Module 4

• Cycles and patterns govern living systems
• Cycles in living systems result to patterns which could be cyclical in nature
• From the molecular to cellular, organismic and ecosystem levels, we are all part of the cycles and patterns by which life continues in the struggle for survival
• Cell cycle


  Interphase and M-phase (Division phase)
• Interphase


  • Cell growth and duplication of cellular structures (G1), replication of the genetic material (S), and double checking and repair of duplicated materials (G2)
• Mitosis


  Equational division leading to the production of 2 daughter cells that are genetically identical to the parent cell
• Meiosis


  Reduction division where 4 daughter cells that are genetically different from the parent cell are produced
• The main purpose of mitosis is to increase number of cells for growth and repair of worn out cells
• The main purpose of meiosis is to maintain the chromosome number of an individual as sex cells are produced in preparation for sexual reproduction
• Major reproductive cycles


  • Haplontic (zygotic meiosis)
  • Diplontic (gametic meiosis)
  • Diplohaplontic (sporic meiosis or alternation of generations)

  
• Haplontic life cycle


  Also called as zygotic meiosis, the zygote is the only diploid cell which immediately undergoes meiosis. The resulting haploid cells are called spores
• Diplontic life cycle


  This life cycle is also called gametic meiosis, the organism is in the diploid condition. The only haploid cells are the gametes, gametes

  are produced by meiosis
• Diplohaplontic life cycle


  Also referred to as alternation of generations, both sporophyte and gametophyte are multicellular and fully functioning individuals. The sporophyte is in the diploid condition while the gametophyte is in the haploid state

  
• In reproduction, cycles and patterns are intertwined
• Patterns in Living Systems

  • Leaf arrangement (phyllotaxis)
  • Flying formation in birds
  • Animal with spots
  • Patterns in a shell
  • Patterns in a bacterial colony

  
• Apomixis


  Occurs in some plants. The gamete doubles in chromosome number and becomes the precursor for a new life. Seeds are produced without fertilization
• Parthenogenesis


  An unfertilized egg cell develops into a mature organism
• Hermaphroditism


  An individual has functioning male and female reproductive systems. Sperms and eggs are produced in the same organism, but self-fertilization does not occur commonly

  
• Sex reversal


  Pattern known as sequential hermaphroditism, organisms undergo a distinction as to females and males throughout their lifetime
• Variations in life cycles and developmental patterns are due primarily to the differential expression of genes in specific cells and tissues
• Studies in the fruit fly are being used to explain patterns of gene expression in animals
• Cell Theory - "Cells arise from the division of other pre-existing cells"
• The M-phase or division phase involves nuclear (Mitosis or Meiosis) and cytoplasmic division (cytokinesis).
• Reproductive cycles involve series of events that would lead to the birth of the next generation of organisms.
• Humans have a diploid chromosome number of 2n=46. In the 23 pairs of chromosomes, one half came from the mother and the other half was contributed by the father.
• Sex Reversal

  • Fish
  • Oysters
  • Protandrous species
• Hermaphroditism

  • Earthworm
  • In persons born with such conditions in humans, both reproductive tissues are non-functional.
• Parthenogenesis

  • Male bees
  • Komodo dragon
  • Daphnia
• Mitosis

  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase