Biology Lecture 3: Chromosomes
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Questions and Answers

According to the lecture, what is the term for the complete set of genetic information in a haploid chromosome?

  • Diploid
  • Karyotype
  • Homologous chromosome
  • Genome (correct)

    • The lecture mentions that eukaryotic cells have a 'diploid number of chromosomes'. What does 'diploid' mean in this context?

  • Having one set of chromosomes
  • Having chromosomes that are all the same size and shape
  • Having two sets of chromosomes (correct)
  • Having a complete set of genetic information

    • Which of the following statements about homologous chromosomes is TRUE, based on the lecture?

  • They are identical chromosomes that pair during mitosis.
  • They are always located on the same chromosome arm.
  • They contain the same number and types of genes. (correct)
  • They are always the same size and shape.

    • According to the lecture, what is the term for chromosomes that do NOT pair during meiosis?

    <p>Nonhomologous chromosomes (C)</p> Signup and view all the answers

    The lecture emphasizes that diploid cells have two sets of chromosomes. Based on this information, what can you infer about haploid cells?

    <p>Haploid cells have one set of chromosomes. (A)</p> Signup and view all the answers

    What is the primary purpose of X-chromosome inactivation in female somatic cells?

    <p>To prevent the overproduction of proteins encoded by X-linked genes. (B)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of histones?

    <p>They are negatively charged proteins. (B)</p> Signup and view all the answers

    The Lyon Hypothesis explains which biological phenomenon?

    <p>Random inactivation of one X chromosome in female somatic cells. (A)</p> Signup and view all the answers

    What is the primary function of haploid (n) cells in sexual reproduction?

    <p>Production of gametes (sperm and egg cells) (A)</p> Signup and view all the answers

    Which of the following is NOT a key function of chromosomes?

    <p>Providing energy for cellular processes (D)</p> Signup and view all the answers

    Why is the packaging of DNA into chromosomes essential?

    <p>To prevent the DNA from tangling and becoming damaged. (B)</p> Signup and view all the answers

    What is the final level of compaction reached by DNA during the formation of a metaphase chromosome?

    <p>1400 nm fiber (D)</p> Signup and view all the answers

    What is the difference between the chromosome sets in haploid and diploid cells?

    <p>Haploid cells have a single set of chromosomes; diploid cells have two sets. (A)</p> Signup and view all the answers

    How are haploid cells produced?

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

    What is the significance of diploid cells in the context of growth and development?

    <p>Diploid cells allow for an organism to develop and maintain its tissues. (A)</p> Signup and view all the answers

    Why is the term 'chromosome' considered apt, given its composition?

    <p>Chromosomes are colored when stained, making them visible under a microscope. (A)</p> Signup and view all the answers

    What are the major components of a chromosome?

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

    Which of the following statements accurately describes the role of histones in a chromosome?

    <p>Histones help condense and organize DNA into a compact structure. (D)</p> Signup and view all the answers

    What is the function of telomeres?

    <p>To prevent the degradation of genetic material at the end of chromosomes (A)</p> Signup and view all the answers

    What is the name of the repeated sequence found in human telomeres?

    <p>5′-TTAGGG-3′ (B)</p> Signup and view all the answers

    What is the name of the structure formed by the telomere sequence folding back on itself?

    <p>T-loop (A)</p> Signup and view all the answers

    What is the role of the Shelterin complex in telomere maintenance?

    <p>To prevent the degradation of telomeres by nucleases (C)</p> Signup and view all the answers

    Why do telomeres shorten with each cell division?

    <p>Because DNA replication is not always complete at the ends of chromosomes (B)</p> Signup and view all the answers

    Which of the following cell types is likely to have high telomerase activity?

    <p>Skin cells (C)</p> Signup and view all the answers

    What is the relationship between telomere length and cellular senescence?

    <p>Shorter telomeres are associated with increased cellular senescence (B)</p> Signup and view all the answers

    What is a centromere's primary function during cell division?

    <p>To provide a point of attachment for spindle fibers, ensuring accurate chromosome segregation (A)</p> Signup and view all the answers

    What is the significance of repetitive DNA sequences in the centromere?

    <p>They increase the stability of the centromere. (B)</p> Signup and view all the answers

    What is the basis for classifying chromosomes into four groups (metacentric, submetacentric, acrocentric, and telocentric)?

    <p>The location of the centromere on the chromosome. (A)</p> Signup and view all the answers

    What does a karyotype provide a snapshot of?

    <p>The structure and arrangement of an individual's chromosomes (D)</p> Signup and view all the answers

    What is the purpose of cell culture in the karyotyping process?

    <p>To increase the number of cells for analysis. (C)</p> Signup and view all the answers

    What is the difference between autosomes and sex chromosomes?

    <p>Autosomes are involved in determining an individual's sex, while sex chromosomes control other traits. (A)</p> Signup and view all the answers

    How many chromosomes does a typical human cell contain?

    <p>46 (B)</p> Signup and view all the answers

    Why is karyotyping considered a 'golden method' for analyzing chromosomes?

    <p>It is the most accurate and reliable method. (C)</p> Signup and view all the answers

    Flashcards

    Haploid (n)

    A cell with one complete set of chromosomes, representing half the diploid number.

    Diploid (2n)

    A cell with two complete sets of chromosomes, one from each parent.

    Homologous chromosomes

    Pairs of chromosomes that are identical in shape, size, and genetic content.

    Genome

    The complete set of genetic information contained within a haploid chromosome.

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    Non-homologous chromosomes

    Chromosomes that have different genes and cannot pair up during meiosis.

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    X-Chromosome Inactivation

    In females, one X chromosome is randomly inactivated in somatic cells to prevent gene dosage imbalance.

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    Barr Body

    The inactive X chromosome in females that condenses into a dense structure.

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    Histones

    Proteins that DNA wraps around, aiding in the packaging of DNA into chromosomes.

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    DNA Packaging

    The process of condensing DNA into chromosomes, from a double helix to tightly packed structures.

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    Lyon Hypothesis

    The theory explaining the random inactivation of one X chromosome in females, ensuring equal gene dosage.

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    Chromosome Structure

    Thread-like structures made of DNA and proteins in the nucleus.

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    Meiosis

    A type of cell division producing haploid cells for sexual reproduction.

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    Mitosis

    A type of cell division that produces diploid cells for growth and repair.

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    Somatic Cells

    Diploid cells that make up most of the body, containing two sets of chromosomes.

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    Haploid Examples

    Gametes such as sperm and egg cells that contain one set of chromosomes (23).

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    Diploid Examples

    Regular body cells that contain two sets of chromosomes (46).

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    Chromosome Function

    Protect DNA, regulate gene access, and conserve space in cells.

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    Importance of Chromosomes

    Vital for genetic information storage, ensuring proper cell function.

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    Centromere

    The central region of a chromosome that joins sister chromatids.

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    Telomeres

    Repetitive DNA sequences at the ends of linear chromosomes that protect genetic material.

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    Sister Chromatids

    Identical copies of a chromosome formed after DNA replication.

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    Biparental Inheritance

    Inheritance of nuclear DNA from both mother and father.

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    Maternal Inheritance

    Inheritance of mitochondrial DNA solely from the mother.

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    T-Loop

    Structure formed by telomeres folding back to protect themselves.

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    Shelterin Complex

    A group of proteins that protects telomeres from being recognized as damaged.

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    Telomerase

    An enzyme that prevents telomeres from shortening during cell division.

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    Types of Chromosomes

    Chromosomes are classified as metacentric, submetacentric, acrocentric, and telocentric based on centromere location.

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    Human Karyotype

    A representation of all chromosomes in an individual, showing number and type.

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    Total Chromosomes in Humans

    Humans have 46 total chromosomes organized into 23 pairs.

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    Autosomes

    Chromosomes not involved in sex determination; there are 22 pairs in humans.

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    Sex Chromosomes

    The pair of chromosomes that determine an individual's sex; X and Y in humans.

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    Karyotyping Process

    Pairing and ordering all chromosomes to analyze genetic information.

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    Chromosome Pairing in Humans

    Pairs consist of 22 autosomes plus one sex chromosome pair (XX or XY).

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    Study Notes

    Lecture 3: Chromosomes

    • Walther Flemming's work in the 1880s marked the beginning of the discovery and identification of human chromosomes.
    • Eukaryotic cells have a diploid number of chromosomes.
    • The complete set of genetic information in a haploid chromosome is known as the genome.
    • Homologous chromosomes are identical chromosome pairs appearing during meiosis.
    • Homologous chromosomes have the same number and types of genes.
    • Some chromosomes are non-homologous and cannot pair.

    Lecture Objectives

    • Differentiate between haploid (n) and diploid (2n)
    • Identify key aspects of chromosomes
    • Classify chromosomes
    • Understand the human karyotype
    • Understand the Lyon hypothesis (X-chromosome inactivation)
    • Identify how DNA packs to form chromosomes

    Haploid (n) and Diploid (2n) Key Concepts

    • Eukaryotic cells possess a diploid number of chromosomes.
    • The complete set of genetic information in a haploid chromosome is referred to as the genome.
    • Homologous chromosomes are identical and pair during meiosis.
    • Homologous chromosomes share similar gene numbers and types.

    Key Differences Between Haploid and Diploid

    Feature Haploid (n) Diploid (2n)
    Chromosome Sets One set (n) Two sets (2n)
    Example in Humans Sperm and egg cells (23 chromosomes) Somatic cells (46 chromosomes)
    Type of Division Produced by meiosis Produced by mitosis
    Function Sexual reproduction Growth, repair, and development

    Key Aspects of Chromosomes

    • Chromosomes are thread-like structures within the nucleus made of DNA and proteins (primarily histones).
    • The DNA is wrapped around proteins to protect it and regulate gene access.
    • Chromosomes are essential for conserving space in cells.

    Chromosomes Structure

    • Each chromosome has a centromere (central region), telomeres (protective ends), and two identical sister chromatids (after DNA replication).
    • Chromatin condenses during cell division to form visible chromosomes.

    Nuclear and Mitochondrial DNA

    • Nucleus chromosomes are linear and inherit from both parents (biparental inheritance).
    • Mitochondrial chromosomes are circular and inherit only from the mother (maternal inheritance).

    Telomeres

    • Telomeres are repetitive DNA sequences at the ends of linear chromosomes.
    • They act as protective caps, preventing degradation of genetic material and maintaining chromosome stability during cell division.
    • In humans, the telomere sequence is 5'-TTAGGG-3' (repeated approximately 2000 times).
    • Telomeres form T-loops which are maintained by the Shelterin Complex (protein shield)
    • The shortening of telomeres leads to cell death.
    • Telomerase, an enzyme, prevents telomere shortening.

    What Is a Centromere?

    • It is the point where sister chromatids join and where spindle fibers attach for accurate chromosome segregation.
    • Composed of repetitive DNA sequences.

    Classify Chromosomes

    • Chromosomes are classified based on centromere location (metacentric, submetacentric, acrocentric, and telocentric).

    Understand the Human Karyotype

    • Karyotyping is the process of pairing and ordering all chromosomes for a genome-wide view of an individual's chromosomes. It uses cell staining to visualize chromosomes; allows identification of chromosome abnormalities or genetic disorders.
    • Scientists use size, banding patterns, and centromere positions to identify chromosomes.
    • A human karyotype shows the number and types of chromosomes; normally, 46 chromosomes in somatic cells.
    • Autosomes are chromosomes not associated with sex determination.
    • Sex chromosomes (X and Y) determine sex. The X chromosomes are crucial in determining sex, and the X and Y chromosomes are placed from 1 to 22 chromosomes in a human karyotype in descending order of size.

    X-Chromosome Inactivation

    • In female somatic cells, only one X chromosome is active and the other X-chromosome is inactivated to regulate dosage compensation between males and females.
    • This inactivation happens randomly during early embryonic life
    • The inactivated X chromosome is visible as a Barr body.

    DNA Packing to Make Chromosomes

    • DNA packaging starts as a simple 2 nm double helix, progressing through multiple levels of compaction to form a 1400 nm metaphase chromosome.
    • This hierarchical structure allows nearly 2 meters of DNA to fit inside a microscopic cell nucleus.
    • DNA wraps around proteins called histones to form nucleosome structures. This is a fundamental level of chromosome organization.

    What Are Histones?

    • Histones are basic, positively charged proteins that package DNA tightly.
    • Five main histone types exist (core and linker histones).

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    Explore the fundamental concepts of chromosomes in this quiz based on Lecture 3. You'll learn about haploid and diploid cells, the structure and classification of chromosomes, and the human karyotype. Test your understanding of key terms and hypotheses related to chromosomes.

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