Genetic Mutations and Their Types

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Questions and Answers

What is the mutation rate of microsatellites per locus per gamete?

$1 imes 10^{-9}$

$1 imes 10^{-6}$

$1 imes 10^{-12}$

$1 imes 10^{-3}$ (correct)

What technique is used to rapidly isolate and amplify DNA fragments?

Polymerase chain reaction (PCR) (correct)

Sanger sequencing

Restriction digest

Gel electrophoresis

Which process is primarily responsible for separating DNA fragments according to size?

DNA replication

Hybridization

Polymerase chain reaction

Gel electrophoresis (correct)

What does the presence of SNPs indicate regarding their mutation rates?

They are identified at an average of 5 million instances. Signup and view all the answers

What small genomic changes arise from unequal crossing over?

Small deletions and duplications Signup and view all the answers

What type of damage do X-rays cause to DNA?

They break the DNA backbone. Signup and view all the answers

What is the role of DNA polymerase during replication?

To excise mismatched bases. Signup and view all the answers

Which class of DNA polymorphism arises from single base-pair substitutions?

Single nucleotide polymorphism (SNP). Signup and view all the answers

Which mechanism can increase mutation rates?

Mutagens. Signup and view all the answers

What is a polymorphic locus useful for in genetic studies?

Mapping studies and disease diagnosis. Signup and view all the answers

What describes the error rate of DNA replication?

Less than once in 109 base pairs. Signup and view all the answers

What do transposable elements do within the genome?

Move around and evade repair mechanisms. Signup and view all the answers

What defines a biallelic polymorphism?

Only two alleles exist at a locus. Signup and view all the answers

What type of mutation occurs when a purine is replaced by a pyrimidine?

Transversion Signup and view all the answers

Which of the following mutations results in the loss of one or more DNA pairs?

Deletion Signup and view all the answers

What describes a mutation where a block of one or more DNA pairs is added?

Insertion Signup and view all the answers

Which type of mutation involves a 180-degree rotation of a segment of DNA?

Inversion Signup and view all the answers

What characterizes a substitution mutation?

Replacement of one base with another Signup and view all the answers

Which of the following mutations might affect multiple genes at once?

Chromosomal rearrangements Signup and view all the answers

What mutation involves the exchange of parts between nonhomologous chromosomes?

Reciprocal translocation Signup and view all the answers

Which type of mutation is specifically characterized as a 'purine for purine' change?

Transition Signup and view all the answers

What is an example of a spontaneous mutation?

Natural genetic variation Signup and view all the answers

What type of mutation could potentially create a new gene function?

Insertion Signup and view all the answers

Which mutation type maintains the original sequence but changes the order of bases?

Inversion Signup and view all the answers

Which condition describes a substitution mutation where one base is replaced evenly?

Transition Signup and view all the answers

What factor has the least influence on spontaneous mutations?

Controlled laboratory conditions Signup and view all the answers

What is the primary characteristic of induced mutations?

They result from environmental factors Signup and view all the answers

Study Notes

Mutations: Primary Subject and Tool of Genetic Analysis

Mutations are heritable changes in base sequences, altering the information content of DNA.
Natural genetic variations exist.
Induced mutations can occur.
- Random mutagens occur without target.
- Specific target mutagens target a specific location.

Types of Mutations

Substitution: A base is replaced by another.
- Transition: Purine replaces purine or pyrimidine replaces pyrimidine.
- Transversion: Purine replaces pyrimidine or vice versa.
Deletion: One or more DNA pairs are lost.
Insertion: One or more DNA pairs are added.
Inversion: A 180° rotation of a DNA segment.
Reciprocal translocation: Nonhomologous chromosome segments swap places.
Chromosomal rearrangements: Alterations affecting multiple genes simultaneously.

Spontaneous Mutations

Spontaneous mutations occur at a very low rate.
Mutation rates from wild type to recessive alleles for coat color genes in mice display different frequencies.

Natural Processes Affecting DNA

Depurination: Hydrolysis of a purine base (A or G) occurs approximately 1000 times per hour per cell. This creates an apurinic site.
Deamination: Removal of an amino group from a base. This can change cytosine to uracil, potentially leading to a substitution to an A-T base pair after replication.

Other Factors Affecting DNA

X-rays: X-rays break the DNA backbone.
UV light: UV light produces thymine dimers.
Oxidation: Oxidation from free radicals, formed by irradiation, damages individual bases.

Mistakes during Replication

Errors during replication are rare (less than once in 10⁹ base pairs).
Proofreading enzymes correct errors. DNA polymerase possesses a 3'→5' exonuclease activity that checks for mismatches and removes them.

Unequal Crossing Over

Unequal crossing over creates one homologous chromosome with a duplication and the other chromosome with a deletion.

Transposable Elements

Transposable elements (TEs) move around the genome without being subject to excision or mismatch repair.
Two mechanisms of movement exist:
- Copy-and-paste; or
- Cut-and-paste.

Mutagens Increasing Mutation Rate

Base analogs: Have similar structures to normal bases, potentially being incorporated during replication, resulting in incorrect base pairings.
- 5-Bromouracil: A base analog that can mimic thymine or guanine.
Hydroxylating agents: Add a hydroxyl group to a base, causing a chemical change that might disrupt pairing.
- Hydroxylamine: A hydroxylating agent that converts cytosine to N-4-hydroxycytosine, which makes it pair with adenine instead of guanine.
Alkylating agents: Add ethyl or methyl groups to a base.
- Ethylmethane sulfonate: An alkylating agent changes guanine to 0-6-ethylguanine, altering its pairing.
Deaminating agents: Remove an amino group from a base.
- Nitrous acid: Removes an amino group from cytosine to uracil, changing the pairing capacity.

Intercalating Agents

Intercalating agents insert between bases.
- Proflavin is an intercalating agent causing insertion or deletion of a base pair in DNA.

Repair Enzymes

Repair enzymes fix errors created by mutations.
- Excision repair: Enzymes excise damaged regions of DNA and DNA polymerase and ligase repair the strand.

Direct Detection of Genotype

Distinguishes individual genomes.

Variation in Genomes

Members of the same species exhibit significant sequence variations in their genomes.
- High variation in base pairing and many polymorphic loci.
Polymorphism: Two or more alleles at a locus (location in the genome).
Alleles: Variations in the genome at a particular location.
DNA markers: Useful for mapping studies and disease diagnosis.
Anonymous loci: Locations in the genome with unknown functions.

Four Classes of DNA Polymorphisms

SNP (Single Nucleotide Polymorphism): Single base-pair substitutions (most common).
Microsatellites: Repeated units (2 to 5 base pairs).
Minisatellites: Larger repeats (1 to 20 kilobases)
Small changes in DNA: Deletions and insertions.

Polymerase Chain Reaction (PCR)

Used to rapidly isolate and amplify DNA fragments.
Employs oligonucleotide primers to copy DNA similar to DNA replication.
Cycles allow for exponential accumulation of target DNA.

Microsatellite Allele Detection Analysis

Analysis focuses on the size differences of microsatellite alleles using PCR and gel electrophoresis.

Gel Electrophoresis

Gel electrophoresis separates DNA fragments based on size.
Used to visualize amplified DNA fragments. Fragments are stained with dye for visualization.

Deletions, Duplications, and Insertions

Expand or contract the length of non-repetitive DNA.
Caused by unequal crossing over. Can also be caused by transposable elements.

Restriction Enzymes

Break down complex genomes into smaller fragments for study.
Fragment at specific sites on the genome.
Widely used restriction enzymes are listed.

SNP Detection by PCR

Requires sequence present on either side of the polymorphism for amplification from PCR primers.
Restriction enzymes are used to confirm the fragment presence.
Gel electrophoresis is then used for fragment visualization and identification.

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Description

This quiz explores the various types of mutations, including substitutions, deletions, insertions, and inversions. It also describes natural variations and induced mutations that impact genetic analysis. Test your understanding of how these changes affect DNA and heredity.