Mutation Types and Mechanisms
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Questions and Answers

What are the two main categories of mutations based on their effect on offspring?

Somatic mutations and germ-line mutations

What are the two main categories of mutations based on their scale?

Chromosome mutations and gene mutations

What are the two types of base substitutions?

  • Transition (correct)
  • Deletion
  • Transversion (correct)
  • Insertion

What are the two types of indels?

<p>Deletion (A), Insertion (D)</p> Signup and view all the answers

What is an expanding nucleotide repeat?

<p>An insertion mutation where the number of copies of a set of nucleotides increases in succeeding generations.</p> Signup and view all the answers

What is the hairpin model and how does it relate to expanding nucleotide repeats?

<p>The hairpin model proposes that the number of copies of a trinucleotide can increase in replication due to the formation of hairpins, which can lead to expanding nucleotide repeats.</p> Signup and view all the answers

What is a forward mutation?

<p>A mutation that alters a wild-type phenotype.</p> Signup and view all the answers

What is a reverse mutation?

<p>A mutation that changes a mutant phenotype back into the wild type.</p> Signup and view all the answers

What is a silent mutation?

<p>A change in the nucleotide sequence of DNA that does not alter the amino acid sequence of a protein.</p> Signup and view all the answers

What is a loss-of-function mutation?

<p>A mutation that causes the complete or partial absence of normal function.</p> Signup and view all the answers

Loss-of-function mutations are usually dominant.

<p>False (B)</p> Signup and view all the answers

Gain-of-function mutations are usually recessive.

<p>False (B)</p> Signup and view all the answers

What is a conditional mutation?

<p>A mutation that is expressed only under certain conditions.</p> Signup and view all the answers

What is a lethal mutation?

<p>A mutation that causes premature death.</p> Signup and view all the answers

What is a suppressor mutation?

<p>A mutation that hides or suppresses the effect of another mutation at a distinct nucleotide site.</p> Signup and view all the answers

What are the two types of suppressor mutations?

<p>Intragenic (B), Intergenic (D)</p> Signup and view all the answers

What is an intragenic suppressor mutation?

<p>A suppressor mutation that occurs in the same gene as the mutation that it suppresses.</p> Signup and view all the answers

What are the four main causes of mutations?

<p>Radiation (A), Spontaneous chemical changes (D), Spontaneous replication errors (E), Chemically induced mutations (F)</p> Signup and view all the answers

What is a spontaneous replication error?

<p>A spontaneous mutation that arises from natural changes in DNA structure or from errors in replication.</p> Signup and view all the answers

What is an incorporated error?

<p>The incorporation of a damaged nucleotide or mismatched base pair into a DNA molecule.</p> Signup and view all the answers

What is a replicated error?

<p>An incorporated error that is replicated, leading to a permanent mutation.</p> Signup and view all the answers

What are two causes of deletions and insertions?

<p>Strand slippage and unequal crossing over</p> Signup and view all the answers

What is depurination?

<p>The break in the covalent bond connecting a purine base to the deoxyribose sugar, resulting in the loss of the purine base.</p> Signup and view all the answers

What is a chemically induced mutation?

<p>A mutation that is caused by an environmental agent that damages DNA.</p> Signup and view all the answers

What is a base analog?

<p>A chemical substance that has a structure similar to that of one of the four standard nitrogenous bases of DNA and can be incorporated into newly synthesized DNA molecules.</p> Signup and view all the answers

What is an alkylating agent?

<p>Alkylating agents can cause mutations by altering the pairing properties of bases.</p> Signup and view all the answers

What is hydroxylamine?

<p>A specific base-modifying mutagen that adds a hydroxyl group to cytosine.</p> Signup and view all the answers

What is an intercalating agent?

<p>A chemical that intercalates between adjacent bases in DNA, distorting the three-dimensional structure of the helix.</p> Signup and view all the answers

What is the effect of UV radiation on DNA?

<p>UV light can cause the formation of pyrimidine dimers, which are bulky lesions that distort the configuration of DNA and often block replication.</p> Signup and view all the answers

How do bacteria survive UV radiation?

<p>Bacteria can use the SOS system to replicate their DNA in the presence of DNA damage.</p> Signup and view all the answers

What is the Ames test?

<p>A simple test for evaluating the potential of chemicals to cause cancer.</p> Signup and view all the answers

What are transposable elements?

<p>DNA sequences capable of moving from one site to another within the genome.</p> Signup and view all the answers

What are the features of transposable elements?

<p>Transposable elements have flanking direct repeats and terminal inverted repeats.</p> Signup and view all the answers

How do transposable elements transpose?

<p>Transposable elements transpose by a process that involves staggered breaks in the target DNA, joining the transposable element to the single-stranded ends of the target DNA, and DNA replication at the single-strand gaps.</p> Signup and view all the answers

Transposable elements can transpose as both DNA and RNA.

<p>True (A)</p> Signup and view all the answers

What are retrotransposons?

<p>Type of transposable element in eukaryotic cells that transposes through an RNA intermediate using reverse transcriptase.</p> Signup and view all the answers

What are the two types of transposition for DNA transposons?

<p>Nonreplicative transposition (B), Replicative transposition (C)</p> Signup and view all the answers

What are the mutagenic effects of transposition?

<p>Transposable elements can cause mutations by inserting into genes and disrupting their function, promoting DNA rearrangement, and causing deletions, inversions, and duplications.</p> Signup and view all the answers

What causes color diversity in grapes?

<p>The mutagenic effects of transposition.</p> Signup and view all the answers

What are four common DNA repair systems?

<p>Mismatch repair, direct repair, base-excision repair, and nucleotide-excision repair.</p> Signup and view all the answers

DNA repair systems are specific to the type of damage they repair.

<p>False (B)</p> Signup and view all the answers

What is mismatch repair?

<p>The process that corrects mismatched nucleotides in DNA immediately after replication has been completed.</p> Signup and view all the answers

What is direct repair?

<p>DNA repair in which modified bases are changed back into their original structures.</p> Signup and view all the answers

What is base-excision repair?

<p>DNA repair that first excises modified bases and then replaces the entire nucleotide.</p> Signup and view all the answers

What is nucleotide-excision repair?

<p>DNA repair that removes bulky DNA lesions that distort the double helix.</p> Signup and view all the answers

What are the underlying causes of several genetic diseases?

<p>Defects in DNA repair.</p> Signup and view all the answers

Flashcards

Mutation

Inherited alterations in the DNA sequence.

Somatic Mutation

Mutations in non-reproductive cells.

Germ-line Mutation

Mutations in reproductive cells.

Chromosome Mutation

Large-scale changes in chromosome structure or number.

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Gene Mutation

Small DNA changes affecting a single gene.

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Base Substitution

One base is replaced by another.

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Transition

Purine replaces purine, or pyrimidine replaces pyrimidine.

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Transversion

Purine replaces pyrimidine, or vice-versa.

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Indels

Insertions or deletions of nucleotides.

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Insertion

Adding one or more nucleotides.

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Deletion

Removing one or more nucleotides.

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Expanding Nucleotide Repeats

Repeated nucleotides increase in number.

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Forward Mutation

Changes a wild-type phenotype.

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Reverse Mutation

Changes a mutant phenotype back to wild type.

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Silent Mutation

No change in the protein sequence despite DNA changes.

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Missense Mutation

Changes one amino acid.

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Neutral Mutation

Missense mutation with little or no effect on protein function.

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Nonsense Mutation

Changes a sense codon to a stop codon.

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Loss-of-Function Mutation

Reduces or eliminates a gene's function.

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Gain-of-Function Mutation

Creates a new protein function.

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Conditional Mutation

Mutation expressed only under certain conditions.

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Lethal Mutation

Mutation causing death.

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Study Notes

Mutation Types and Mechanisms

  • Mutations are inherited alterations in DNA sequences, a primary driver of genetic variation and evolution. They also contribute to many diseases.
  • Somatic mutations occur in non-reproductive cells and aren't passed to offspring.
  • Germ-line mutations are in reproductive cells, thus can be inherited. They affect all cells of the offspring.

Mutation Scales

  • Chromosome mutations involve large-scale changes in chromosome structure or number.
  • Gene mutations are smaller alterations affecting a single gene.

Gene Mutations: Molecular Nature

  • Base substitutions involve replacing one base with another.
    • Transitions are more common (purine for purine, or pyrimidine for pyrimidine).
    • Transversions involve switching a purine for a pyrimidine.
  • Indels (insertions/deletions) are among the most frequent types of gene mutation, often leading to frameshift mutations. Frameshift mutations alter downstream amino acid sequences or introduce premature stop codons.

Expanding Nucleotide Repeats

  • These are insertion mutations where the number of repeated nucleotide triplets (most often) increases across generations.
  • Common causes include issues with DNA replication machinery.
  • Repeat length relates to severity or age of onset and mutation probability
  • Effects occur in both coding and non-coding regions

Mutation Functional Effects

  • Forward mutations alter wild-type phenotypes.
  • Reverse mutations (reversions) revert mutant phenotypes to the wild type.
  • Silent mutations have no impact on protein sequence due to the redundant nature of the genetic code.
  • Missense mutations cause an amino acid change in the protein.
    • Neutral mutations are missense mutations with minimal functional impact.
  • Nonsense mutations introduce premature stop codons.
  • Loss-of-function mutations reduce or eliminate protein function(recessive).
  • Gain-of-function mutations create new/altered protein functions often in a dominant fashion.

Other Mutation Types

  • Conditional mutations are expressed only under certain conditions.
  • Lethal mutations cause premature death.
  • Suppressor mutations counteract other mutations at different sites.
    • Intragenic suppressors occur within the same gene. They can make compensatory changes in folding, alter reading frames, or alter the original mutation in the same codon, essentially reverting the initial amino acid sequence.
    • Intergenic suppressors are in different genes; they can influence mRNA translation.

Mutation Causes

  • Spontaneous Replication Errors:

    • Tautomeric shifts lead to non-standard base pairings during replication.
    • Wobble allows for non-canonical base pairings.

  • Spontaneous Chemical Changes:

    • Depurination (loss of a purine base).
    • Deamination (loss of an amino group).

  • Chemically induced mutations. Mutagens increase mutation rates beyond spontaneous levels.

  • Radiation. Ionizing and non-ionizing radiation can induce mutations.

Chemically Induced Mutations

  • Base analogs mimic normal bases and can cause mispairing.
  • Alkylating agents add alkyl groups to bases and disrupt base pairing.
  • Deamination agents convert bases to different forms (e.g., nitrous acid).
  • Hydroxylamine adds hydroxyl groups to specific bases, causing mispairing.
  • Intercalating agents cause DNA distortions, frequently leading to frameshifts.

Radiation Effects

  • UV radiation causes pyrimidine dimers, often blocking replication or leading to cell death. Bacteria have repair mechanisms for these, but can make errors.
  • SOS system in bacteria allows replication in the presence of damaged DNA but increases the mutation rate.

Detecting Mutagens

  • The Ames test screens for mutagenic chemicals, often carcinogens. It uses Salmonella auxotrophs for detecting reverse mutations, thus aiding hazard identification.

Transposable Elements

  • Transposable elements move within the genome, and are a common cause of mutations.
  • They constitute a substantial portion of many genomes (over 40% of the human genome).

DNA Repair Systems

  • Various systems repair DNA damage. Systems exist for different sizes and types of damage.
  • Mismatch repair corrects mismatched base pairs.
  • Direct repair restores original base structures—without removing the nucleotide, but fixing the base structure.
  • Base excision repair removes specific damaged bases, then replaces the whole nucleotide.
  • Nucleotide excision repair removes larger DNA lesions.

Defects in DNA Repair and Disease

  • Defects in DNA repair systems contribute to several genetic predispositions and diseases.

Grape Color Diversity

  • Transposition effects in grapes, including altered anthocyanin production, drive color differences.

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Description

Explore the world of mutations with this quiz focusing on their types and mechanisms. Understand the differences between somatic and germ-line mutations, as well as the scales at which mutations occur. Test your knowledge on base substitutions and indels.

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