BIOPHOTO ASSOCIATE / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATE / SCIENCE PHOTO LIBRARY
Human sex chromosomes. Coloured Scanning Electron Microscope (SEM) of human X and Y chromosomes, as found in a male. They are also known as the sex chromosomes because they determine the sex of the individual. Females have two X chromosomes; males have an X and a Y chromosome. The X chromosome (at left) is roughly X-shaped; the Y chromosome (at right) is Y-shaped. There are 23 pairs of chromosomes found in each human cell, but only the sex chromosomes differ so much in appearance. In a normal female one X chromosome becomes inactive and the other controls female development. In the male, the Y chromosome forms the male genital system. Magnification: x10,200 at 6x7cm size. Magnification: x35,000 at 8x10 inch size.
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