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• Meiosis


  The process where one diploid germ cells divides in order to create either 1 or 4 haploid cells (23 chromosomes)
• Gametogenesis


  Formation of Gametes (Eggs & Sperm)
• Haploid (n)


  • Diploid (2n)
  • Egg (n)
  • Haploid gametes (n = 23)
  • Sperm (n)
  • Ovary
  • Testis
  • Mitosis and development
  • Diploid zygote (2n = 46)
  • Multicellular diploid adults (2n = 46)
• Meiosis is preceded by interphase which includes chromosome replication
• Meiosis has two meiotic divisions
• Meiosis I and Meiosis II

  Called Reduction-division
• The original cell is diploid (2n)
• Four daughter cells produced are haploid / monoploid (1n)
• Daughter cells contain half the number of chromosomes as the original cell
• Meiosis produces gametes (eggs & sperm)
• Meiosis occurs in the testes in males (Spermatogenesis)
• Meiosis occurs in the ovaries in females (Oogenesis)
• Why Do we Need Meiosis?

  • It is the fundamental basis of sexual reproduction
  • Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote
• Replication of Chromosomes


  • Replication is the process of duplicating a chromosome
  • Occurs prior to division
  • Replicated copies are called sister chromatids
  • Held together at centromere
• Replication occurs in Interphase
• Gametogenesis


  Oogenesis or Spermatogenesis
• Spermatogenesis


  • Occurs in the testes
  • Two divisions produce 4 spermatids
  • Spermatids mature into sperm
  • Men produce about 250,000,000 sperm per day
• Teratozoospermia


  • Abnormal sperm morphology
  • Any deviation from the normal size and shape of the sperms
  • Sperm morphology refers to the size and shape of the sperm
  • Under the microscope at least 4-5% of sperms should appear normal
  • Teratozoospermia is diagnosed when more than 95% of sperms in a man's semen sample is of abnormal morphology
  • Toxins, infections and varicoceles contribute to abnormal sperm morphology
• Normal appearing sperm


  • Has an oval elongated head with the dark staining nucleus (DNA) and 1 or 2 empty spaces (vacuoles)
  • The head is connected to the tail by a mid-piece which has a neck
• Morphological Abnormalities


  • The head & tail may be abnormal, they may be giants, dwarfs, or joined in head or in tail
  • Lack motility and don't fertilize the egg
• Numerical Abnormalities


  • Oligospermia: few number of sperms in semen
  • Aspermia: no sperms at all in semen
  • Necrospermia: sperms found dead
• Oogenesis


  • Occurs in the ovaries
  • Two divisions produce 3 polar bodies that die and 1 egg
  • Polar bodies die because of unequal division of cytoplasm
  • Immature egg called oocyte, or ootid
  • Starting at puberty, one oocyte matures into an ovum (egg) every 28 days
• A normal baby girl had about 2 million primary oocytes in her ovaries
• By 7 years old about 300,000 remain, her body reabsorbed the rest
• Only about 400 to 500 oocytes will be released during her reproductive years
• Penetration of the sperm induces the secondary oocyte and the first polar body to complete meiosis II
• Oogenesis


  • Oogonium (diploid)
  • Mitosis
  • Primary oocyte (diploid)
  • Meiosis I
  • Secondary oocyte (haploid)
  • Meiosis II (if fertilization occurs)
  • First polar body may divide (haploid)
  • Polar bodies die
  • Ovum (egg)
  • Second polar body (haploid)
  • Mature egg
• Cell Division


  The process by which a parent cell divides into two or more daughter cells
• Cell Division


  • All cells are derived from pre-existing cells
  • New cells are produced for growth and to replace damaged or old cells
  • Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)
• Before a cell becomes too large, it divides, producing 2 daughter cells
• Each daughter cell is an exact replica of the parent cell
• DNA Replication


  DNA must be copied or replicated before cell division so that each new cell will have an identical copy of the DNA
• Chromosomes


  Threadlike structures within the nucleus containing the genetic information (DNA) that is passed from one generation of cells to the next
• Cells of every organism have a specific number of chromosomes (e.g. fruit flies = 8, humans = 46, carrots = 18)
• Chromatin


  Granular material visible within the nucleus; consists of DNA tightly coiled around proteins
• Chromatid


  One of two identical "sister" parts of a duplicated chromosome
• Centromere


  An area where the chromatids are attached to one another
• All eukaryotic cells store genetic information in chromosomes
• Most eukaryotes have between 10 and 50 chromosomes in their body cells
• Human body cells have 46 chromosomes or 23 identical pairs