What are some limitations of the karyotype as a test for genetic abnormalities?

Question

What are some limitations of the karyotype as a test for genetic abnormalities?

Answer 1

Karyotypes will only detect large changes in chromosome structure: large deletions and insertions (1000's) of base pairs, translocations, inversions, duplications etc. Things that are diagnosed with karyotyoes include: Downs syndrome (trisomy 21). High Resolution R-Band staining can resolve up to 500 basepairs, however I don't believe this is reliable for diagnostic purposes.

They will not detect single nucleotide changes, deletions, or insertions. The majority of genetic diseases are caused by single (or fewer than 10) base pair changes.