In the male and female in all animals (and plants) that reproduce sexually to form an embryo, these very first cells form by meiosis.
Meiosis a reductive form of cell division that only occurs in the egg (oocyte) and sperm (spermatozoa) and allows new genetic combinations of offspring to be generated.
Meiosis has 2 key components:
- Genetic reorganisation - the genetic material (chromosomes) that you have from your mother and father are recombined.
- Genetic reductive - the chromosome number is halved and only fertilisation will allow the paired chromosomes that we all contain in all our cells.
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<html5media height="200" width="300">File:Oocyte_Meiosis_01.mp4</html5media>
This movie shows the egg (oocyte) completing the first part of meiosis (meiosis I). The chromosomes are coloured blue, the cell membrane is green. The small structure on the left are chromosomes that will not be used in the embryo.
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