JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Foetal X and Y chromosomes. Fluorescence in situ hybridization (FISH) micrograph of the cell nuclei of a foetus, showing sex chromosomes. The rounded structures are nuclei; X and Y "sex" chromosomes are seen fluorescing light blue and pink in each nucleus. The presence of an X and Y chromosome establishes this foetus as male; a female foetus would have two X chromosomes. The FISH technique enables chromosomes to be tagged with fluorescent dyes to highlight genetic traits. Apart from determining foetal sex, sex chromosome defects such as in Turner's syndrome (X chromosome only) or Klinefelter's syndrome (XXY chromosomes) can be detected. Photographed at Cytocell Ltd., England.
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