Cytogenetics

This article deals with cytogenetics.

General

• Large changes (chromosomal).
  • Maximum resolution 3-4 megabase pairs (3-4 million base pairs); may be less - dependent on band density.
• Morphologic data.

Techniques

• ISH = in situ hybridization.
  • FISH = fluorescent in situ hybridization.
  • SISH = silver in situ hybridization.
• Karyotyping.

Karyotyping

What?

• Metaphase nuclei.

How?

• Chromosomes are identified by:
  • Size (chromosome 1 = largest, chromosome 22 = smallest).
  • Position of centromere.
  • Banding pattern - using (special) stains:
    • Several different techniques (stains) are used:
      • Examples: Q-banding (Q=Quinacrine), C-banding (C=constitutive heterchromatin), G-banding (G=Giemsa), R-banding (R=reverse).
        • Q-banding is the standard at UHN.

Image:

• Karyotype (WC).

Notes:

• Quinacrine dye - AT-rich regions brighter than GC-rich regions.

ISH

• Usu. interphase nuclei.

May be prepared from:

• In situ paraffin sections (section 4 micrometers thick).
• Isolated nuclei (section 10 micrometers thick).
• Cytospin.
• Cultured cells.

Probe types

Types:

• Fusion (two colours).
• Breakapart (two colours).
• Deletion/duplication (e.g. trisomy).

Image:

• Bcr-Abl translocation (WC).

See also

• Molecular pathology.
• Chromosomal translocations.