How to Write a Notation of a Karyotype

Chromosomes are arranged by pairs to be examined in a karyotype.
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A karyotype is the representation of the chromosomes of any type of cell. For humans, the information their chromosomes provide is crucial to learning about the genome and diagnosing genetic diseases. Newly married couples are encouraged to get karyotyped to see if their children may be at a higher risk of inheriting genetic diseases. The results of karyotypes are written in a special notation that, while it may look confusing at first, is actually easy to learn and understand.

    Count the number of pairs of chromosomes in the karyotype, except the sex chromosomes, the last two in the set. Write this number. In a normal human, the number will be 46.

    Determine the sex chromosomes, whether they are "XX" or "XY." If they are "XX," the subject is a female; "XY," the subject is a male. Write this combination next to the number after a comma. In a normal woman, this will look like this "46, XX."

    Note any irregularities in the karyotype. If the karyotype has an extra 21st chromosome, write "47, XX, +21, Trisomy-21," indicating the subject is a woman with 47 chromosomes and the extra chromosome is in the 21st pair. Having three chromosomes in a pair is called "Trisomy." If there is an extra sex chromosome, write 47, then the sex chromosomes; for example, "47, XXX."


    • Consult a doctor or diagnostic manual to learn the names of disorders caused by chromosome irregularities, and write the disorder's name in the notation to make it more complete. For example, because an extra 21st chromosome is the cause of Down's syndrome, write the notation of the karyotype as "47, XY, +21,Trisomy-21, Down's Syndrome."

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