatin?
A male patient is diagnosed with Klinefelter syndrome. Which of the following karyotypes is most likely?
A male patient is diagnosed with Klinefelter syndrome. Which of the following karyotypes is most likely?
Which of the following chromosomal abnormalities involves the transfer of a segment of one chromosome to another non-homologous chromosome?
Which of the following chromosomal abnormalities involves the transfer of a segment of one chromosome to another non-homologous chromosome?
A child is diagnosed with Patau syndrome. Which karyotype is associated with this condition?
A child is diagnosed with Patau syndrome. Which karyotype is associated with this condition?
In Fluorescence In Situ Hybridization (FISH), what is the primary purpose of the DNA probe?
In Fluorescence In Situ Hybridization (FISH), what is the primary purpose of the DNA probe?
Which step in the FISH procedure directly follows the hybridization of the probe to the target DNA?
Which step in the FISH procedure directly follows the hybridization of the probe to the target DNA?
For which of the following applications is FISH least useful, according to the provided text?
For which of the following applications is FISH least useful, according to the provided text?
A researcher aims to determine if a bone marrow transplant was successful and of the correct sex. Which FISH application is most appropriate?
A researcher aims to determine if a bone marrow transplant was successful and of the correct sex. Which FISH application is most appropriate?
Which of the following best describes the direct impact of an intercalating agent like proflavine on DNA?
Which of the following best describes the direct impact of an intercalating agent like proflavine on DNA?
A mutation in a gene results in a protein with a significantly altered 3D structure and loss of function. Which type of point mutation is LEAST likely to cause this outcome?
A mutation in a gene results in a protein with a significantly altered 3D structure and loss of function. Which type of point mutation is LEAST likely to cause this outcome?
A researcher is studying a new viral strain and observes that it has a significantly higher mutation rate when exposed to UV radiation. Which DNA repair mechanism is MOST likely deficient in this viral strain?
A researcher is studying a new viral strain and observes that it has a significantly higher mutation rate when exposed to UV radiation. Which DNA repair mechanism is MOST likely deficient in this viral strain?
A scientist observes a mutation in a somatic cell of a multicellular organism. What is the MOST likely consequence of this mutation?
A scientist observes a mutation in a somatic cell of a multicellular organism. What is the MOST likely consequence of this mutation?
What is the consequence of a frameshift mutation in a protein-coding gene?
What is the consequence of a frameshift mutation in a protein-coding gene?
Which of the following mutations would be classified as a transversion?
Which of the following mutations would be classified as a transversion?
A geneticist is analyzing a new mutation that arose spontaneously in a bacterial population. What can be inferred about the cause of this mutation?
A geneticist is analyzing a new mutation that arose spontaneously in a bacterial population. What can be inferred about the cause of this mutation?
A patient is diagnosed with a genetic disorder caused by a chromosomal translocation. Which of the following best describes the underlying genetic change?
A patient is diagnosed with a genetic disorder caused by a chromosomal translocation. Which of the following best describes the underlying genetic change?
Why are mutations considered the 'raw material of evolution'?
Why are mutations considered the 'raw material of evolution'?
A researcher uses Giemsa G-banding on a metaphase chromosome spread. What specific chromosomal feature is being analyzed using this technique?
A researcher uses Giemsa G-banding on a metaphase chromosome spread. What specific chromosomal feature is being analyzed using this technique?
Flashcards
What are mutations?
What are mutations?
Alterations in the DNA sequence that can occur spontaneously or be induced by mutagens.
How do mutations arise?
How do mutations arise?
Can occur randomly during DNA replication or due to environmental factors.
What is a mutagen?
What is a mutagen?
A substance or agent that can cause mutations in DNA.
Effects of mutations?
Effects of mutations?
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What is DNA repair?
What is DNA repair?
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Quinacrine Q-banding
Quinacrine Q-banding
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Reverse R-banding
Reverse R-banding
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Centromere C-banding
Centromere C-banding
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Trisomy 21
Trisomy 21
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Turner Syndrome
Turner Syndrome
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Klinefelter Syndrome
Klinefelter Syndrome
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FISH (Fluorescence in situ hybridization)
FISH (Fluorescence in situ hybridization)
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Steps in FISH
Steps in FISH
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Mutation
Mutation
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Spontaneous Mutations
Spontaneous Mutations
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Induced Mutations
Induced Mutations
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Somatic Mutation
Somatic Mutation
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Gametic Mutation
Gametic Mutation
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Substitution Mutation
Substitution Mutation
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Transition
Transition
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Transversion
Transversion
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Silent Mutation
Silent Mutation
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Missense Mutation
Missense Mutation
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Study Notes
- Mutations are heritable changes in the nucleotide sequence of a given DNA.
- Mutations involve substitution, deletion, or insertion of one or more nucleotides.
- Mutations can affect the phenotype.
- Mutations are the major basis of diversity among organisms.
- Mutations are the raw material of evolution.
- Mutations are mostly caused by mutagens; for example: base analogs like 5-bromouracil (5-BU) and 2-amino-purine; alkylating agents like ethylmethane sulfonate (EMS); intercalating agents like proflavine, acridine orange, and ethidium bromide, etc.
- Mutations are caused by DNA damage from UV radiation, ionizing radiation (e.g., gamma rays and X-rays), and byproducts like reactive oxygen species, superoxides, and hydroxyl radicals.
- The body can repair mutations in normal conditions through base excision repair, nucleotide excision repair, and mismatch repair systems.
Classifications of Mutations
- Spontaneous mutations arise in the absence of known mutagens.
- Induced mutations occur due to the presence of mutagens or environmental agents.
- Somatic mutations originate in mitosis and affect a subset of cells.
- Gametic mutations originate in meiosis and affect all cells of an individual; they can be autosomal or X-linked.
Molecular Basis of Mutation
- Substitution involves a change in the sense of information (missense).
- A transition is a purine to purine or pyrimidine to pyrimidine change.
- A transversion is a purine to pyrimidine or vice versa change.
- A frameshift occurs by deletion or insertion of one base.
Base Substitution or Point Mutation
- A base substitution or point mutation is shown with a change in the codon sequence from GTT TTA GAT CCG TAC to ATT TTA GAT CCG TAC, which changes the amino acid from valine to isoleucine.
Silent Mutation
- A silent mutation changes one codon for an amino acid into another codon for that same amino acid.
- An example of a silent mutation is when the codon sequence ATC TTA GAT CCG TAC changes to ATC TTG GAT CCG TAC.
Missense Mutation
- A missense mutation is when the codon for one amino acid is replaced by a codon for another amino acid.
- Synonymous missense is when a codon specifies a chemically similar amino acid and does not alter protein function in many cases, exemplified by AAA changing to AGA.
- Nonsynonymous missense is when a codon specifies a chemically dissimilar amino acid, exemplified by UUU changing to UCU.
- Phenylalanine (F) is non-polar and hydrophobic, while Serine (S) is polar and hydrophilic.
- Point mutations and multiple variants in the "a determinant" region can destroy the antigenicity and immunogenicity of HBV.
Nonsense Mutation
- A nonsense mutation is when the codon for one amino acid is replaced by a translation termination codon.
Insertion Mutation
- An insertion mutation involves the addition of one or more nucleotide base pairs into a DNA sequence.
Deletion Mutation
- A deletion mutation involves the loss or removal of one or more nucleotide base pairs from a DNA sequence.
Frameshift Mutation
- Frameshift mutations result from one DNA base results in abnormal amino acid sequence.
Translocation
- Translocation occurs when a region from one chromosome is aberrantly attached to another chromosome, e.g., t(8;14) and t(9;22).
- Chronic myelogenous leukemia accounts for 20% of all leukemia cases characterized by an overproduction of granulocytic and monocytic series cells.
- The Philadelphia chromosome is present in >90% of patients with chronic myelogenous leukemia.
- Karyotype of chronic myelogenous leukemia: 46,XX,t(9;22)(q34;q11).
Chromosomes
- The diagram of a chromosome shows the short arm (p), centromere, long arm (q), kinetochore, sisters chromatids, and telomeres.
- Chromosomes can be metacentric, sub-metacentric, acrocentric, or telocentric relating to the position of the centromere.
Routine Chromosomal Analysis
- A routine chromosomal analysis includes short-term lymphocyte culture, lymphocyte harvest, slide preparation and staining, and slide analysis.
- Short-term lymphocyte culture uses standard media composed of RPMI 1640, fetal bovine serum, and penicillin-streptomycin along with the addition of phytohemagglutinin for 72-hour culture.
- Lymphocyte harvest involves the addition of colcemid (prevent spindle fiber formation), centrifugation, hypotonic solution (disrupts cytoplasmic material), and fixation
- Slide preparation and staining involve 24-hour slide aging.
- GTG-Banding technique is used with G-bands by Trypsin using Giemsa.
Slide Analysis
- The analysis is based on the International System of Human Cytogenetic Nomenclature (ISCN).
- Chromosomes are arranged according to size and banding pattern, and analyzed using Cytovision™ by Applied Imaging Inc. or Ikaros™ by Metasystems Inc.
- There are both Numerical Abnormalities and Structural Abnormalities (change in structure and morphology, and deviation from normal chromosome number -46.
Chromosomal analysis
- Types Include: Giemsa G-banding, Quinacrine Q-banding, Reverse R-banding, and Centromere C-banding.
- Giemsa G-banding: Treat metaphase spread with trypsin that digests part of chromosomal protein, stain with Giemsa and observe under light microscope
- Quinacrine Q-banding: Fluorescent staining method that uses quinacrine to identify chromosomes and their structural anomalies
- Reverse R-banding: Involves denaturing in hot acidic saline followed by Giemsa Staining
- Centromere C-banding: Used in identifying heterochromatin by denaturing chromosomes in a saturated alkaline solution
Chromosomal Aberrations
- Trisomy 21 (47, + 21)
- Trisomy 18 (47, + 18)
- Trisomy 13 (47, + 13)
- Turner syndrome (45, X)
- Klinefelter syndrome (47, XXY)
- Deletion, Duplication, Translocation, and Inversion
Genetic Syndromes
- Trisomy 21: Down Syndrome (47, + 21)
- Trisomy 18: Edward Syndrome (47, + 18)
- Trisomy 13 - Patau Syndrome (47, + 13)
- Turner Syndrome: Low birth weight, Swelling of hands and feet and Skin fold at the back of neck, etc
- Klinefelter Syndrome: Increased breast size, constant hand tremors, smaller penis and testes etc
Fluorescence in situ hybridization (FISH)
- This is a laboratory technique for detecting and locating a specific DNA sequence on a chromosome.
- The technique involves exposing chromosomes to a small DNA sequence ("probe") with a fluorescent molecule attached.
- The probe sequence binds to its corresponding sequence on the chromosome.
- FISH is useful in disorders with very small aberrations or samples with no metaphase cells available.
- Its steps include: Denaturation of the sample, Hybridization of probe to target cells, Washing, and Detection (fluorescent microscopy)
- Some applications: Detection of BCR-ABL, AML-ETO, PML-RARα, Y-Chromosome.
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