C - Banding/Q - Banding/NOR Staining

Question 1

C-banding stains the constitutive heterochromatin of which chromosomes?

Answer 1

1, 9, 16, Y

Question 2

What technique is used to identify a small marker?

Answer 2

DAPI/Distamycin A

Question 3

What does the acronym CBG stand for?

Answer 3

C bands by Barium Hydroxide using Giemsa

Question 4

Which one of these techniques would be MOST helpful in identifying that a marker chromosome is bisatellited?

Answer 4

DAPI/Distamycin staining

Question 5

After G-band analysis, a cytogenetic director suspects that chromosome number 1p has a terminal deletion. What banding procedure would be most helpful in deciding if a deletion has occurred?

Answer 5

R-banding

Question 6

Which one of these abnormalities will produce the brightest Q-band signal?

Answer 6

i(Y)q

Question 7

What is the function of Mcllvaine’s buffer in Q-banding?

Answer 7

To control the pH level

Question 8

What are the major clinical applications of C-banding?

Answer 8

1-Identify dicentric chromosomes.
2-Identify centromere region (or centromere region of ring chromosomes).
3-Differentiate active from inactive DNA, especially in marker chromosomes (larger c-band = more inactive DNA).
4-Identify variable regions of chromosomes 1qh, 9qh, 16qh, and Yqh.

Question 9

What is the major clinical application of R-banding?

Answer 9

Studying small deletions or cryptic translocations, which involve the telomeres of chromosomes.

Question 10

After C-banding, the chromosome pattern looks like solid staining. How to improve it?

Answer 10

This is due to undertreatment and the timing should be adjusted/increased.

Question 11

What does QFQ stand for?

Answer 11

Q-banding by fluorescence using quinacrine

Question 12

What is the preferred pH level of Mcllvaine’s buffer?

Answer 12

pH 5.5
Range - 4.5 to 6.0
Increase the pH to 5.5 increases Q band brightness
Decrease the pH to 4.5 increase band contrast

Question 13

What is the Basic procedure for Q-banding?

Answer 13

• The short exposure of a chromosome preparation to a weak, buffered quinacrine solution at an acid pH (Mcllvaine’s buffer, pH 4.5-6.0)
• Wet mounting in the buffer with glycerol to slow quenching and cover with coverslip.
• Excitation by UV exposure to observe with the fluorescent microscope

Question 14

What are the advantages of Q-banding?

Answer 14

• Extremely quick technique; can finish report the same day you harvest
• By software, it can be inverted into G-banding like pattern
• No damage to chromosome morphology and easy removal of stain by fix so easy sequential banding possible

Question 15

What is the clinical application of Q-Banding?

Answer 15

Identifying the Y chromosome polymorphism

Question 16

What are the disadvantages of Q-banding?

Answer 16

• Poorer quality of photography
• Expensive fluorescent microscopes required
• Fluorescence fades very fast
• Slide is not permanent

Question 17

What does RHG stand for?

Answer 17

Reverse banding using heat and Giemsa

Question 18

What is the procedure for R-Banding?

Answer 18

• Incubate slides in hot phosphate solution for 10 to 15 minutes.
• Cool quickly in tap water. Do not dry
• Stain in 2% Giemsa for 10 to 20 minutes.
• Rinse in xylene
• Rinse in tap water. Air dry

Question 19

What are the qualities of Heterochromatin?

Answer 19

• Highly condensed
• At centromeres and telomeres
• Gene poor / repetitious sequences
• Replicated in late S phase

Question 20

What are the qualities of Euchromatin?

Answer 20

• Less condensed
• At chromosome arms
• Gene rich / contains unique sequences
• Replicated throughout S phase

Question 21

What are the two types of heterochromatin?

Answer 21

Constitutive & Facultative

Question 22

What does C-banding do?

Answer 22

Stain the constitutive heterochromatin at the centromere.

Question 23

What are 4 qualities of C-Banding?

Answer 23

1-Gentically inert
2-Late replicating
3-Rich in AT sequences
4- Highly repetitive DNA

Question 24

No C-bands seen; chromosomes appear ghost-like and pale staining?

Answer 24

Overtreatment which extracted even the heterochromatin

Question 25

Some other bands still visible or a solid stain?

Answer 25

Undertreatment

Question 26

What is the most common chromosomal variant in the human race?

Answer 26

Inversion 9

Question 27

What are ribosomal cistrons?

Answer 27

Ribosomal cistrons are clusters of genes(~400), which code for the ribosomes and are responsible for the formation of the nucleolus in interphase cells.

Question 28

What does Ag-NOR stain?

Answer 28

AgNOR-banding, stains only those NOR containing genes which were transcribed during the previous cell cycle.