• A karyotype is a complete set of chromosomes in an individual, seen under a light microscope. Chromosomes are shown in pairs, ordered by size. There are 23 pairs of chromosomes in humans. They have a characteristic banding pattern, revealed by the Giemsa stain that binds to heterochromatin, or tightly packed regions of DNA.
• Chromosomal abnormalities, especially extra or missing copies, are revealed by karyotyping. Examples are Down syndrome (trisomy of chromosome 21), Klinefelter syndrome (XXY), and Turner syndrome (missing X). Large chunks of missing DNA are obvious, as in Cri du chat (cry of the cat), from a truncated short arm on chromosome 5. The name comes from the babies’ distinctive cry, caused by abnormal formation of the larynx. Breaks can occur with certain cancers (e.g., Philadelphia chromosome).
Sock arrangement by Gina Glover; ginaglover.com
Real karyotype: http://goo.gl/1FrRH