A nondisjunction error in meiosis can leave an egg or sperm with an extra chromosome. That is a trisomy. It can also leave one missing, which is a monosomy. A karyotype is a photo of all the chromosomes, and it shows the problem. Click each classic disorder.
The karyotype clue
This is the chromosome pair that matters. Normal is two copies. These disorders have three, or just one.
Pick a disorder.
Pick a disordertrisomy & monosomy
What it is
Count it out: a trisomy is an extra chromosome, three instead of two. Down syndrome (T21) and Klinefelter (XXY) are trisomies. A monosomy is a missing one. Turner syndrome is the example, with a single X, or "XO".