3

• Somatic cells


  All body cells except the sex cells
• Sex cells

  The gametes, the sperm cell of the male and the egg cell of the female
• Sex cells

  Undergo mitosis and meiosis
• Jacques Monod: '"The fundamental biological variant is DNA"'
• Cell cycle


  • Means for the continuity of life
• Cell cycle

  1. Interphase

  2. Mitotic phase
• Interphase


  The longest phase of the cell cycle process, also known as the resting phase
• Interphase sub-stages

  • G1 phase
  • S-phase
  • G2 phase
• 1. phase

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Meiosis

  The process that produces haploid gametes, reduces the number of chromosomes by half
• Prophase I of meiosis

  1. Leptotene: chromosomes appear as threadlike structures

  2. Zygotene: homologous chromosomes pair up to form bivalent

  3. Pachytene: each homologue chromosome splits into two chromatids, crossing over occurs

  4. Diplotene: chromatids start to divide and separate, connected by DNA strands at points of exchange

  5. Diakinesis: nucleolus disappears, chromosomes coil tightly, centrosomes reach the poles, crossing over has occurred
• Crossing over

  1. Synapsis: homologous chromosomes pair up

  2. Duplication: bivalent chromosomes split longitudinally into four chromatids (tetrad)

  3. Crossing over: paternal and maternal chromatids exchange genetic material at chiasmata

  4. Terminalisation: chiasmata move towards the ends of the chromosomes
• Taxonomic categories

  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum
  • Kingdom
• Binomial names

  • Homo sapiens (Human)
  • Helianthus annuus (Sunflower)
  • Panthera tigris (Tiger)
  • Mangifera indica (Mango)
  • Canis lupus familiaris (Dog)