Chapter 3 (Meiosis and Mitosis)

• Chromosome theory of inheritance


  Describes how the transmission of chromosomes account for Mendelian patterns of inheritance
• The chromosome theory of inheritance dramatically unfolded as a result of three lines of scientific inquiry

  
• Three lines of scientific inquiry

  • Analysis of the transmission of traits from parent to offspring
  • Inquiry into the material basis of heredity
  • Microscopic examination of the processes of mitosis, meiosis and fertilization
• Mendel's plant hybridization studies

  Contributed to the analysis of the transmission of traits from parent to offspring
• Carl Nägeli and August Weismann


  Contributed to the inquiry into the material basis of heredity
• Boveri and Sutton


  Made chief contributions to the microscopic examination of the processes of mitosis, meiosis and fertilization

  
• Fundamental principles of the chromosome theory of inheritance

  • Chromosomes contain the genetic material
  • Chromosomes are replicated and passed from parent to offspring
  • The nuclei of most eukaryotic cells contain chromosomes that are found in homologous pairs, they are diploid
  • During meiosis, each homolog segregates into one of the two daughter nuclei
  • During the formation of gametes, different types of (nonhomologous) chromosomes segregate independently
  • Each parent contributes one set of chromosomes to its offspring

  
• Chromosomes


  Structures within living cells that contain the genetic material

  
• Chromatin


  The DNA-protein complex in eukaryotes
• Bacterial cell


  • Usually a single circular chromosome found in the nucleoid region of the cytoplasm
  • No nucleus
  • Cytoplasm is enclosed by a plasma membrane
  • Outside the membrane is a rigid cell wall

  
• Eukaryotic cell


  • Contains genetic material (DNA)
  • Has two membranes
  • Usually multiple chromosomes
  • Organizes spindle fibers
  • Supports protein synthesis and respiration/ATP synthesis

  
• Ploidy


  The number of copies of each chromosome that each cell has

  
• Ploidy levels


  • Haploid (n) - one copy
  • Diploid (2n) - two copies
  • Triploid (3n) - three copies
• Most higher organisms are diploid
• Chromosome counts


  • Humans - 46 total (23 per set)
  • Dogs - 78 total (39 per set)
  • Fruit fly - 8 total (4 per set)

  
• Biparental inheritance


  For each chromosome pair, one chromosome comes from each parent
• Homologous chromosomes


  The two chromosomes in a homologous pair that are evolutionarily related, nearly identical in size, have the same banding pattern and centromere location, and have the same genes (but not necessarily the same alleles)

  
• Sex chromosomes


  Homologous, but with drastic changes accumulated over time, differ in size and genetic composition, have short regions of homology, and are inherited as a pair

  
• Cytogenetics


  Microscopic examination of chromosomes to detect abnormal chromosome number or structure, and to distinguish between two closely-related species

  
• Somatic cells


  Diploid body cells, other than gametes
• Germ cells


  Haploid gametes (sperm and egg cells)
• Karyotype preparation


  1. Blood sample collection

  2. Treatment with drugs to stimulate cell division and disrupt spindle formation

  3. Centrifugation to concentrate cells

  4. Suspension in hypotonic solution to cause cell swelling

  5. Second centrifugation to concentrate cells

  6. Suspension in fixative, staining, and placement on slide
• Homologous chromosomes behave as homologs in meiosis

  
• Autosomes


  Chromosomes other than the sex chromosomes
• One purpose of cell division is asexual reproduction, and another is to enable multicellularity
• Binary fission


  The means by which some unicellular organisms like bacteria and yeast reproduce asexually
• Interphase


  The metabolically active stage of the cell cycle, including cell growth and differentiation, as well as DNA replication in the S phase

  
• Mitosis


  The partitioning of chromosomes during the cell cycle
• Restriction point


  The point in G1 phase where a cell is committed to the pathway of cell division
• Chromatids


  The two copies of a replicated chromosome, joined at the centromere to form a pair of sister chromatids or a dyad

  
• Walther Flemming coined the term "mitosis" in the 1870s
• Mitosis

  1. Prophase

  2. Prometaphase

  3. Metaphase

  4. Anaphase

  5. Telophase
• Kinetochore microtubules


  Microtubules that attach to the kinetochore, which is bound to the centromere of each individual chromosome

  
• Polar microtubules


  Microtubules that help "push" the poles away from each other
• Aster microtubules


  Microtubules important for positioning the spindle apparatus
• Microtubule Organizing Center (MTOC)


  The site from which microtubules grow
• Kinesins


  Motor proteins that use energy from ATP hydrolysis to move microtubules
• Microtubules are targets for anti-cancer therapies
• Mitosis


  Cell division process that produces two genetically identical daughter cells

  
• Spindle microtubules


  • Aster microtubules - Important for positioning of the spindle apparatus
  • Polar microtubules - Help to "push" the poles away from each other
  • Kinetochore microtubules - Attach to the kinetochore, which is bound to the centromere of each individual chromosome