Meiosis
                        Meiosis
      • The form of cell division by which gametes, 
                    cell division           gametes, 
        with half the number of chromosomes, are 
             half               chromosomes, 
        produced.
      • Diploid (2n)        haploid (n)
                        
        Diploid (2n)         haploid (n)
      • Meiosis is sexual reproduction.
        Meiosis    sexual reproduction.
      • Two divisions (meiosis I and meiosis II).
        Two divisions meiosis I        meiosis II
               Fertilization
               Fertilization
  • The fusion of a sperm and egg to form a zygote.
                sperm   egg        zygote
  • A zygote is a fertilized egg
                     sperm
        n=23          n=23
         egg
                                   2n=46
                                  zygote
             Meiosis
             Meiosis
   • Sex cells divide to produce gametes (sperm or 
     Sex cells     gametes(sperm or 
    egg).
     egg)
   • Gametes have half the # of chromosomes.
     Gametes half  chromosomes
   • Occurs only in gonads (testes or ovaries).
     Occurs only in gonads (testes or ovaries).
    Male:  spermatogenesis
    Male:  spermatogenesis
    Female:  oogenesis
    Female:  oogenesis
   • Meiosis is similar to mitosis with some 
     Meiosis   mitosis
    chromosomal differences.
      Spermatogenesis
      Spermatogenesis
                                              n=23
       human
       sex cell                                         sperm
                          n=23                n=23
       2n=46
                                                       haploid (n)
                                             n=23
      diploid (2n)         n=23
                                             n=23
                meiosis I         meiosis II
         Meiosis – mouse testes   
         Meiosis – mouse testes   
            Parent cell
                                               st
                                              1  division
             nd
            2  division
                                               4 gametes