18.01.03 Chromosome structure and banding Flashcards
What are the two principal groups of chromosome banding techniques?
1) Those that produce thin alternating bands along the chromosome e.g. G, Q and R.
2) Those that stain only a specific region or band of a chromosome. e.g. C, T, NOR, DAPI/DA.
What is the most common method for staining chromosomes in cytogenetics? What are the benefits of this method?
Giemsa staining/G-banding
Provides the basis for ISCN
Resolution 3-5Mb
What are the stages or G-bading? What is the result.
Treating aged metaphase preparations with a protease (trypsin) before Giemsa stain is applied to generate a reproducible banding pattern.
What are the features of G-band dark and G-band light bands?
G-band dark:
1) Heterochroamatin
2) AT-rich
3) Gene-poor
4) Low histone acetylation
5) LINE repeats
G-band light
1) Euchromatin
2) GC-rich
3) Gene-rich
4) High histone acetylation
5) SINEs
What is R banding? What is its potential benefit over G-banding?
Reverse banding achieved by incubating chromosomes with phosphate buffer before adding Giemsa.
Produces the opposite pattern to G-banding. Telomeres are stained more darkly which makes it easier to see if they have been involved in a rearrangement.
What is Q-banding? When might it be useful to use?
Technique used prior to G-banding.
Visualisation with Quinacrine dihydrochloride
Produces a banding pattern when excited by light
Bright regions of fluorescence are AT-rich (including heterochromatic regions 1qh+, 16qh+ etc)
Y-chr is most fluorescent and therefore Q-banding may be useful when confirming presence/rearrangement of Y chr material.
What is C-banding. When might it be useful to use?
Stains constitutive heterochromatin which is permenantly condensed and composed of repetitive DNA, satellite DNA and some non-repetitive DNA.
Located at/near centromeres
Used to confirm polymoprhic variants and the presence of dicentric and pseudodicentric chromsomes and studying marker chromosome composition.
Chromosomes stipped with barium hydroxide. Not as effective in cH+ regions.
What it T/TC banding?
Telomeric banding.
What is Cd staining? When might it be used?
Produces a pair of dots on each centromere (one for each chromatid) believed to represent the kinetochore.
Only active or functional centromeres will stain (C banding will stain both).
Can be used to study Robertsonian translocations, ring chromosomes and marker chromosomes
What is G-11 banding? When might it be used?
Giemsa banding at pH11
Stains pericentric regions of chromosomes
Useful for determining heterochromatin polymorphisms.
What is replication banding? When is it used?
?same as harlequin banding
Used for the detection of SCEs for use in chromosome breakage analysis.
BrdU is a thymidine analogue that is incorporated into chromosomes. BrdU added to chromsome preps then stained with Giemsa. Two rounds of replication - one chromatid contains BrdU (dark)
What are SCEs?
Reciprocal exchange of genetic material from two identical chromatids following their duplication in S phase. Normal cells have 5-8 per mitosis.
What is NOR staining? Why is it used?
aka Silver (nitrate) staining Used to invetigate p-arm variation of acrocentrics. Identified active NORs. Only technique available for staining satellite stalks.
