Meiosis

• Meiosis - a type of nuclear division that gives rise to cells that are genetically different

  • It is used to produce the gametes (sex cells)
• The number of chromosomes must be halved when the gametes (sex cells) are formed

  • otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)
• Reduction division - the chromosome number is halved from diploid to haploid, resulting in genetically different cells

  • the halving of gametes occurs during meiosis
• Reduction division process

  • Starts with chromosomes doubling themselves as in mitosis and lining up in the centre of the cell
  • After this, the cells divide twice so that only one copy of each chromosome passes to each gamete
  • Because of this double division, meiosis produces four haploid cells
• Gametes are haploid - having half the normal number of chromosomes
• Meiosis Process:

  • Each chromosome makes identical copies of itself (forming X-shaped chromosomes)
  • First division - chromosomes pair up along the centre of the cell, recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair
  • Second division - chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)
  • A total of four haploid daughter cells will be produced
• Meiosis process

  A) nucleus

  B) chromosomes

  C) nuclear membrane

  D) replicated

  E) chromosome

  F) duplicated

  G) nuclear membrane

  H) breaks

  I) pair

  J) centre

  K) pairs

  L) separate

  M) opposite sides

  N) dna

  O) swapped

  P) sections

  Q) different combinations

  R) different

  S) organise

  T) one

  U) two

  V) four haploid

  W) daughter

  
• Importance of meiosis:

  • Production of gametes e.g. sperm cells and egg cells, pollen grains and ovum
  • Increases genetic variation of offspring
  • Meiosis produces variation by forming new combinations of maternal and paternal chromosomes
  • every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others
• Differences between meiosis and mitosis (Questions often ask for differences between mitosis and meiosis, learn two or three and remember to BE SPECIFIC when giving your answer):

  A) two cells

  B) daughter

  C) diploid

  D) genetically

  E) identical

  F) parent

  G) one

  H) four

  I) daughter

  J) haploid

  K) genetically

  L) different

  M) parent

  N) two

  
• Process of Meiosis

  A) doubled

  B) diploid

  C) random assortment of chromosomes

  D) cells are different and haploid

  
• Meiosis - cell division where the daughter cells have half the genetic material of the parent cell

  • pairing up of chromosomes on the sides
  • produces cell with half the amount
• The name of the cell formed when the nuclei of two gametes join together is...


  zygote