BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Composite Scanning Electron Micrograph (SEM) of human chromosomes, showing one X and two Y chromosomes, or XYY Syndrome. This is a genetic abnormality in which there is at least one extra Y chromosome to a standard human male karyotype, but unlike the effects are not as pronounced as in other sex chromosome abnormalities (such as Klinefelter syndrome and Turner syndrome). Affected individuals are slightly taller and may have learning disabilities.
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