KATERYNA KON / SCIENCE PHOTO LIBRARY KATERYNA KON / SCIENCE PHOTO LIBRARY
Karyotype showing the arrangement of chromosomes in a male or female with Edward's syndrome (trisomy-18). Edward's syndrome is caused by a chromosomal anomaly: the 18th set having three rather than the normal two chromosomes. In karyotyping, chromosomes are arranged in numbered pairs according to a standard classification. The male set differs from the female in the sex pair (bottom right); a female would have XX rather than XY. A male Edward's karyotype is written: 47,XY,+18, a female - 47, XX,+18. The normal chromosome count is 46, 23 from maternal and 23 from paternal origin. Labelled computer illustration.
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