Genetics of Quantitative Traits
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Questions and Answers

What is currently the preferred method for delivering DNA into cells in gene therapy?

  • Particle bombardment
  • Direct injection
  • Electroporation
  • Viral vectors (correct)

    • Which vector is mentioned as having a common target for the immune system that can reduce transgene expression?

  • Lentivirus
  • Adenovirus (correct)
  • Herpes virus
  • Retrovirus

    • What is a benefit of ex vivo gene therapy?

  • It targets multiple tissues simultaneously.
  • It has no immune response issues.
  • It allows for random gene integration.
  • It removes cells for editing before reinjection. (correct)

    • What can be added to a transgene to help prevent inappropriate gene expression?

    <p>Insulators</p> Signup and view all the answers

    Which of the following is a potential risk associated with gene therapy involving adenovirus?

    <p>Lethal immune responses</p> Signup and view all the answers

    What type of diet is often recommended for treating OTC deficiency?

    <p>Low-protein diet</p> Signup and view all the answers

    Which technique is mentioned as being potentially harmful to cells during DNA transfer?

    <p>Electroporation</p> Signup and view all the answers

    What factor plays a crucial role in ensuring that the transgene is expressed at an adequate level?

    <p>Strong promoters</p> Signup and view all the answers

    What is the expected phenotypic effect of additive inheritance?

    <p>A phenotypic effect of 0, 1, or 2</p> Signup and view all the answers

    Which hypothesis suggests that a few genes can have large additive effects on a quantitative trait?

    <p>Hypothesis 2</p> Signup and view all the answers

    What role does the environment play in determining phenotypes?

    <p>It modifies the phenotype alongside genotype</p> Signup and view all the answers

    Which term describes the phenotype resulting from incomplete dominance?

    <p>An intermediate phenotype distinct from both homozygous forms</p> Signup and view all the answers

    What does a quantitative trait locus (QTL) indicate?

    <p>Is masked by environmental interactions</p> Signup and view all the answers

    What is the main function of RPE65 in the context of vision?

    <p>To assist in the regeneration of visual pigments</p> Signup and view all the answers

    What condition is primarily associated with mutations in the RPE65 gene?

    <p>Hereditary retinal degeneration</p> Signup and view all the answers

    What was the outcome of the gene therapy trials on Briard dogs with RPE65 mutations?

    <p>Electroretinograms showed partial restoration of vision.</p> Signup and view all the answers

    In human clinical trials, what was the notable outcome at 12 months after RPE65 gene therapy?

    <p>Visual sensitivity improvements were maintained.</p> Signup and view all the answers

    What animal model is used to study the effects of RPE65 mutations on vision?

    <p>Briard dogs with congenital stationary night blindness</p> Signup and view all the answers

    What complication did Jesse experience four days after participating in the OTC gene therapy trial?

    <p>Massive immune reaction</p> Signup and view all the answers

    What was the primary function of the IL2 receptor gamma in the gene therapy trial for SCID X-linked?

    <p>Facilitate T-cell activation</p> Signup and view all the answers

    What potential outcome can occur if a transgene inserts into a proto-oncogene?

    <p>Expression leading to cancer</p> Signup and view all the answers

    Which cellular component was primarily targeted in the gene therapy trial involving CD34+ cells?

    <p>Precursor to lymphocytes</p> Signup and view all the answers

    Which gene is noted for its involvement in T-cell lymphoblastic Leukemia as a result of gene therapy?

    <p>LMO2 gene</p> Signup and view all the answers

    What is a characteristic symptom of Leber congenital amaurosis (LCA)?

    <p>Total blindness by age 30-40</p> Signup and view all the answers

    What type of experimental approach was suggested for identifying genes involved in Leber congenital amaurosis?

    <p>Candidate gene approach</p> Signup and view all the answers

    What is a significant challenge associated with gene therapy, as highlighted in the complications experienced by Jesse?

    <p>Unexpected immune reactions</p> Signup and view all the answers

    What are the potential effects of deletions on gene expression?

    <p>Larger deletions tend to have more severe effects.</p> Signup and view all the answers

    Which condition is characterized by the presence of an extra chromosome 21?

    <p>Down syndrome</p> Signup and view all the answers

    What factor increases the risk of having a child with Down syndrome?

    <p>Women becoming pregnant later in life</p> Signup and view all the answers

    What type of inversion does not include the centromere?

    <p>Paracentric inversion</p> Signup and view all the answers

    In which situation would a deletion mapping approach be most useful?

    <p>To locate mutations in genes</p> Signup and view all the answers

    What is the result of nonreciprocal translocation between chromosomes?

    <p>Only one chromosome loses genetic material while another gains it.</p> Signup and view all the answers

    What is the primary concern of prenatal screening tests?

    <p>To assess the risk of potential genetic diseases</p> Signup and view all the answers

    What does a Robertsonian translocation typically involve?

    <p>Swapping material between two acrocentric chromosomes.</p> Signup and view all the answers

    Which of the following describes how duplications can arise?

    <p>By misalignment during meiosis leading to unequal crossing over.</p> Signup and view all the answers

    What is the potential consequence of an inversion that includes a breakpoint within a gene?

    <p>Complete gene loss or inactivation</p> Signup and view all the answers

    Which statement about microarray analysis is true?

    <p>It allows for simultaneous detection of multiple genetic variations.</p> Signup and view all the answers

    How does the presence of a balancer chromosome affect Drosophila mutants?

    <p>It inhibits recombination, maintaining specific mutations.</p> Signup and view all the answers

    Which of the following chromosomal abnormalities is associated with male infertility?

    <p>Klinefelter syndrome</p> Signup and view all the answers

    What is typically assessed during fetal testing?

    <p>Presence of abnormal karyotypes</p> Signup and view all the answers

    What does Broad Sense Heritability (H2) indicate about a phenotype?

    <p>It reflects how much phenotypic variation is attributable to genetic variation in a population.</p> Signup and view all the answers

    Which component of genetic variation is considered predictive?

    <p>Additive effects (Va)</p> Signup and view all the answers

    Which of the following is true about Nonsense mutations?

    <p>They result in premature termination of protein synthesis.</p> Signup and view all the answers

    What does the Loss of Function mutation typically indicate?

    <p>The mutated gene results in no activity or reduced activity.</p> Signup and view all the answers

    How is Narrow Sense Heritability (h2) defined?

    <p>Proportion of phenotypic variation due to additive genetic variation.</p> Signup and view all the answers

    What type of mutation typically arises without a known mutagen?

    <p>Spontaneous mutation</p> Signup and view all the answers

    In McClintock's experiment, what is the role of the Ac element?

    <p>It activates the Ds element to cause breakage.</p> Signup and view all the answers

    What is a frameshift mutation likely to affect?

    <p>The sequence of codons downstream of the mutation.</p> Signup and view all the answers

    What defines transposable elements in eukaryotes?

    <p>They can move from one position to another in the genome.</p> Signup and view all the answers

    What is the importance of using quantitative trait loci (QTL) in genetic mapping?

    <p>To identify the genetic basis of complex traits.</p> Signup and view all the answers

    Which of the following describes a transition mutation?

    <p>A purine is replaced with another purine or a pyrimidine with another pyrimidine.</p> Signup and view all the answers

    What effect can mutations have on biosynthetic pathways?

    <p>They can halt the pathway from proceeding to final products.</p> Signup and view all the answers

    What is an example of a gain of function mutation?

    <p>A mutation causing a protein to be expressed at inappropriate times.</p> Signup and view all the answers

    Study Notes

    Additive Effects

    • Additive effects depend on the number of alleles present; a phenotypic effect can be 0, 1, or 2.
    • Frequency is highest in the middle of a Bell Curve graph.
    • Additive inheritance means that the contributions of each locus add up without any interactions or dominance/epistasis.

    Genetic Origins of Quantitative Traits

    • Hypothesis 1: Many loci with small equal and additive effects contribute to variation.
    • Hypothesis 2: A few genes with large additive effects influence variations.
    • Polygenic traits are solely influenced by genetics, multiple genes contribute to the trait.
    • Multifactorial traits are influenced by both genes and environmental factors.

    Environmental Effects

    • Environmental factors affect traits.
    • Phenotype (observable trait) = Genotype + Environment.
    • E.g. Siamese cats fur color changes due to temperature

    Quantitative Traits

    • Variation in traits influenced by genotype and additive effects.
    • Affected by environment and genotype.
    • Individual phenotypic classes can be masked by the environment.

    Calculating Heritability

    • Phenotypic variation is attributable to genetic and environmental factors.

    • Calculating broad sense heritability: H² = Vg/Vp (Vg=genetic variation, Vp=total phenotypic variation).

    • Narrow sense heritability: h² = Va/Vp (Va = additive genetic variation).

    • A high H² value (or h²) indicates that environment has minimal impact.

    • Heritability is specific to particular families or populations.

    Quantitative Trait Loci (QTL) Mapping

    • Identifying genes responsible for quantitative traits.
    • Genetic mapping and association of markers with traits.
    • Recombinant inbred lines (RILs) are used to identify chromosomes linked to traits.

    Mutations

    • Mutations are changes in the DNA sequence that can affect phenotype.
    • Classifications of mutations: base substitutions (transition or transversions), deletions, insertions, inversions, and reciprocal translocations.
    • Forward mutations: wild type → mutant Reverse mutations: mutant allele → wild type alleles.

    Molecular Consequences of Mutations

    • Silent (synonymous) mutations: do not change the amino acid sequence of a protein.
    • Missense mutations: change an amino acid sequence of a protein.
    • Nonsense mutations: change a codon to a stop codon, result in a shorter protein.
    • Frameshift: cause a change in the reading frame, resulting in a drastic change in a protein's structure.

    Epigenetic Modifications

    • Changes in gene expression, not due to alterations in the DNA sequence.
    • DNA methylation, histone modifications, and non-coding RNA influence gene expression
    • Hertiable changes over generations.
    • Imprinting: genes are expressed differently depending on whether they are inherited from mother or father.

    Chromosomal Abnormalities

    • Aneuploidy: having an abnormal number of chromosomes.
    • Monosomy: loss of one chromosome (2n-1).
    • Trisomy: gain of one chromosome (2n+1).
    • Polyploidy: having more than two complete sets of chromosomes. and their impact on phenotype.

    Transposable Elements (Transposons)

    • Segments of DNA that can move within a genome.
    • Transposition: occurs in different ways (e.g., retrotransposons which use RNA intermediates).
    • Effects on genomes and phenotype: can affect genes, create mutations, and sometimes be beneficial as they can lead to new variations.
    • Transposons can be studied in model organisms, often involving cytological studies.
    • How they are important in evolution/disease: play a role in evolution and potentially disease.

    Somatic Gene Therapy

    • Modification of somatic cells (not germline).
    • Used to treat a wide range of inherited and acquired diseases.
    • How it's related to model organisms, advantages and disadvantages.

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    Description

    Explore the intricate relationships between additive effects, genetic origins, and environmental influences on quantitative traits. This quiz delves into concepts like polygenic and multifactorial traits, shedding light on how both genetics and environment shape phenotypic variations. Test your understanding of these key genetic principles.

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