Sex Chromosomes and Sex Linkage
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Questions and Answers

What role does the trp repressor play in gene expression?

  • It binds to enhancer regions to increase transcription.
  • It promotes the production of tryptophan by activating genes.
  • It enhances transcription by binding to the operator.
  • It prevents RNA polymerase from transcribing downstream genes. (correct)

    • What is the function of the TATA box in eukaryotic transcription?

  • It facilitates RNA polymerase binding to the promoter. (correct)
  • It acts as a silencer region for gene repression.
  • It serves as a binding site for activators.
  • It enhances the binding of transcriptional repressors.

    • Which structural motif is often associated with transcriptional activators?

  • Zinc finger
  • Helix-turn-helix
  • Helix-loop-helix (correct)
  • Leucine zipper

    • How do certain repressors regulate gene transcription in eukaryotes?

    <p>By binding to silencing regions of DNA. (C)</p> Signup and view all the answers

    What are transcription factors primarily responsible for in eukaryotic cells?

    <p>Regulating the transcription of genes. (C)</p> Signup and view all the answers

    What type of mutation introduces a stop codon into the sequence, terminating translation prematurely?

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

    Which mutation type involves the deletion or addition of a base pair, causing a shift in the reading frame?

    <p>Frameshift mutation (D)</p> Signup and view all the answers

    What is the primary function of DNA Polymerase III during DNA replication?

    <p>Proofread nucleotides and facilitate strand elongation (C)</p> Signup and view all the answers

    Which of the following statements is correct regarding mutations in introns?

    <p>They have little to no effect on the resulting protein. (B)</p> Signup and view all the answers

    What type of mutation involves a segment of DNA being removed and not replaced?

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

    Which enzyme is responsible for repairing errors that occur within DNA strands?

    <p>DNA Polymerase II (B)</p> Signup and view all the answers

    What effect does a silent mutation have on a protein?

    <p>No change in the amino acid sequence (D)</p> Signup and view all the answers

    Which type of chromosomal mutation involves a segment of DNA being flipped in orientation?

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

    What does the recombination frequency of linked genes help determine?

    <p>The distance of their loci from each other (A)</p> Signup and view all the answers

    Which component is NOT part of a nucleotide in DNA?

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

    During which phase of the cell cycle does DNA replication occur?

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

    What is the main function of DNA Ligase during replication?

    <p>Joins Okazaki fragments (B)</p> Signup and view all the answers

    What is the end-product of transcription?

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

    Which step of transcription involves RNA Polymerase binding to the promoter?

    <p>Initiation (D)</p> Signup and view all the answers

    What process removes introns from the mRNA transcript?

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

    Which modification helps protect mRNA from degradation?

    <p>5’ cap (B)</p> Signup and view all the answers

    The enzyme responsible for synthesizing telomeres is called?

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

    Which of the following occurs during mRNA processing in eukaryotes?

    <p>Removal of introns (D)</p> Signup and view all the answers

    Which of the following correctly describes the direction of elongation during transcription?

    <p>5’ to 3’ on the new RNA strand (B)</p> Signup and view all the answers

    What is the typical consequence of mutations in DNA?

    <p>They can lead to changes in the protein expressed (C)</p> Signup and view all the answers

    Which enzyme is primarily responsible for adding complementary DNA nucleotides during replication?

    <p>DNA Polymerase III (A)</p> Signup and view all the answers

    Flashcards

    Point Mutation

    Changes in a single nucleotide base pair within DNA.

    Silent Mutation

    A point mutation that does not alter the amino acid sequence.

    Missense Mutation

    A point mutation where a single base change codes for a different amino acid in the protein.

    Nonsense Mutation

    A point mutation that changes a codon for an amino acid into a stop codon.

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    Frameshift Mutation

    A mutation where insertion or deletion of bases shifts the reading frame of the genetic code.

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    DNA Polymerase III

    Enzyme that replicates DNA and has proofreading ability.

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    DNA Polymerase II

    DNA repair enzyme.

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    Mutagen

    An agent that causes mutations.

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    Trp Operon Regulation

    The Trp operon produces more tryptophan, activates repressor molecules. The repressor binds to the operator, preventing RNA polymerase from transcribing genes.

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    Eukaryotic Gene Regulation

    Controlled primarily by transcription factors that bind to DNA. Requires a pre-initiation complex and general transcription factors to assemble RNA polymerase on the promoter.

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    TATA Box

    Part of eukaryotic promoters, where general transcription factors bind.

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    Transcription Factors

    DNA-binding proteins influencing the rate of transcription, some activate, some repress.

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    DNA-binding motifs

    Specific 3D structures in proteins that help them bind to DNA. Examples include helix-turn-helix and helix-loop-helix.

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    Sex chromosomes in mammals

    XX/XY system where XX individuals are female and XY individuals are male.

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    Sex chromosomes in birds

    ZZ/ZW system where ZZ individuals are male and ZW individuals are female.

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    Sex chromosomes in arachnids, insects

    XX/X0 system where XX is female and X0 is male.

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    Haplodiploidy chromosomes

    Bees, ants, wasps: diploid females, haploid males.

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    Sex-linked traits

    Traits coded by genes on the X chromosome, with different inheritance patterns from autosomal traits.

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    Male hemizygous

    Males having only one X chromosome.

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    Colorblindness

    Often a sex-linked recessive trait, more common in males.

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    DNA nucleotides

    Monomers of DNA comprised of a sugar, phosphate, and a nitrogenous base.

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    DNA Replication Location

    Occurs in the nucleus during the 'S' phase of the cell cycle.

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    Helicase (DNA replication)

    Unwinds the DNA double helix at the replication fork.

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    Polymerase III (DNA replication)

    Builds new DNA strands adding nucleotides 5' to 3'.

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    Transcription location - Prokaryotes

    Occurs in the cytoplasm of prokaryotic cells.

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    mRNA processing (introns)

    Non-coding regions of mRNA removed during processing.

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    Transcription initiation

    RNA polymerase binds to the promoter region of the DNA.

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    Translation Location - Eukaryotes

    Occurs in the cytoplasm and rough ER.

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    Study Notes

    Sex Chromosomes

    • Found in most mammals and some insects
    • XX individuals typically possess a female phenotype
    • XY individuals typically possess a male phenotype
    • Males have one X chromosome, thus called hemizygous (half)
    • The SRY region on the Y chromosome influences male sex differentiation
    • ZZ individuals typically possess a male phenotype
    • ZW individuals typically possess a female phenotype
    • Females have one Z chromosome, thus called hemizygous zero
    • XX/X0 is found in many insects.
    • XX individuals in XX/X0 have a female phenotype
    • X0 individuals in XX/X0 have a male phenotype
    • The "0" indicates that no other sex chromosome is present
    • Haplodiploidy: found in bees, ants, wasps and some other insects.
    • Diploid individuals (from fertilized eggs) possess a female phenotype
    • Haploid individuals (from unfertilized eggs) possess a male phenotype

    Sex Linkage

    • Sex-linked traits are coded for by genes on the X chromosome
    • Males have a single X chromosome, expressing these traits regardless of dominance or recessiveness
    • Makes males more vulnerable to conditions caused by sex-linked genes
    • Example: color blindness which is a recessive trait often appears in males.
    • Females can be color blind, but it is less common

    Gene Linkage & Mapping

    • Gene linkage and mapping can determine the distance between loci (specific locations) of genes on chromosomes by observing linkage frequency.

    DNA Structure

    • Phosphodiester bonds link nucleotides to form nucleic acids (DNA and RNA)
    • Nucleotides include: a 5-carbon sugar (hexose), phosphate group, and a nitrogenous base.
    • DNA sugar: Deoxyribose
    • RNA sugar: Ribose
    • Purines: Adenine (A) and Guanine (G)
    • Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)

    DNA Replication

    • Location: Nucleus
    • Time: S phase of the cell cycle
    • Proteins/Enzymes involved
      • Helicase: unwinds DNA double helix
      • Single-strand binding proteins (SSBs): prevent separated strands of DNA from re-attaching
      • Topoisomerase/DNA gyrase: relaxes DNA double helix tension
      • Primase: creates RNA primers at the origin of replication
      • DNA polymerase III builds new DNA strands in 5' to 3' direction, proofreading 3' to 5'
      • DNA polymerase I removes RNA primer and replaces with DNA
      • DNA Ligase: seals gaps between Okazaki fragments

    Gene Expression, Transcription, & mRNA Processing

    • Transcription:
      • Location: Prokaryotes: cytoplasm, Eukaryotes: nucleus
      • RNA polymerase binds to the promoter region.
      • Elongation: builds mRNA strand 3' → 5'
      • Termination: polymerase reaches terminator region and stops
    • mRNA Processing:
      • Primarily in eukaryotes
      • Introns (non-coding regions) are removed.
      • Exons (coding regions): are joined
      • 5' cap and 3' poly-A tail are added to mRNA

    rRNA Charging & Translation

    • tRNA Charging: tRNA synthetase enzymes bind tRNA molecules to specific amino acids, using ATP.
    • Translation: Synthesis of polypeptides (proteins), location is eukaryotes: cytoplasm,rough ER. Requires ribosomes

    Mutations & DNA Repair

    • Mutations: changes in DNA sequence, spontaneous changes or caused by mutagens
    • Types: point mutations - silent (no change), missense (different amino acid), nonsense (stop codon), frameshift (insertions/deletions)
    • DNA repair mechanisms exist, including those involving DNA Polymerase III

    Regulation of Gene Expression (Prokaryotes)

    • Negative regulation: repressor binds, prevents gene expression
    • Positive regulation: activator binds, promotes expression
    • Inducible system: gene normally off, but can be switched on by the presence of an inducer (e.g., lactose in the lac operon).
    • Repressible system: gene normally on, but can be turned off by a corepressor (e.g., tryptophan in the trp operon).

    Regulation of Gene Expression (Eukaryotes)

    • Primarily controlled by transcription factors
    • Transcription factors bind to enhancer regions to increase transcription rate
    • Repressors bind to silencing regions to decrease transcription

    DNA-Binding Proteins

    • Utilize structural motifs (e.g., helix-turn-helix, helix-loop-helix) to interact with DNA
    • These motifs are often associated with specific functions (e.g., repressors or activators).

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    Concept Check Exam 4 PDF

    Description

    This quiz covers the fundamentals of sex chromosomes and sex linkage, highlighting the differences in phenotypes between XX, XY, ZZ, and ZW individuals. It also delves into unique concepts like hemizygosity and haplodiploidy. Test your understanding of these essential genetics principles!

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