meiosis

• what are gametes produced by?

  meiosis
• meiosis produces cells which have what?


  half the normal number of chromosomes
• describe the stage before meiosis happens?

  before cells divide, It duplicates its genetic info, forming 2 armed chromosomes - 1 arm at each chromosome is an exact copy of the other arm. After replication chromosomes arrange themselves into pairs
• explain what happens in the first division of meiosis.


  chromosome pairs line up in centre of cell
• explain what happens following first division of meiosis.

  pairs are then pulled apart so each new cell only has 1 copy of each chromosome. Some father and some mothers chromosomes go into new cell
• what happens in the second division of meiosis?


  chromosomes line up again in the centre of the cell. The arms of chromosomes are pulled apart
• what happens following the second division of meiosis?


  you then get 4 gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically different from others because chromosomes all get shuffled up during meiosis and each gamete only gets half of them at random.
• what does the cell produced by gamete fusion do?


  replicates itself
• why does mitosis repeat many times?


  to produce lots of new cells in an embryo
• after 2 gametes have fused during fertilisation what then happens?


  new cell divides by mitosis to make a copy of itself
• as the embryo develops, these cells then start to what?

  differentiate into different types of specialised cells that make up a whole new organism.
• what happens after fertilisation?

  new cell divides by mitosis producing a clump of identical cells
• what is a clump of identical cells called?

  an embryo