meiosis

• gametes are produced by meiosis. two cell divisions, happens in the reproductive organs
• meiosis produces cells which have half the normal number of chromosomes.
• 1. before the cell starts to divide, it duplicates its genetic information, forming two armed chromosomes, one arm of each chromosome is an exact copy of the other. after replication, the chromosomes arrange themselves into pairs.
• 2. in the first division in meiosis the chromosome pairs line up in the centre of the cell
• 3. the pairs are then pulled apart so each new cell only has one copy of each chromosome. some of the fathers and some of the mothers
• 4. in the second division, the chromosomes line up again in the centre of the cell. the arms of the chromosomes are pulled apart.
• 5. you get 4 gametes. each with a single set of chromosomes. each gamete is genetically different and chromosomes get shuffled up during meiosis. each gamete gets half at random
• after the two gametes have fused during fertilisation, the resulting new cell divides by mitosis to make a copy of itself. repeats many times to make lots of new cells in an embryo. they then start to differentiate into different types of specialised cell that make up a whole organism