Genetics Overview: Mutations and Abnormalities
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Questions and Answers

What genetic condition is characterized as an autosomal recessive trait that dilutes color expression?

  • Cystic fibrosis
  • Color blindness
  • Sickle cell anemia
  • Dilute color mutation (correct)

    • What would be the resulting phenotype for an organism with the genotype 'D-'?

  • No color phenotype
  • Diluted color phenotype
  • Normal color phenotype (correct)
  • Incompletely expressed color phenotype

    • Which of the following describes a mutation that could lead to a frameshift in coding regions?

  • Synonymous mutation
  • Single base substitution
  • Splice site mutation
  • Indel (insertion or deletion) (correct)

    • What is the characteristic outcome of a splice site mutation?

    <p>Altered mRNA splicing patterns</p> Signup and view all the answers

    In relation to muscular dystrophy in Golden Retrievers, what does a splice site mutation in intron 6 lead to?

    <p>Deletion of exon 7 from mRNA</p> Signup and view all the answers

    What type of genetic alteration results in aneuploidy?

    <p>Addition or loss of chromosomes</p> Signup and view all the answers

    Which of the following is NOT a result of defective chromosomal recombination?

    <p>Loss of muscle fibers</p> Signup and view all the answers

    What replaces thymine (T) in the mRNA structure?

    <p>Uridine (U)</p> Signup and view all the answers

    What is the main effect of somatic mutations during embryonic development?

    <p>They lead to the formation of mutant tissues.</p> Signup and view all the answers

    Which step occurs first in the PCR process?

    <p>Denaturation of the DNA.</p> Signup and view all the answers

    What method is primarily used to visualize DNA in agarose gel electrophoresis?

    <p>Ethidium bromide or SYBR Safe dye.</p> Signup and view all the answers

    What does the CT value represent in real-time quantitative PCR?

    <p>The cycle number at which fluorescence crosses a threshold.</p> Signup and view all the answers

    What distinguishes germ-line mutations from somatic mutations?

    <p>Somatic mutations can propagate through daughter cells.</p> Signup and view all the answers

    What is the role of Taq DNA polymerase during PCR?

    <p>To add nucleotides to the growing DNA strand.</p> Signup and view all the answers

    Which of the following processes is essential for detecting multiple nucleotide substitutions?

    <p>DNA sequencing.</p> Signup and view all the answers

    During which phase of PCR does the temperature drop to allow oligos to bind?

    <p>Annealing phase.</p> Signup and view all the answers

    What is the definition of aneuploidy?

    <p>Having fewer or more than the normal diploid number of chromosomes</p> Signup and view all the answers

    What are the consequences of polyploidy in mammals?

    <p>It is typically lethal at the embryonic or fetal stage</p> Signup and view all the answers

    What indicates a balanced translocation in an individual?

    <p>The person has a normal phenotype and full chromosome complement</p> Signup and view all the answers

    How does a reciprocal translocation affect fertility?

    <p>It can create unbalanced zygotes upon fertilization</p> Signup and view all the answers

    What are balanced changes in chromosome structure characterized by?

    <p>No change in overall DNA content of the cell</p> Signup and view all the answers

    Which of the following best describes monosomy?

    <p>Having lost one of a pair of chromosomes</p> Signup and view all the answers

    What is often the result of aneuploidy in autosomes?

    <p>Developmental problems, often lethal to the embryo</p> Signup and view all the answers

    What can occur during meiosis as a result of improper chromosome arrangements?

    <p>Genome rearrangements may lead to new functions</p> Signup and view all the answers

    What are disease susceptibility genes?

    <p>Genes with sequence variants associated with an increased risk of disease.</p> Signup and view all the answers

    What is the role of modifier genes?

    <p>They influence the phenotype resulting from mutations in other genes.</p> Signup and view all the answers

    What does an Odds Ratio (OR) greater than 1 indicate?

    <p>The condition is more likely in the first group than in the general population.</p> Signup and view all the answers

    What is a Quantitative Trait Locus (QTL)?

    <p>A chromosome region identified related to quantitative variation of traits.</p> Signup and view all the answers

    How do mutations differ from polymorphisms?

    <p>Mutations are detrimental heritable changes, while polymorphisms are common variations.</p> Signup and view all the answers

    Why is cancer considered a multi-gene disorder?

    <p>It arises from the accumulation of mutations in multiple genes.</p> Signup and view all the answers

    What does it mean when a QTL marker tests for only a proportion of genetic contribution to a trait?

    <p>It reflects only one out of many mutations contributing to that trait.</p> Signup and view all the answers

    What is commonly true of polymorphisms in a population?

    <p>They provide variability within a population.</p> Signup and view all the answers

    What type of mutation is mainly responsible for familial cancer?

    <p>Germ-line mutation</p> Signup and view all the answers

    Which of the following characteristics are shared by cancer cells that distinguish them from normal cells?

    <p>Defective response to DNA damage</p> Signup and view all the answers

    What is a primary role of mitochondria in cells?

    <p>Energy production</p> Signup and view all the answers

    How is mitochondrial DNA primarily inherited in mammals?

    <p>Uniparental maternal inheritance</p> Signup and view all the answers

    What causes the high mutation rate in mitochondrial DNA?

    <p>Reactive oxygen species</p> Signup and view all the answers

    What is a consequence of the low efficiency proofreading capacity of gamma DNA polymerase?

    <p>Higher likelihood of mutations</p> Signup and view all the answers

    Which term describes the process that produces energy within mitochondria?

    <p>Oxidative phosphorylation</p> Signup and view all the answers

    What is a significant feature of mitochondrial diseases?

    <p>Delays in onset with progressive decline</p> Signup and view all the answers

    Study Notes

    Dilute Colour Mutation

    • An autosomal recessive condition
    • dd results in a diluted colour
    • D- results in normal colour
    • CRICOS code 00025B

    Dosage Compensation and Tortoiseshell Cats

    • CRICOS code 00025B

    Mutations and Abnormalities

    • CRICOS code 00025B

    The Genetic Translation Code

    • Three nucleotides code for one amino acid (codon)
    • Start and stop codons signal the beginning and end of the amino acid chain
    • DNA genetic code uses adenine, thymine, cytosine, and guanine (ATCG)
    • In mRNA, thymine (T) is replaced with uracil (U)
    • CRICOS code 00025B

    Mutations

    • Changes in DNA or RNA
    • Single base substitution in coding regions can be silent (synonymous), missense (non-synonymous), or nonsense (stop)
    • Indel: insertion or deletion of one or a few nucleotides, can lead to frameshifts within coding regions
    • A splice site mutation alters nucleotides at splice control sequences changing the patterns of RNA splicing
    • CRICOS code 00025B

    Muscular Dystrophy in Golden Retrievers

    • A splice site mutation in intron 6 causes a complete deletion of exon 7 from mRNA
    • Leads to a frameshift in following exons
    • Loss of dystrophin from muscle
    • CRICOS code 00025B

    Defective Chromosomal Recombination/Segregation

    • Abnormalities can arise when chromosomes rearrange or fail to segregate properly
    • Numerical anomalies result in aneuploidy, either the addition or loss of individual chromosomes
    • Structural abnormalities are rearrangements of genetic material within or between chromosomes
    • Can be balanced or unbalanced
    • CRICOS code 00025B

    Sex Chromosome Aneuploidy

    • Female offspring can have the following:
      • XX
      • X0
      • XXX
    • CRIGOS code 00025B

    Loss or Gain of a Single Chromosome

    • Normal = euploidy = having the normal number of chromosomes
    • Abnormal = aneuploidy = having fewer or more than the normal diploid
    • Most common forms of aneuploidy are monosomy (loss of one of a pair of chromosomes) and trisomy (three chromosomes instead of a pair)
    • Effects of Aneuploidy of autosomes: Serious developmental problems, typically lethal = embryo/foetal loss i.e not passed on. Trisomies of small chromosomes can lead to live animals
    • Effects of polyploidy in mammals: In mammals, polyploidy is lethal, usually at embryonic/foetal stage, causes severe developmental abnormalities
    • CRICOS code 00025B

    Abnormal Chromosome Structure

    • Changes to the structure of chromosomes caused by mistakes in meiotic recombination and DNA break repairs
    • Balanced changes: do not change the overall DNA content of a cell, although the gene neighborhood is affected and might alter gene expression.
    • Unbalanced changes: overall loss or gain of total amount of DNA
    • CRICOS code 00025B

    Reduced Fertility due to Translocations

    • Complex arrangements of chromosomes during meiosis
    • Translocations can be inherited through balanced gametes
    • Translocations can lead to creation of balanced but unbalanced zygotes
    • Translocations can lead to reduced fertility
    • CRICOS code 00025B

    Reciprocal Translocation – Cause of Low Fertility

    • Individual has reciprocal translocation during meiosis
    • Balanced individual = has full complement of all chromosomal pieces
    • All gametes are functional, but some are unbalanced
    • Upon fertilization with normal gamete, some zygotes are unbalanced and die
    • Reduction in fecundity
    • Changes are inherited through two gametes with balanced translocation
    • CRICOS code 00025B

    Robertsonian Translocation

    • Same concept as Reciprocal Translocation
    • CRICOS code 00025B

    Abnormal Chromosome Structure

    • Genome rearrangement (inversion and translocation). Occurs during meiosis. Can lead to new functions or to lethal loss of function.
    • CRICOS code 00025B

    Mutation and Repair

    • CRICOS code 00025B

    Mutation Heritability Depends on Mutation Location

    • Somatic mutations:occur in non-reproductive cells passed onto daughter cells. Creates a clone of mutant cells - More widespread if occurring in embryo
    • Germ-line mutations: occur in cells that produce gametes passed to future generations. All cells in the offspring’s body carry the mutation
    • CRICOS code 00025B

    Genetic Tests

    • CRICOS code 00025B

    Sample Collection, DNA/RNA Extraction and Amplification

    • Avoid contamination and store/ship appropriately
    • DNA is stable, RNA is not
    • PCR (Polymerase Chain Reaction) is a technique used to amplify DNA segments
    • Real-time PCR can be used to quantify gene expression or DNA copy number
    • CRICOS code 00025B

    PCR Process

    • Three steps:

      • Denaturation: heating DNA to separate the strands
      • Annealing: primers bind to specific DNA sequences
      • Extension: Taq DNA polymerase adds dNTPs to create new complementary strands

    • Repeated cycles amplify the target DNA

    • CRICOS code 00025B

    Agarose Gel Electrophoresis

    • Used to separate DNA fragments based on size
    • Fluorescent dye that binds DNA eg ethidium bromide or SYBR Safe is added to the gel
    • DNA fragments are visualized under UV light
    • CRICOS code 00025B

    Real-Time Quantitative PCR (qPCR)

    • Measures DNA amplification in real-time
    • CT value = threshold cycle, a measure of the starting amount of DNA
    • Used for presence/absence (Syber or probes) or quantitative
    • CRICOS code 00025B

    DNA Sequencing

    • “Gold standard” for detecting single or multiple nucleotide substitutions
    • Provides detailed information about nucleotide changes
    • CRICOS code 00025B

    Gene Types in Multifactorial Disease

    • Disease susceptibility genes: gene sequence variants associated with an increased risk of disease but may not cause the disease on their own
    • Modifier genes: genes whose expression or function can influence the phenotype resulting from mutation of another independent gene
    • Mutations: Heritable detrimental sequence changes in a gene that are commonly associated with disease
    • Polymorphisms: Sequence variation (point mutation) among individuals that are common in a population (>1%) and that are usually not associated with disease
    • CRICOS code 00025B

    Testing for Multifactorial Diseases/Traits

    • If all the contributing genes, their interactions and environmental effects are known … then genetic testing could be undertaken as we do for Mendelian traits. But, we usually don’t know all, or even all the major, contributing genes, causative or associated gene variants
    • Therefore we measure risk of associated variants … Can use Odds Ratios
    • OR>1 indicates that the condition or event is more likely in the first group than the general population
    • OR<1 indicates that the condition or event is less likely in the first group than the general population
    • The closer the OR is to 1, the smaller the difference in effect between the two groups
    • CRICOS code 00025B

    Quantitative Trait Loci (QTLs)

    • Same principles from multi-factorial disease
    • Use the term QTL when identified chromosome region but not actual ‘causative’ mutation
    • A QTL can be represented by the actual mutation if it is known (direct test) or SNP/microsatellite marker (indirect test)
    • Each QTL marker tests only for a proportion of the genetic contribution to that trait.
    • CRICOS code 00025B

    Cancer Genetics

    • CRICOS code 00025B

    Cancer is a Multi-Gene Disorder

    • Cancer arises from the accumulation of mutations in multiple genes
    • A single mutation in a single gene is not sufficient to cause cancer
    • Familial cancer: germ-line mutation
    • Sporadic cancer: somatic mutation
    • CRICOS code 00025B

    Cancer Cell Characteristics

    • Defective response to DNA damage
    • Defective telomeres
    • Uncontrolled cell proliferation
    • Immortalization
    • Defective apoptosis
    • Induction of angiogenesis
    • Increased cell motility
    • Reduced cell adhesion

    Mitochondrial Disease

    • CRICOS code 00025B

    Mitochondrial DNA

    • Replicates separately from nuclear DNA
    • Codes for metabolic proteins (ATP synthesis, fatty acid metabolism, citric acid cycle)
    • Many essential genes for mitochondrial replication and function have been transferred to the nucleus
    • Nuclear genes are “protected” from mutagenic environment of mitochondria
    • CRICOS code 00025B

    Human mtDNA Map

    • 12S & 16S rRNAs
    • Cytochrome b
    • D-loop
    • tRNAs
    • Overlap of ATPase 6 and 8
    • CRICOS code 00025B

    Maternal Inheritance of Mitochondrial DNA

    • Uniparental (maternal) inheritance of mitochondria and hence mtDNA
    • Both sons and daughters inherit the mtDNA of their mother
    • Mitochondrial inheritance is thus “non-Mendelian” (ie not derived from both parents)
    • CRICOS code 00025B

    Nuclear-Encoded Mitochondrial Genes

    • Many essential genes for mitochondrial replication and function have been transferred to the nucleus
    • Nuclear genes are “protected” from mutagenic environment of mitochondria
    • Nuclear-encoded mitochondrial proteins synthesized in cytoplasm and imported into mitochondria facilitated by a signal peptide (SP)

    High Mutation Rate in mtDNA

    • Reactive oxygen species (ROS or free radicals) produced during oxidative phosphorylation
    • Low efficiency proof reading capacity of the gamma DNA polymerase
    • CRICOS code 00025B

    Mitochondrial Disease

    • Disease pathogenesis relates to oxidative phosphorylation … the process that produces energy
    • Mitochondrial diseases show delayed onset and progressive decline
    • CRICOS code 00025B

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    Description

    This quiz covers essential topics in genetics including dilute color mutation, dosage compensation in tortoiseshell cats, and the genetic translation code. Explore the mechanisms of mutations, their impacts, and how DNA and RNA variations lead to different conditions. Perfect for students in genetics courses.

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