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What is one reason why Mendel chose garden peas for his experiments?

  • Peas are large plants that require extensive care.
  • Many varieties of pea plants were available. (correct)
  • Peas only produced one type of offspring.
  • Peas could grow in a variety of climates.

    • What is a monohybrid cross?

  • A cross to study two traits at once.
  • A cross involving only two variations of a single trait. (correct)
  • A cross aimed at producing hybrid strains.
  • A cross between plants of different species.

    • Which of the following characteristics of peas contributed to Mendel's studies?

  • They are difficult to cross-fertilize.
  • They have a long growing season.
  • They produce large amounts of seeds.
  • They can self-fertilize or be cross-fertilized. (correct)

    • What was the first step Mendel took in his experimental method?

    <p>Produce true-breeding strains for each trait.</p> Signup and view all the answers

    What do Cdks primarily regulate in the cellular process?

    <p>Cell cycle control</p> Signup and view all the answers

    How many different traits did Mendel study during his experiments on pea plants?

    <p>Seven traits</p> Signup and view all the answers

    Which complex is also referred to as the mitosis promoting factor (MPF)?

    <p>Cdk-cyclin complex</p> Signup and view all the answers

    What role does phosphorylation play in the activity of Cak?

    <p>It can both activate and inactivate Cak depending on the site</p> Signup and view all the answers

    Which CdK-cyclin complex is associated with the G2/M transition?

    <p>G2/M-Cdk1/cyclin B</p> Signup and view all the answers

    Which checkpoint involves evaluating the presence of all chromosomes at the metaphase plate?

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

    What is the primary function of the anaphase promoting complex (APC)?

    <p>Trigger anaphase</p> Signup and view all the answers

    What cellular event is described by the process of cellular proliferation?

    <p>Cells growing and dividing to create new cells</p> Signup and view all the answers

    What happens when tumor-suppressor genes are mutated?

    <p>Cell division occurs uncontrollably</p> Signup and view all the answers

    During which phase does a cell commit to DNA replication?

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

    What is the primary role of growth factors in cell division?

    <p>To signal for cells to grow or divide</p> Signup and view all the answers

    What happens at the G2/M checkpoint if there is DNA damage?

    <p>The cell halts DNA replication</p> Signup and view all the answers

    What is assessed by the spindle checkpoint before chromosome separation?

    <p>The attachment of all kinetochores to the spindle</p> Signup and view all the answers

    What does genomic fidelity refer to during DNA replication?

    <p>The accuracy of DNA replication</p> Signup and view all the answers

    What is the main role of the p53 protein in the cell cycle?

    <p>To monitor DNA integrity and facilitate repairs</p> Signup and view all the answers

    What happens if p53 detects irreparable DNA damage?

    <p>It causes the cell to self-destruct</p> Signup and view all the answers

    What is an effect of mutations in proto-oncogenes?

    <p>They can lead to cancer by becoming oncogenes</p> Signup and view all the answers

    During which phase of meiosis does crossing over occur?

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

    What is a characteristic of haploid cells?

    <p>They have one set of chromosomes</p> Signup and view all the answers

    What is the main outcome of meiosis I?

    <p>Reduction of chromosome number to haploid</p> Signup and view all the answers

    Which process fails during nondisjunction?

    <p>Separation of chromosomes to opposite poles</p> Signup and view all the answers

    What primarily characterizes the male reproductive system in humans?

    <p>Production of sperm in seminiferous tubules</p> Signup and view all the answers

    Which phase of meiosis is referred to as the reduction division?

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

    What role do chiasmata play during meiosis?

    <p>Facilitate genetic recombination between chromatids</p> Signup and view all the answers

    What is the result of cytokinesis following telophase II of meiosis?

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

    How do somatic cells differ from germ-line cells in terms of chromosome sets?

    <p>Somatic cells have two sets of chromosomes</p> Signup and view all the answers

    What predominantly happens in the prophase I stage of meiosis?

    <p>Homologous chromosomes undergo synapsis and crossing over</p> Signup and view all the answers

    What primarily composes a nucleosome?

    <p>200 DNA nucleotides coiled around 8 histone proteins</p> Signup and view all the answers

    During interphase, what structure do nuclear zones wrap into?

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

    What is the main difference between chromatin during interphase and mitosis?

    <p>Chromatin is inactive during mitosis.</p> Signup and view all the answers

    What are homologous chromosomes?

    <p>Pairs of the same kind of chromosome</p> Signup and view all the answers

    Which phase of mitosis involves the alignment of chromosomes along the metaphase plate?

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

    What happens to the sister chromatids during anaphase?

    <p>They are pulled to opposite poles.</p> Signup and view all the answers

    What structure is formed between the nuclei in plant cells during cytokinesis?

    <p>Cell plate</p> Signup and view all the answers

    What is the role of cohesin proteins during mitosis?

    <p>Aid in the separation of sister chromatids</p> Signup and view all the answers

    What occurs at the G1/S checkpoint of the cell cycle?

    <p>Cell decides whether or not to divide</p> Signup and view all the answers

    How many phases are there in mitosis?

    <p>5</p> Signup and view all the answers

    What role do condensin proteins play during mitosis?

    <p>They aid in chromatin compaction.</p> Signup and view all the answers

    What is a karyotype?

    <p>An array of chromosomes of an individual organism</p> Signup and view all the answers

    Which phase follows prometaphase in cell division?

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

    Study Notes

    Gregor Mendel's Pea Plant Experiments

    • Mendel crossed two varieties of garden peas, Pisum sativum.
    • He chose peas because they were small, easy to grow, and could self-fertilize or be cross-fertilized.
    • Mendel designed his experiments in three stages:
      • He produced true-breeding strains for each trait he was studying.
      • He cross-fertilized true-breeding strains that had alternate forms of the trait (reciprocal crosses were also performed).
      • He allowed hybrid offspring to self-fertilize for several generations and counted the number of offspring showing each form of the trait.
    • Mendel's experiments focused on monohybrid crosses, which involve only two variations of a single trait.
    • He studied seven different traits, each with two distinct variants.

    Cell Cycle Control and Cyclin-Dependent Kinases (Cdks)

    • Cdks are the primary mechanism of cell cycle control.
    • Cdks partner with different cyclins at different points in the cell cycle.
    • Cdk-cyclin complexes are also called mitosis promoting factors (MPFs).
    • The activity of Cdks is controlled by phosphorylation.
    • Phosphorylation at one site inactivates Cdk, while phosphorylation at another site activates it.
    • Multiple Cdks control the cell cycle.

    Mammalian Cell Cycle Control

    • In mammalian cells, specific Cdk-cyclin complexes regulate different stages of the cell cycle:
      • G1/S-Cdk2/cyclin E
      • G2/M-Cdk1/cyclin B
    • The spindle checkpoint ensures that all chromosomes are at the metaphase plate and that there is tension on the microtubules between opposite poles.
    • The anaphase promoting complex (APC) is involved in the spindle checkpoint.
    • APC triggers anaphase itself.

    Cellular Proliferation

    • Cellular proliferation is the process by which cells grow and divide to create new cells, increasing the number of cells.
    • Growth factors specify cell surface receptor signaling reactions that trigger Cdk proteins to start cell division.
    • When mutated, two types of genes can disturb the cell cycle:
      • Tumor-suppressor genes: Control cell growth.
      • Proto-oncogenes: Regulate cell cycle control.

    p53 Protein

    • p53 plays a key role in the G1 checkpoint.
    • The p53 protein monitors the integrity of DNA.
    • If DNA is damaged, cell division is halted, and repair enzymes are stimulated.
    • If DNA damage is irreparable, p53 directs the cell to kill itself.
    • p53 is often absent or damaged in cancerous cells.

    Retinoblastoma Susceptibility (Rb)

    • Rb is a tumor-suppressor gene.
    • Mutations in Rb predispose individuals to retinoblastoma, a rare form of cancer that affects the retina of the eye.

    Proto-oncogenes

    • These are normal cellular genes that become oncogenes (cancer-causing genes) when mutated.

    Sexual Life Cycle

    • Somatic cells are diploid.
    • Somatic cells undergo mitosis to form two genetically identical daughter cells.
    • Somatic cells of adults have two sets of chromosomes.
    • Germ-line cells are diploid.
    • Germ-line cells undergo meiosis to produce haploid gametes after puberty.
    • Offspring inherit genetic material from two parents.
    • Haploid sperm + haploid egg = diploid zygote.

    Meiosis

    • Meiosis consists of two rounds of division: meiosis I and meiosis II.
    • Before meiosis, homologous chromosomes become closely associated ("synapsis").
    • Chiasmata, the sites of crossing over, form during synapsis.
    • Genetic recombination occurs between non-sister chromatids.
    • The first meiotic division is termed the "reduction division".
    • Meiosis I forms haploid cells.
    • Meiosis II does not reduce chromosome number.
    • Meiosis II separates sister chromatids for each homologue.

    Meiosis Phases

    • Meiosis I:
      • Prophase I: Chromosomes coil tightly, the nuclear envelope disappears, and the spindle forms. Each chromosome is composed of two sister chromatids. Synapsis occurs, and crossing over takes place between non-sister chromatids.
      • Metaphase I: Terminal chiasmata hold homologues together. Microtubules from opposite poles attach to each homologue. Homologues are aligned at the metaphase plate.
      • Anaphase I: Microtubules shorten, and homologues are separated from each other and move to opposite poles.
      • Telophase I: Nuclear envelope reforms around each daughter nucleus. Cytokinesis may or may not occur after telophase.
    • Meiosis II:
      • Prophase II: The nuclear envelope dissolves, and a new spindle apparatus forms.
      • Metaphase II: Chromosomes align on the metaphase plate.
      • Anaphase II: Sister chromatids are separated from each other.
      • Telophase II: Nuclear envelope reforms around four sets of daughter chromosomes; cytokinesis follows.

    Final Result of Meiosis

    • Meiosis produces four cells containing haploid sets of chromosomes.

    Meiosis Errors

    • Nondisjunction: Failure of chromosomes to move to opposite poles during either meiotic division.
    • Aneuploid gametes: Gametes with missing or extra chromosomes.

    Unique Aspects of Meiosis

    • Synapsis and crossing over occur.
    • Sister chromatids remain joined at their centromere throughout meiosis.
    • Kinetochores of sister chromatids attach to the same pole in meiosis I.
    • DNA replication is suppressed between meiosis I and meiosis II.

    Human Female Reproductive System

    • At puberty, granulosa cells secrete estrogen.
    • At birth, ovaries contain about 1 million follicles.
    • The human menstrual cycle lasts about 1 month.

    Human Male Reproductive System

    • Seminiferous tubules are the sites of sperm production.
    • Leydig cells produce testosterone.

    Sexual Activity and Disease Transmission

    • There are 15 million new sexually transmitted infections (STIs) in the USA each year.
    • More than 25 diseases are primarily spread through sexual activity.

    Nucleosome Structure

    • A nucleosome is a complex of DNA and histone proteins that promote DNA coiling.
    • It consists of 200 DNA nucleotides coiled around a core of eight histone proteins.
    • Histone proteins are positively charged, while phosphate groups on DNA are negatively charged.

    Chromatin Structure

    • Interphase: The chromatin in the non-dividing nucleus is wrapped into higher-order coils called solenoids, forming a 30 nm fiber.
    • Mitosis: During mitosis, solenoids are arranged around a scaffold of protein for maximum compaction, aided by condensin proteins.
    • Compacted chromatin is inactive, while unpacked chromatin is active.

    Karyotype

    • A karyotype is an array of chromosomes of an individual organism.
    • Chromosomes are arranged by size, staining properties, and location of the centromere.
    • Humans are diploid (2n) with two sets of chromosomes.
    • Haploid (n) refers to one set of chromosomes, which is 23 in humans.
    • Homologous chromosomes are pairs of the same kind of chromosome.

    Cell Cycle Stages

    • Interphase: The longest phase of the cell cycle, divided into three sub-phases.
      • G1: Major growth of the cell.
      • S: Replication of DNA.
      • G2: Organelles replicate, microtubules organize, and final preparations for mitosis are made.
    • M (Mitosis): Separation of the nucleus, subdivided into five phases (prophase, prometaphase, metaphase, anaphase, telophase).
    • C (Cytokinesis): Separation of cytoplasm to form new cells.

    Centromere Structure

    • The centromere is the point of constriction on a chromosome.
    • The kinetochore is the attachment site for microtubules on the centromere.
    • Each sister chromatid has a centromere.
    • Sister chromatids remain attached at the centromere by cohesin.

    Mitosis Phases

    • Prophase: Chromosomes condense, spindles begin to form, and the nuclear envelope breaks down.
    • Prometaphase: After nuclear envelope disassembly, microtubules attach to chromosome kinetochores. Chromosomes start moving to the center of the cell.
    • Metaphase: Alignment of chromosomes along the metaphase plate, the axis of cell division.
    • Anaphase: Removal of cohesin proteins, centromeres split, and sister chromatids are pulled to opposite poles.
      • Anaphase A: Kinetochores are pulled toward the poles.
      • Anaphase B: Spindle poles move apart.
    • Telophase: The spindle disassembles, a new cytoskeleton forms, a nuclear envelope forms around each set of sister chromatids (now called chromosomes), chromosomes begin to uncoil, the nucleolus reappears, and mitosis is completed.

    Cytokinesis

    • Animal Cells: Constriction of actin filaments produces a cleavage furrow.
    • Plant Cells: A cell plate forms between the nuclei.

    Cell Cycle Checkpoints

    • The cell cycle has two irreversible points: replication of genetic material and separation of sister chromatids.
    • Cell cycle checkpoints allow the cycle to be put on hold at specific points:
      • G1/S Checkpoint: The cell "decides" to divide.
      • G2/M Checkpoint: Ensures DNA replication is complete and that there is no DNA damage.
      • Spindle Checkpoint: Ensures that all chromosomes are properly attached to the spindle microtubules before anaphase.

    Cell Cycle Checkpoints

    • G1 Checkpoint: The cell commits to DNA replication in the S phase.
      • Growth factors are peptides that signal for cells to grow and divide.
      • The G1 checkpoint halts the cell cycle in the presence of DNA damage, starvation conditions, or a lack of growth factors.

    G2/M Checkpoint

    • The cell commits to mitosis and assesses the success of DNA replication.
      • The G2/M checkpoint halts the cell cycle if DNA damage is detected.
      • Genomic fidelity refers to the accuracy of DNA replication.

    Spindle Checkpoint

    • The cell ensures that all chromosomes are attached to the spindle before proceeding to anaphase.
      • The spindle checkpoint halts the cell cycle if not all kinetochores are attached to the spindle.
      • The cell commits to separating chromosomes during anaphase.

    Decision Points

    • The cell cycle is regulated at checkpoints that assess the readiness of the cell to proceed to the next stage.
    • These checkpoints ensure that the cell has successfully replicated its DNA and that the environment is favorable for cell division.
    • The key decision points are:
      • Is DNA replicated accurately?
      • Are growth factors present?
      • Is the environment favorable?

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