sexual reproduction and meiosis#

    Cards (11)

    • gametes
      are the sperm cells in men and the egg cells in women
      in sexual reproduction two gametes fuse together to form a zygote
      this divides and develops into a new organism
      gametes have a haploid number of chromosomes there's only one copy of each chromosome
    • sexual reproduction
      normal body cells have the diploid number of of chromosomes
      meaning each cell contains two of each chromosome (a pair) one from each parent
      the chromosomes that make up each pair are the same size and have the same genes, although they could have different versions of those genes (called alleles) these pairs of matching chromosomes are called homologous chromosomes
    • meiosis
      is a type of cell divisions that happens in the reproductive organs to produce gametes
      cells that divide by meiosis are diploid to start, but the cells that form are haploid - the chromosome number halved
    • meiosis - interphase
      the whole of meiosis begins with interphase
      during interphase, the cell's DNA unravels and replicates to produce double-armed chromosomes called sister chromatids
    • meiosis 1
      meiosis involves two divisions
      after interphase, the cells enter meiosis 1
      it is the reduction phase (it halves the chromosome number)
    • meiosis - prophase 1
      the chromosomes condense, getting shorter and fatter
      homologous chromosomes pair up - number 1 with 1 and etc
      crossing-over occurs
      just like in mitosis, centrioles start moving to opposite ends of the cell, forming the spindle fibres
      the nuclear envelope breaks down
    • meiosis - metaphase 1 

      the homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres
    • meiosis - anaphase 1

      the spindles contract, pulling the pairs apart (one chromosome goes to each end of the cell)
    • meiosis - telophase 1

      a nuclear envelope forms around each group of chromosomes
      cytokinesis occurs and two haploid daughter cells are produced
    • meiosis 2
      the two daughter cells go through prophase 2, metaphase 2, anaphase 2, telophase 2 (and cytokinesis)
      pretty much the same as the stages in meiosis 1, except with half the number of chromosomes
      in anaphase 2 the sister chromatids are separated
      each new daughter cell inherits one chromatid from each chromosomes
      four haploid daughter cells are produced
    • genetic variation - meiosis 

      is the differences that exist between individuals' genetic material
      the reason meiosis is important is that it creates genetic variation - it makes gametes that are all genetically different
      then during fertilisation any egg can fuse with any sperm which also creates variation
      means individuals are genetically unique
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