What must happen before meiosis can begin?

Why during meiosis 1 even after chromosomes are halfed meiosis happen?

• even though chromosome no is halfed during meiosis 1 why it is repeted

• Answer:

  Ok, I think you have a slight misunderstanding here. Meiosis is used to make gemetes that contain half the genomic material so the other have can be provided by the other gamete. Chromosones are generally drawn in X-shapes. Both of these arms or chromotids contain the same genetic material and in MITOSIS split to form two new cells. In effect if you think about it, before mitosis starts, the cell that begins to divide actually has double the normal genetic information. In MEIOSIS, the process begins the same with X-shaped chromosone carrying copies of themselves. This means the cell has double the normal number of chromosone (double diploid). Meiosis 1 splits the homologous X-Shaped chromosones into 2 cells, containing the normal amount of Chromosone (46) except 23 are actually duplicated in each. Meiosis 2 then splits the 2 cells into four containing half the normal amount of chromosone (or haploid). The chromosones split at the centre and are no longer X-shaped. This means that one precursor cell make 4 gametes (although in women only 1 is viable as the others are extruded as polar bodies) I hope this makes sense... it can be difficult to understand!