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Production of a gametes

Production of a gametes

In animals the male gamete is sperm, and in female it is an egg cell (ova). In plants the male gamete is pollen grains, and the female gametes are ovules.

Gametes contain only half the normal amount of chromosomes, so in one gamete in humans it will be 23.

  1. The DNA replicates so there are two identical copies of each chromosomes called chromatids
  2. The DNA condense to form double armed chromosomes, made from two sister chromatids
  3. The chromosomes arrange themselves into homologues pairs, so 1 will match up with 1.
  4. First division the homologues pairs are separated, halving the chromosomes number.
  5. Second division – the pairs of sister chromatids are separated
  6. Four new gametes that are generically different are produced.

 

 

Genetic variation:

  • Crossing over of chromatids is when before the first division of meiosis the homologous pairs of chromosomes come together and pair up, two of the chromatids in each pair twist around each other. The twisted bit breaks off their original chromatid and rejoins onto the other chromatid recombining their genetically material. The point where the chromatids break is called the chiasmata.

 

  • Independent assortment of chromosomes is when the four daughter cells formed from meiosis have completely different combinations of chromosomes.