GEN LAB MIDTERMS

• Genetics is the study of heredity and variation
• Heredity


  The transmission of traits from one generation to the next
• Variation


  The genetic differences between individuals
• Cell Division


  1. Interphase

  2. Mitosis

  3. Meiosis
• Interphase


  • Nucleus is distinct and enclosed by nuclear membrane
  • Organelles are separated by membrane, DNA components are in nucleus
  • Contains nucleoli and chromatin
• G1 Phase


  • Nucleus and cytoplasm enlarge
  • Cell imbibes water
  • Division of organelles and secretory/storage granules
  • Chromatin is stretched
• S Phase


  • Active synthesis of DNA and histones
  • DNA content is doubled
  • Each chromatin is replicated
• G2 Phase


  • Active synthesis of RNA and proteins for chromosome synthesis
  • Mitotic spindles are formed
  • Chromatin fiber is folded to form chromosome
• Mitosis


  • Somatic cell division
  • Increases cell number and replaces worn out tissues
  • Composed of Prophase, Metaphase, Anaphase, Telophase
• Ploidy level


  A complete set of chromosomes
• Genome


  All DNA regardless of ploidy level
• Homologous pair


  Pair or set of corresponding chromosomes
• Prophase


  1. Chromosomes shorten, thicken and become visible

  2. Chromatids are pressed against each other

  3. Nucleoli and nuclear membrane disappear

  4. Spindle fibers radiate
• Metaphase

  1. Chromosomes are maximally condensed

  2. Chromosomes align at equatorial plane

  3. Chromatids separate except at centromere

  4. Spindle fibers attach to kinetochores
• Anaphase


  1. Chromatids are pulled to opposite poles

  2. Centromeres become functionally doubled

  3. Poleward movement of chromosomes
• Telophase


  1. Chromosomes regroup into 2 nuclear regions

  2. Chromosomes uncoil and lengthen

  3. Cytokinesis occurs
• Meiosis


  • Gametic cell division
  • Reduces ploidy level by half and completes through fertilization
• Meiosis I


  Reduction cell division
• Meiosis II


  Equational cell division
• Recombination


  Leads to genetic variability
• Meiosis I: Prophase I


  1. Leptonema

  2. Zygonema

  3. Pachynema

  4. Diplonema

  5. Diakinesis
• Leptonema


  • Chromatin appears as long thin threads
• Zygonema


  • Synapsis or formation of homologous chromosomes begins
  • Chromosomes form bivalents with 4 chromatids
  • Synaptonemal complex is formed

  
• Pachynema


  • Chromosomes are thicker due to further coiling
  • Chromatid breaks and repair occurs, leading to crossing over

  
• Diplonema


  • Synaptonemal complex is no longer functional
  • Homologues start separating except at chiasmata
• Diakinesis


  • Bivalents are maximally condensed
  • Chiasmata are terminalized
  • Nucleolus and nuclear membrane disappear
• Meiosis I: Metaphase I

  1. Bivalents align at equatorial plate

  2. Homologues are on opposite sides of equatorial plate

  3. Spindle fibers attach to kinetochores
• Meiosis I: Anaphase I


  1. Homologous chromosomes separate and move to opposite poles

  2. Each pole has haploid chromosome number
• Meiosis I: Telophase I


  1. Chromosomes regroup and their coiled structure begins to relax

  2. Nucleoli reappear forming 2 haploid daughter cells
• Meiosis II: Prophase II

  Same as mitotic prophase, chromosomes begin to condense

  
• Meiosis II: Metaphase II


  Chromosomes align on equatorial plate, centromeres on top

  
• Meiosis II: Anaphase II

  Sister chromatids separate and move to opposite poles
• Meiosis II: Telophase II

  Chromosomes relax and form nuclei, cytokinesis leads to 4 haploid daughter cells
• Onion root tips or bulb cores are used in the experiment since they are actively dividing
• 70% ethanol removes dirt and kills microorganisms so they are not visible under the microscope
• Acetocarmine stains chromosomes by breaking cellulose and allowing the dye to permeate
• 45% acetic acid destains the excess acetocarmine dye
• Alleles


  Alternative forms of genes
• Genotype


  The combination of alleles of an individual
• Phenotype


  The resulting biochemical, behavioral, morphological, or physiological manifestation