The Process of Meiosis

Meiosis involves two nuclear divisions: Meiosis I and Meiosis II. They normally occur in succession.In prophase 1, the nuclear membrane disintegrates, the nucleolus disappears and the chromosomes shorten and thicken and become visible. Homologous chromosomes pair up in a process called synapsis. The chromatids of homologous chromosome overlap and exchange genetic material in a process called crossing over. The points at which they cross over are called chiasmata.By Metaphase 1, the centrioles have migrated to the poles and the nuclear spindle has formed. The chromosomes line up on the equator attached to the spindle by their centromeres.During Anaphase 1, the spindle fibres contract pulling each chromosome centromere-first to the poles.The nuclear membrane reforms during telophase 1 and the cytoplasm divides forming two daughter cells.This is followed by Meiosis II in which the two daughter cells divide again, in a division similar to mitosis, to form four genetically different haploid daughter cells.