Mutations and Their Types Quiz

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Questions and Answers

What type of mutation primarily accounts for about 90% of human genome variation?

Copy number variations

Tandem repeats

Single nucleotide polymorphisms (SNPs) (correct)

Insertion mutations

Which of the following best describes the potential consequences of splice site mutations?

They may alter pre-mRNA splicing, leading to abnormal proteins. (correct)

They can enhance protein synthesis.

They exclusively induce tumor formation.

They result in increased gene expression.

How can polymorphisms influence disease susceptibility?

They only occur in protein-coding regions of the genome.

They are exclusive to cancer susceptibility.

They can increase susceptibility to diseases or remain harmless. (correct)

They always cause direct changes in phenotype.

What clinical application depends on the variable number of tandem repeats (VNTR)?

Establishing paternity Signup and view all the answers

Where do polymorphisms primarily occur in the genome?

In intergenic regions and introns Signup and view all the answers

What is a point mutation?

A permanent change involving a single base substitution. Signup and view all the answers

Which of the following describes a missense mutation?

It results in the substitution of one amino acid for another. Signup and view all the answers

Which mutation type is least likely to affect the amino acid sequence?

Silent mutation. Signup and view all the answers

What is the possible result of a point mutation in the regulatory region of a gene?

Altered gene expression. Signup and view all the answers

How can a transition mutation be defined?

When one purine replaces another purine or a pyrimidine replaces another pyrimidine. Signup and view all the answers

What is a consequence of a silent mutation?

It produces the same amino acid as before. Signup and view all the answers

What type of mutation can lead to genetic diseases?

Point mutations in coding regions. Signup and view all the answers

What might be the effect of a partially acceptable missense mutation?

It may cause a protein to retain some functionality. Signup and view all the answers

What type of mutation results from the change of Glutamic acid to Valine?

Missense mutation Signup and view all the answers

Which condition is associated with missense mutations in the HFE gene?

Hereditary hemochromatosis Signup and view all the answers

What is the result of a nonsense mutation?

The protein is shortened Signup and view all the answers

What does a frameshift mutation typically result from?

Insertion or deletion of nucleotides Signup and view all the answers

What is a clinical implication of mutations in the HFE gene?

Liver damage and diabetes Signup and view all the answers

What type of genetic disorder is caused by the expansion of the CAG codon?

Huntington disease Signup and view all the answers

Which of the following mutations allows a protein to still bind and release oxygen, albeit abnormally?

Missense mutation producing Hb S Signup and view all the answers

What is the outcome of a trinucleotide repeat expansion mutation?

Amplification of a codon leading to extra amino acids Signup and view all the answers

Study Notes

Mutations

Permanent changes in DNA sequence
Can be reflected in mRNA base sequence and protein amino acid sequence
Can cause genetic diseases

Types of Mutations

Point Mutation (Single-base substitution)
- Substitution of original base in gene with another
- Transition: Purine replaced by purine or pyrimidine replaced by pyrimidine (e.g., A >>> G or C >>> T)
- Transversion: Purine replaced by pyrimidine or vice versa (e.g., T >>> A, C >>> A, T >>> G, C >>> G)
- Can affect coding or regulatory regions of a gene
- Can alter gene expression if regulatory sequences are affected
- Can produce disease alleles within coding regions

Consequences of Point Mutation

Silent Mutation
- Changed base may code for the same amino acid
- No effect on protein structure
- Usually occurs in the 3rd codon position (Wobble’s theory)
Missense Mutation
- Changed base may code for a different amino acid
- Can have variable effects on protein structure
- Acceptable Missense: May result in normal functional protein (e.g., hemoglobin β-chain)
- Partially Acceptable Missense: May produce a protein with altered function (e.g., Hb S)
- Unacceptable Missense: May produce a non-functional protein (e.g., Hb M)
Nonsense Mutation
- Changed base creates a termination codon
- Results in premature termination of translation
- Produces a shortened (truncated) protein

Hereditary Hemochromatosis (HH)

Common genetic disease
Caused by missense mutations in the HFE gene (Human homeostatic iron regulator protein)
Mutations used to screen at-risk populations
Results in iron overload, leading to liver damage, diabetes, skin pigmentation, and heart failure

Frame Shift Mutation

Deletion or insertion of one or more nucleotides in DNA
Alters mRNA reading frame
Produces different amino acids
Can have significant impact on protein structure

Trinucleotide Repeat Expansion

Amplification of a three-base sequence repeated in tandem
Causes extra copies of one amino acid in the protein
Example: Huntington disease (expansion of CAG codon in Huntington protein gene)
Results in an abnormally long protein, leading to toxic fragments and neuronal aggregation
Fragile X syndrome (expansion of CGG codon)

Splice Site Mutations

Mutations at splice sites alter intron removal from pre-mRNA
Produce abnormal proteins
Can lead to gene silencing and lack of protein production

Polymorphisms

Genotype changes that may or may not result in phenotypic changes
Phenotypic changes can be harmless, increase susceptibility to disease, or cause disease
Defined as sequence variation at a locus in >1% of a population
Primarily occur in non-coding regions (introns and intergenic regions)

Types of Polymorphisms

Single-base changes:
- Single nucleotide polymorphisms (SNPs)
- Account for 90% of human genome variation
Tandem Repeats:
- Variable number of tandem repeats (VNTRs)
- Short sequences of DNA repeated in tandem
- Number of repeats varies between individuals
- Serve as a molecular "fingerprint"

Clinical Implications of Polymorphisms

Paternity testing: VNTRs used in fingerprinting
Disease susceptibility: Can increase susceptibility to diseases like cancer and cardiovascular diseases
Disease screening: Used to screen high-risk individuals

Summary

Mutations are permanent changes in DNA sequence that can lead to altered proteins and genetic diseases. Different types of mutations, including point mutations, frame shift mutations, trinucleotide repeat expansions, and splice site mutations, can have a range of effects on protein structure and function. Polymorphisms, common variations in DNA sequence, can be harmless, increase disease susceptibility, or cause disease.

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Description

Test your knowledge on mutations, including point mutations and their consequences. This quiz covers various types of mutations, how they affect DNA and protein sequences, and their potential to cause genetic diseases. Make sure to review the concepts of silent and missense mutations.