Chromosomal Abnormalities

Question 1

What is cytogenetics?

Answer 1

Analysing gross changes in chromosomes

Question 2

What is molecular genetics?

Answer 2

Analysing DNA sequences

Question 3

How are chromosomes processed for karyotyping?

Answer 3

• cell sample added to culture medium with PSA
• incubated at 37 degrees for 48-72 hours
• colcemid added
• hypotonic solution added
• cells are fixed and spread onto a slide
• cells treated with trypsin then stained with Giemsa

Question 4

What does colcemid do? (Karyotyping preparation)

Answer 4

Prevents spindle formation, stopping metaphase.

Question 5

Why are cells treated with trypsin before Giemsa staining?

Answer 5

To partially digest the chromosomes.

Question 6

What are the p and q arms of a chromosome?

Answer 6

P - short arm

Q - long arm

Question 7

Overall frequency of chromosome abnormalities?

Answer 7

1 in 200

Question 8

Frequency of trisomy 21 (Down’s syndrome)?

Answer 8

1 in 700

Question 9

What is reciprocal translocation?

Answer 9

A balanced exchange of material between two chromosomes.

Question 10

What is Robertsonian translocation?

Answer 10

When two chromosomes join together.

Question 11

What is FISH?

Answer 11

Fluorescence in situ hybridisation.

DNA probes labelled with fluorophores are hybridised onto the chromosome preparation or interphase nuclei.

Question 12

What is the purpose of FISH?

Answer 12

• count chromosomes in interphase nuclei
• look for submicroscopic deletions using locus specific probes
• interpret abnormalities more clearly
• look for specific rearrangements such as gene fusions in acquired (not congenital) abnormalities

Question 13

What are microarrays? What is their function?

Answer 13

• new technology with greater resolution for the detection of chromosome abnormalities

Question 14

What are features of a constitutional abnormality?

Answer 14

• occurs at gametogenesis
• affects all cells of the body
• heritable

Question 15

What are features of an acquired abnormality?

Answer 15

• changes occur during lifetime
• affects malignant tissue only
• not heritable

Question 16

What is the role of cytogenetics?

Answer 16

• confirmation of malignancy
• classification of a disease type
• prognosis
• monitoring

Question 17

What is a fusion/hybrid gene?

Answer 17

Fusion of two genes creates a hybrid, which produces a hybrid protein.

Question 18

What is deregulation of a gene?

Answer 18

Occurs when a gene is juxtaposed to a regulating gene (moved next to).
Altered regulation can lead to increased transcription and neoplastic growth.