Meiosis, light micrograph

Light micrograph of cells during metaphase I (left), telophase I (second from left) and telophase II (second from right) of meiosis (gamete formation) and after the final cytokinesis (cell division, right). During meiosis four daughter nuclei are formed from one parent nucleus after two stages of nuclear division. Meiosis occurs only in the sex cells (gametes) of the testes and ovaries. At metaphase (I) pairs of homologous chromosomes line up along the centre of the cell ready to be separated. In telophase (I) two nuclei form around the chromosomes before the cell divides into two. Separation in meiosis II results in two cells with half the usual number of chromosomes. The full complement is restored when two gametes fuse during fertilisation. Silver stain., by DR. JUAN F. GIMENEZ-ABIAN / SCIENCE PHOTO LIBRARY