ADRIAN T SUMNER / SCIENCE PHOTO LIBRARY ADRIAN T SUMNER / SCIENCE PHOTO LIBRARY
Meiosis. Coloured scanning electron micrograph (SEM) of chromosomes during anaphase (I) of meiosis (gamete formation). Chromosomes consist of deoxyribonucleic acid (DNA) and proteins. 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 anaphase (I) pairs of homologous chromosomes are separated and pulled to opposite poles of the cell by spindles (not seen). This results in two cells with half the usual number of chromosomes. The full complement is restored when two gametes fuse during fertilisation. Magnification: x4,500 when printed 10 centimetres wide.
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