Chapter 4 - The Eukaryotic Cell Cycle, Mitosis and Meiosis
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Questions and Answers

What is the primary event occurring during prophase of mitosis?

  • Chromatids condense and become visible (correct)
  • Chromosomes align at the metaphase plate
  • Nuclear membrane reforms
  • Centrosomes move apart

    • Which phase of mitosis is characterized by the complete fragmentation of the nuclear envelope?

  • Prometaphase (correct)
  • Prophase
  • Anaphase
  • Telophase

    • In which phase do sister chromatids align at the metaphase plate?

  • Cytokinesis
  • Anaphase
  • Prophase
  • Metaphase (correct)

    • What happens during anaphase?

    <p>Chromatids are pulled towards the poles</p> Signup and view all the answers

    During which stage does the nuclear membrane re-form around the separated chromosomes?

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

    How does cytokinesis differ between animal and plant cells?

    <p>Animal cells form a cleavage furrow while plant cells form a cell plate</p> Signup and view all the answers

    What is the role of microtubules during cytokinesis?

    <p>They help in the formation of the cell plate in plants and cleavage plane in animals</p> Signup and view all the answers

    What is the final product of mitosis followed by cytokinesis?

    <p>Two daughter cells with identical genetic material</p> Signup and view all the answers

    What occurs during the G1 phase of the cell cycle?

    <p>The cell prepares for cell division.</p> Signup and view all the answers

    How are homologous chromosomes defined?

    <p>They are pairs of chromosomes that are nearly identical in size and genetic composition.</p> Signup and view all the answers

    During which phase of the cell cycle are sister chromatids formed?

    <p>S phase</p> Signup and view all the answers

    What is the total number of chromosomes in most human cells?

    <p>46</p> Signup and view all the answers

    What is the primary role of cytokinesis in cell division?

    <p>To divide the cytoplasm into two daughter cells.</p> Signup and view all the answers

    In which phase do cells enter a nondividing state?

    <p>G0 phase</p> Signup and view all the answers

    What happens to the chromosomes during mitosis?

    <p>They become compact enough to be seen.</p> Signup and view all the answers

    How does the chromosome theory of inheritance relate to cell division?

    <p>It describes how chromosomes are distributed to daughter cells.</p> Signup and view all the answers

    What characterizes eukaryotic chromosomes in human cells?

    <p>They occur in sets of 23.</p> Signup and view all the answers

    What variation is present between homologous chromosomes?

    <p>Differences in alleles provide genetic variation.</p> Signup and view all the answers

    What is the duration of the G1 phase for a cell that divides in 24 hours?

    <p>11 hours</p> Signup and view all the answers

    Which type of proteins control the advancement through the cell cycle?

    <p>Cyclins and cyclin-dependent kinases (cdks)</p> Signup and view all the answers

    During which phase does a cell spend the least amount of time in a typical 24-hour cell cycle?

    <p>M phase</p> Signup and view all the answers

    What do checkpoint proteins assess in a cell during the G1 checkpoint?

    <p>If the cell is in proper condition to divide</p> Signup and view all the answers

    Which checkpoint monitors the integrity of the spindle apparatus?

    <p>Metaphase checkpoint</p> Signup and view all the answers

    What happens when cyclins and cdks combine to form a complex?

    <p>They phosphorylate and activate proteins needed for the cell cycle</p> Signup and view all the answers

    How do cyclins behave during the cell cycle?

    <p>Their levels fluctuate</p> Signup and view all the answers

    Where do frog oocytes spend most of their time before maturation?

    <p>G2 phase</p> Signup and view all the answers

    What occurs during meiosis that results in genetic variation?

    <p>Formation of bivalents through synapsis</p> Signup and view all the answers

    How many chromosomes do gametes produced through meiosis in humans contain?

    <p>23</p> Signup and view all the answers

    What is the primary purpose of meiosis?

    <p>To generate haploid cells for reproduction</p> Signup and view all the answers

    Which stage of meiosis involves the segregation of homologous chromosomes?

    <p>Anaphase I</p> Signup and view all the answers

    During which phase of meiosis do bivalents align along the metaphase plate?

    <p>Metaphase I</p> Signup and view all the answers

    What is the result of crossing over during meiosis?

    <p>Physical exchange of chromosome segments</p> Signup and view all the answers

    What is the result of meiosis II?

    <p>Four haploid cells</p> Signup and view all the answers

    What is produced at the end of meiosis I?

    <p>Two haploid cells</p> Signup and view all the answers

    During which phase do sister chromatids separate in meiosis?

    <p>Anaphase II</p> Signup and view all the answers

    How does the alignment of chromosomes during metaphase I contribute to genetic diversity?

    <p>Through random assortment of maternal and paternal homologs</p> Signup and view all the answers

    What is the outcome of meiosis in terms of chromosome number?

    <p>It reduces the number of chromosomes by half, producing four haploid daughter cells.</p> Signup and view all the answers

    What describes the chromosome theory of inheritance?

    <p>The inheritance pattern of traits can be explained by chromosome behavior during meiosis.</p> Signup and view all the answers

    During meiosis, what happens to homologous chromosome pairs?

    <p>One chromosome from each pair is segregated into different daughter cells.</p> Signup and view all the answers

    What is the diploid number represented by 2n = 6?

    <p>6 chromosomes in 3 homologous pairs.</p> Signup and view all the answers

    What defines a gamete in terms of chromosome number?

    <p>It is a haploid cell that carries one set of chromosomes.</p> Signup and view all the answers

    Which of the following statements about meiosis is true?

    <p>Meiosis produces four genetically diverse haploid cells.</p> Signup and view all the answers

    Which modern principle of the chromosome theory states that chromosomes are passed from parent to offspring?

    <p>Chromosomes are replicated and passed from parent to offspring.</p> Signup and view all the answers

    What happens to chromosomes during the formation of haploid cells in meiosis?

    <p>Chromosomes segregate independently from each other.</p> Signup and view all the answers

    What is the physical location of a gene on a chromosome called?

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

    Which of the following best explains the advantage of sexual reproduction?

    <p>Allows for greater genetic variation</p> Signup and view all the answers

    In diploid-dominant species, what is the primary type of cell produced in reproductive organs?

    <p>Haploid gametes</p> Signup and view all the answers

    What is the process that creates a diploid cell called a zygote from two haploid gametes?

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

    Which life cycle involves a multicellular diploid stage and a multicellular haploid stage?

    <p>Alternation of generations</p> Signup and view all the answers

    What is a significant disadvantage of sexual reproduction?

    <p>Requires energy for courtship</p> Signup and view all the answers

    In which type of species do haploid cells unite to form a diploid zygote that undergoes meiosis immediately?

    <p>Haploid-dominant species</p> Signup and view all the answers

    Which term refers to the sequence of events that produces another generation of organisms?

    <p>Life cycle</p> Signup and view all the answers

    Which of the following statements is incorrect regarding gametes in sexual reproduction?

    <p>They are formed by mitosis</p> Signup and view all the answers

    In the life cycle of plants, what phase produces haploid spores?

    <p>Sporophyte phase</p> Signup and view all the answers

    Study Notes

    Eukaryotic Cell Cycle, Mitosis, and Meiosis

    • The human body contains between 10 to 50 trillion cells.
    • DNA sequences in all chromosomes in all cells are the same, except for rare mutations.
    • Cell reproduction ensures genetic material integrity through mitosis and meiosis.
    • A cell cycle is a highly regulated series of events that lead to cell division.
    • Chromosomes become compact enough to be viewed under a light microscope before cell division.
    • Cytogenetics is the field of genetics that involves examining chromosomes microscopically.

    Cell Division

    • The cell cycle has distinct phases: G1 (first gap), S (synthesis of DNA), G2 (second gap), and M (mitosis & cytokinesis).
    • G1: Cell growth and commitment to division, accumulating molecular changes for progression.
    • S: Each chromosome replicates, forming sister chromatids.
    • G2: Cell synthesizes proteins needed for chromosome sorting and division, and some growth might occur.
    • M: Mitosis divides a cell's nucleus into two, distributing duplicated chromosomes, and cytokinesis divides the cytoplasm into two daughter cells.
    • A cell may also exit the cell cycle and enter a nondividing phase G0.

    Cell Cycle Length

    • Cell cycle length varies among cell types. Embryos might have cell cycles measured in minutes, while adult cells can take several months to divide.
    • Fast dividing mammalian cells (like skin cells) have cell cycles between 10 to 24 hours.
    • Specific phases (G1, S, G2, and M) have specific durations within a 24 hour cell cycle.

    Control of the Cell Cycle

    • Cyclin/CDK protein complexes regulate cell cycle progression.
    • Cyclins fluctuate in levels during the cell cycle.
    • CDKs (cyclin-dependent kinases) are enzymes that activate other proteins—becoming active during specific phases.

    Cell Cycle Checkpoints

    • Checkpoint proteins control cell cycle progression to ensure proper conditions for division.
    • G1 checkpoint (restriction point) checks for favorable conditions and DNA damage.
    • G2 checkpoint checks for DNA damage and completeness of replication.
    • Metaphase checkpoint ensures proper spindle apparatus connection to chromosomes.

    Karyotype

    • Karyotype: A photographic representation of chromosomes.
    • Diagrams arranged according to chromosome size and banding patterns to enable identification of abnormalities or genetic defects.
    • For a diploid human cell, two sets of chromosomes from one cell constitute a karyotype of that cell.
    • Human cells are diploid, containing 46 chromosomes. 2 complete sets.
    • Gametes (sperm and eggs) are haploid, with one set of chromosomes= 23

    Homologs

    • In diploid species, members of a chromosome pair are called homologs or homologous chromosomes.
    • Homologous pairs are virtually identical in size and genetic composition, but have slight sequence differences responsible for genetic variation.
    • Most homologs differ by less than 1%.
    • Sex chromosomes (X & Y) differ significantly in size and genetic content.

    Mitosis

    • Mitosis produces two genetically identical daughter cells.
    • Mitosis involves the division of one nucleus into two nuclei and is followed by cytokinesis (division of the cell into two).
    • Asexual reproduction frequently uses mitosis in single-celled organisms. Mitosis is essential for development of multicelluar organisms.

    Mitosis Stages

    • Interphase—chromosome replication
    • Prophase—chromatid condensation, nuclear envelope fragmentation.
    • Prometaphase—spindle apparatus formation, attaching kinetochore microtubules to sister chromatids.
    • Metaphase—chromosomes align at the metaphase plate.
    • Anaphase—sister chromatids separate, with one going to each pole.
    • Telophase—chromosomes decondense, nuclear envelopes reform.
    • Cytokinesis—division of the cytoplasm.

    Cytokinesis

    • Cytokinesis is the division of the cytoplasm to form two daughter cells.
    • Cytokinesis differs in animals and plants.
    • Animal cells utilize a cleavage furrow.
    • Plant cells use a cell plate, that develops from Golgi vesicles and leads to a new cell wall.

    Meiosis

    • Meiosis produces four genetically unique haploid (n) daughter cells from one diploid (2n) cell.
    • Meiosis involves two rounds of cell division.
    • Meiosis is the process by which gametes are produced.

    Meiosis versus Mitosis

    • Meiosis and mitosis involve similar stages, however meiosis' unique stages increase genetic variation.
    • Mitosis involves one round of division, produces 2 diploid cells, and DNA replicates before the division.
    • Meiosis involves two rounds of division, produces 4 haploid cells, and DNA replicates only before the first division.

    Crossing Over

    • Crossing over is the exchange of genetic material between homologous chromosomes.
    • Crossing over occurs during the prophase I of Meiosis I.

    Meiosis I Stages

    • Prophase I: Homologous chromosomes pair up and exchange genetic material(crossing-over).
    • Prometaphase I: The nuclear envelope breaks down, and spindle fibers attach to chromosomes.
    • Metaphase I: Homologous pairs are aligned at the metaphase plate, in a double row.
    • Anaphase I: Homologous chromosomes separate and move toward opposite poles. Sister chromatids remain attached.
    • Telophase I: Chromosomes arrive in separate poles; nuclear membranes are reformed. Cytokinesis follows, resulting in 2 cells—each with one set of homologous chromosomes.

    Meiosis II Stages

    • Prophase II: Chromosomes condense. Nuclear envelope begins to dissociate.
    • Prometaphase II: Spindle apparatus forms, and kinetochores attach to sister chromatids.
    • Metaphase II: Sister chromatids are aligned at the metaphase plate.
    • Anaphase II: Sister chromatids separate, and each separated chromatid can now be considered a chromosome.
    • Telophase II/ Cytokinesis: Chromosomes arrive at opposite poles; nuclear membranes form. Cytokinesis separates the two cells into four new haploid cells.

    Chromosome Theory of Inheritance

    • Meiosis explains Mendel's laws of inheritance.
    • The chromosome theory of inheritance states that genes are located on chromosomes which are passed down from parent to offspring.
    • Homologous chromosomes segregation occurs during meiosis.
    • The pairing and segregating of homologs explain Mendelian traits.

    Sexual Reproduction

    • Sexual reproduction combines genetic material from two parents to create a diploid zygote.
    • After fertilization, mitosis produces numerous diploid cells, resulting in a multicelluar organism.
    • Sexual reproduction offers more genetic diversity.
    • Alternation in generations occurs in species where the life cycle alternates between a haploid cell or organism stage and a diploid cell or organism stage.

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