Meiosis: Inheritance, variation and evolution: Biology: GCSE (9:1)

• Meiosis


  A type of cell division that results in the formation of gametes, in the form of four non-identical daughter cells

  
• Mitosis


  The process of cell division that results in the formation of two daughter cells that are genetically identical to the parent cell

  
• Stages of meiosis

  Meiosis has two stages of division, where one cell divides into two and then the two cells divide to form a total of four cells

  
• Early stages of meiosis

  Copies of genetic information are made, so in a human cell 46 chromosomes are duplicated

  
• First divisive stage of meiosis

  A human cell that has undergone genetic replication divides to form two daughter cells, each with 46 chromosomes

  
• Second divisive stage of meiosis

  The two daughter cells each containing 46 chromosomes divide to form a total of four daughter cells, each with 23 chromosomes

  
• Products of meiosis

  Four non-identical daughter cells called gametes are produced, each with half the number of chromosomes of the parent cell

  
• Purpose of meiosis


  To shuffle genetic information leading to variation and to produce cells that will combine to make a cell with the correct number of chromosomes

  
• Genetic variation


  Differences in the DNA between individuals due to genetic reshuffling in meiosis, which can result in different displayed characteristics

  
• Genetic reshuffling


  Genetic information is swapped between chromosome pairs during meiosis, resulting in gametes with variation

  
• 23 chromosomes


  Gametes have this number of chromosomes so that when they combine during fertilisation, the original number of chromosomes is restored

  
• 46 chromosomes


  The original number of chromosomes in a typical human body cell

  
• Cell division after fertilisation

  Following the fusion of gametes, a fertilised egg divides by mitosis and begins to rapidly increase in cell number

  
• Zygote


  A fertilised egg

  
• Embryo

  As the zygote divides a number of times it eventually becomes an embryo that can develop cells capable of differentiation

  
• Differentiation


  A process where undifferentiated cells produce or become specialised cells with specific structures and functions

  
• Gametes


  A male or female organism's reproductive cells such as the sperm and egg that are the products of meiosis

  
• Gonads


  The reproductive organs that produce gametes via meiosis, such as the testis or ovary