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Cell Division and Early Development - Anatomy & Physiology

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Terms in this set (26)

  • What are somatic cells?
    Somatic cells are all body cells except sex cells (sperm and egg). Humans have 23 chromosome pairs in somatic cells, totaling 46 chromosomes.
  • What is the difference between homologous chromosomes and sex chromosomes?
    22 pairs are homologous (same genes, possibly different alleles). The 23rd pair are sex chromosomes: XX in females, XY in males.
  • Define haploid and diploid numbers in humans.
    Haploid (n) is 23 chromosomes (one set). Diploid (2n) is 46 chromosomes (two sets, one from each parent).
  • What are the two main stages of the cell cycle?
    1. Interphase: cell growth and DNA replication. 2. Mitotic phase (M phase): mitosis (nuclear division) and cytokinesis (cytoplasmic division).
  • What happens during the G1 phase of interphase?
    G1 lasts 8-10 hours with intense growth and metabolism. Centrosomes replicate. Cells not dividing remain in G0 phase.
  • What occurs during the S phase of interphase?
    DNA is replicated, producing identical sister chromatids attached at the centromere. Kinetochore proteins form at centromeres.
  • Describe the G2 phase of interphase.
    Lasts 4-6 hours. Final growth and metabolism phase before mitosis. Enzymes and proteins for cell division are produced.
  • What are the four phases of mitosis?
    1. Prophase 2. Metaphase 3. Anaphase 4. Telophase
  • What key events occur during prophase?
    Chromatin condenses into chromosomes, nuclear membrane and nucleoli disappear, centrosomes move to poles, spindle apparatus forms.
  • What happens during metaphase?
    Chromosomes line up at the cell equator (metaphase plate) with sister chromatids attached to spindle microtubules.
  • Describe anaphase in mitosis.
    Sister chromatids separate at kinetochores and move to opposite poles. Cytokinesis begins.
  • What occurs during telophase?
    Spindle disassembles, chromosomes uncoil, nuclear membrane and nucleoli reappear, cytokinesis completes, forming two identical daughter cells.
  • What is meiosis and where does it occur?
    Meiosis is a reduction division producing haploid gametes (sperm and egg) from diploid cells. It occurs only in sex cells.
  • What are the two divisions of meiosis?
    Meiosis I separates homologous pairs (diploid to haploid). Meiosis II separates sister chromatids, producing 4 haploid gametes.
  • What is synapsis and crossing over in meiosis I prophase?
    Synapsis is pairing of homologous chromosomes forming tetrads. Crossing over is exchange of genetic material between sister chromatids.
  • What happens during metaphase I of meiosis?
    Tetrads line up at the metaphase plate. Sister chromatids remain attached at centromeres.
  • Describe anaphase I of meiosis.
    Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached.
  • What is the outcome of telophase I and cytokinesis?
    Two haploid daughter cells form, each with sister chromatids still attached.
  • How does meiosis II differ from mitosis?
    Meiosis II occurs in haploid cells and separates sister chromatids, producing 4 haploid gametes.
  • What is fertilization?
    Fusion of haploid sperm and egg to form a diploid zygote, restoring the diploid chromosome number.
  • What is cleavage in early embryonic development?
    Rapid mitotic divisions of the zygote producing smaller cells called blastomeres, forming a solid morula.
  • What is a blastocyst?
    A fluid-filled structure formed about 5 days post-fertilization, containing trophoblast cells and an embryoblast.
  • What is implantation?
    Attachment of the blastocyst to the uterine endometrium, occurring 5-7 days after fertilization.
  • What are the three germ layers formed from the epiblast?
    Ectoderm (nervous system, skin epidermis), mesoderm (muscle, bone, blood vessels, dermis), endoderm (epithelial linings of tracts and glands).
  • What are the embryonic membranes and their origins?
    Amnion (from epiblast), yolk sac (from hypoblast), chorion (from trophoblast), allantois (from yolk sac).
  • What is the fetal period?
    From week 9 to 40, characterized by growth and maturation of organs.