The correct order of steps in harvesting a lymphocyte culture is:

Colcemid, hypotonic KCl, fixative, slides

Hypotonic KCl, colcemid, fixative, slides

Colcemid, fixative, hypotonic KCl, slides

Fixative, colcemid, hypotonic KCl, slides

Bone marrow for leukaemia karyotyping is set up directly or as a short culture without a mitogen. Why?

Marrow cells divide on their own

Mitogens would kill the blast cells

Marrow contains no dividing cells

Cytogenetics: chromosomes and karyotyping

46 Kerala PSC Lab Technician Gr II practice questions on Cytogenetics: chromosomes and karyotyping, part of Pathology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
Chromosomes 13, 14, 15, 21 and 22 are described as:
1. ASubmetacentric
2. BMetacentric
3. CTelocentric
4. DAcrocentric
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Answer: D · Acrocentric
In acrocentric chromosomes the centromere lies very near one end, so the short arm is tiny. The short arms of 13, 14, 15, 21 and 22 carry satellites on stalks that hold the ribosomal RNA genes (nucleolar organiser regions). These chromosomes are the ones that join in Robertsonian translocations. Metacentric chromosomes such as 1 and 3 have the centromere near the middle.
- A: Submetacentric chromosomes have clearly unequal arms, as in 4 and 5.
- B: Metacentric chromosomes have the centromere near the middle, as in 1 and 3.
- C: Telocentric chromosomes have the centromere at the very end; none occur in normal humans.
Question 2 · Easy
Which fixative is used in a chromosome harvest?
1. AMethanol-acetic acid (3:1)
2. B95% ethyl alcohol
3. C10% formal saline
4. DBouin's fluid
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Answer: A · Methanol-acetic acid (3:1)
Freshly made methanol and glacial acetic acid (3:1) fixes the swollen cells, removes water and lipid, and hardens the chromosomes. The cells are washed in several changes of fixative before slides are made. Fresh fixative gives good spreading, while old or watery fixative gives poor spreads. Formalin cross-links proteins and is not used, because it spoils both spreading and banding.
- B: Ethanol alone is a cytology smear fixative, not a harvest fixative.
- C: Formalin is a tissue fixative and spoils chromosome spreading and banding.
- D: Bouin's fluid is a picric acid tissue fixative.
Question 3 · Medium
Colchicine (or colcemid) arrests cells in metaphase because it:
1. AHardens the chromosomes
2. BBlocks spindle formation
3. CSwells the cells with water
4. DStimulates cell division
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Answer: B · Blocks spindle formation
Colchicine and its analogue colcemid bind tubulin and stop the mitotic spindle from forming. Without a spindle the chromosomes cannot separate, so dividing cells collect in metaphase, when the chromosomes are condensed and visible. Exposure is kept short, because long exposure makes the chromosomes too short and compact for banding. Division itself is started by a mitogen, not by colchicine.
- A: Fixing and hardening are done by methanol-acetic acid.
- C: Swelling is the effect of the hypotonic solution.
- D: Division is started by a mitogen such as PHA.
Question 4 · Medium
The correct order of steps in harvesting a lymphocyte culture is:
1. AHypotonic KCl, colcemid, fixative, slides
2. BColcemid, fixative, hypotonic KCl, slides
3. CColcemid, hypotonic KCl, fixative, slides
4. DFixative, colcemid, hypotonic KCl, slides
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Answer: C · Colcemid, hypotonic KCl, fixative, slides
Colcemid is added to the living culture first, so that dividing cells collect in metaphase. The cells are then spun down and swollen in hypotonic 0.075 M KCl. Fixative (methanol-acetic acid 3:1) comes next, killing the cells and hardening the chromosomes, and finally the suspension is dropped onto slides. Fixing before the hypotonic step would stop the cells swelling, so the chromosomes would not spread.
- A: Colcemid must act on living, dividing cells before the hypotonic step.
- B: Fixed cells cannot swell, so a hypotonic step after fixation is useless.
- D: Fixation kills the cells, so colcemid added afterwards cannot work.
Question 5 · Medium
Bone marrow for leukaemia karyotyping is set up directly or as a short culture without a mitogen. Why?
1. AMitogens would kill the blast cells
2. BMitogens act only on red cells
3. CMarrow cells divide on their own
4. DMarrow contains no dividing cells
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Answer: C · Marrow cells divide on their own
Bone marrow contains many cells that are already dividing, including the abnormal clone in leukaemia. A direct preparation or a 24-hour unstimulated culture captures these cells in metaphase. Adding PHA would mainly make normal T lymphocytes divide and could hide the abnormal clone. Blood lymphocytes, in contrast, are resting cells and need PHA.
- A: PHA does not kill blasts; it would mainly stimulate normal T cells.
- B: PHA acts on T lymphocytes, not on red cells.
- D: Marrow is rich in dividing cells, which is why no mitogen is needed.
Question 6 · Hard
On a harvested slide, 2,500 cells are counted and 60 of them are in mitosis. The mitotic index is:
1. A24%
2. B2.4%
3. C0.24%
4. D2.5%
Answer and explanation in LearnFree account
Question 7 · Easy
In chromosome structure, telomeres are:
1. AStalks that carry ribosomal RNA genes
2. BThe primary constriction of a chromosome
3. CRepeated DNA caps at chromosome ends
4. DDark bands rich in AT base pairs
Answer and explanation in LearnFree account
Question 8 · Medium
Why are cells treated with 0.075 M potassium chloride during harvesting?
1. ATo arrest the cells in metaphase
2. BTo swell the cells so chromosomes spread
3. CTo fix and harden the chromosomes
4. DTo remove proteins for banding
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Question 9 · Hard
A man is referred for infertility. In a G-banded 20-cell count, 19 cells are 46,XY and one cell has 45 chromosomes, lacking one chromosome 7. This is best reported as:
1. ACulture contamination
2. BA malignant clone
3. CMosaic monosomy 7
4. DA random loss, not a clone
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Question 10 · Medium
Why is blood for chromosome culture collected in sodium heparin and not EDTA?
1. AEDTA clots the sample in transit
2. BHeparin makes T cells divide
3. CHeparin improves chromosome staining
4. DEDTA inhibits lymphocyte growth
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Question 11 · Easy
Which mitogen is added to peripheral blood cultures to make T lymphocytes divide?
1. ATrypsin
2. BColcemid
3. CPhytohaemagglutinin
4. DPotassium chloride
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Question 12 · Hard
A lymphocyte culture gives plenty of metaphases, but the chromosomes are very short and compact, with too few bands to analyse. The most likely cause is:
1. APHA left out of the culture
2. BHypotonic step too short
3. CSlides stained too long
4. DColcemid exposure too long
Answer and explanation in LearnFree account
Question 13 · Easy
In the Denver classification, human chromosomes are sorted into how many groups?
1. ASeven (A to G)
2. BNine (A to I)
3. CTwelve (A to L)
4. DFive (A to E)
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Question 14 · Medium
Chromosomes within each metaphase lie bunched together and overlapping. Which change in slide-making is most likely to improve spreading?
1. AUse a denser cell suspension
2. BMake fixative a day ahead
3. CStain longer with Giemsa
4. DDrop cells onto wet, chilled slides
Answer and explanation in LearnFree account
Question 15 · Hard
Two patient cultures and a normal control culture, all set up on the same day with the same batch of medium and PHA, show no dividing cells at harvest. The most likely cause is:
1. AA faulty reagent or incubator
2. BHypotonic step too short
3. CLymphopenia in both patients
4. DColcemid exposure too long
Answer and explanation in LearnFree account
Question 16 · Easy
What is the primary constriction of a chromosome called?
1. ASecondary constriction
2. BCentromere
3. CTelomere
4. DSatellite stalk
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Question 17 · Hard
A chromosome is 9 µm long, with a short arm of 3 µm and a long arm of 6 µm. Its centromeric index and type are:
1. A67%, submetacentric
2. B33%, acrocentric
3. C33%, submetacentric
4. D50%, metacentric
Answer and explanation in LearnFree account
Question 18 · Medium
In the Denver classification, the X chromosome is placed in which group?
1. AGroup C
2. BGroup A
3. CGroup G
4. DGroup E
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Question 19 · Medium
On a harvested slide, most metaphases have burst, with chromosomes scattered widely and many cells counting under 46. The most likely error is:
1. AColcemid exposure too short
2. BPhytohaemagglutinin omitted
3. CCells left in fixative overnight
4. DHypotonic treatment too long
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Question 20 · Medium
To obtain long prometaphase chromosomes for high-resolution banding, lymphocyte cultures are often synchronised with:
1. APotassium chloride for 1 hour
2. BDouble the usual PHA
3. CMethotrexate, then thymidine
4. DColcemid for 24 hours
Answer and explanation in LearnFree account
Question 21 · Easy
Which culture medium is commonly used for peripheral blood chromosome cultures?
1. ASelenite F broth
2. BSabouraud broth
3. CRPMI 1640
4. DThioglycollate broth
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Question 22 · Easy
For how long are phytohaemagglutinin-stimulated blood cultures for routine karyotyping usually incubated at 37°C?
1. A7 days
2. B24 hours
3. C6 hours
4. D72 hours
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Question 23 · Easy
How many chromosomes are present in a normal human egg or sperm?
1. A22
2. B46
3. C23
4. D44
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Question 24 · Easy
Which letter denotes the short arm of a chromosome?
1. Ac
2. Bp
3. Cq
4. Ds
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Question 25 · Medium
Chronic lymphocytic leukaemia is usually a B-cell disease. For its karyotype, why is a culture stimulated with phytohaemagglutinin alone a poor choice?
1. APHA arrests cells before metaphase
2. BPHA mainly stimulates T cells
3. CPHA is inactivated by heparin
4. DPHA destroys B cells in culture
Answer and explanation in LearnFree account

21 more Cytogenetics: chromosomes and karyotyping questions

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Cytogenetics: chromosomes and karyotyping

Chromosomes 13, 14, 15, 21 and 22 are described as:

Which fixative is used in a chromosome harvest?

Colchicine (or colcemid) arrests cells in metaphase because it:

The correct order of steps in harvesting a lymphocyte culture is:

Bone marrow for leukaemia karyotyping is set up directly or as a short culture without a mitogen. Why?

On a harvested slide, 2,500 cells are counted and 60 of them are in mitosis. The mitotic index is:

In chromosome structure, telomeres are:

Why are cells treated with 0.075 M potassium chloride during harvesting?

A man is referred for infertility. In a G-banded 20-cell count, 19 cells are 46,XY and one cell has 45 chromosomes, lacking one chromosome 7. This is best reported as:

Why is blood for chromosome culture collected in sodium heparin and not EDTA?

Which mitogen is added to peripheral blood cultures to make T lymphocytes divide?

A lymphocyte culture gives plenty of metaphases, but the chromosomes are very short and compact, with too few bands to analyse. The most likely cause is:

In the Denver classification, human chromosomes are sorted into how many groups?

Chromosomes within each metaphase lie bunched together and overlapping. Which change in slide-making is most likely to improve spreading?

Two patient cultures and a normal control culture, all set up on the same day with the same batch of medium and PHA, show no dividing cells at harvest. The most likely cause is:

What is the primary constriction of a chromosome called?

A chromosome is 9 µm long, with a short arm of 3 µm and a long arm of 6 µm. Its centromeric index and type are:

In the Denver classification, the X chromosome is placed in which group?

On a harvested slide, most metaphases have burst, with chromosomes scattered widely and many cells counting under 46. The most likely error is:

To obtain long prometaphase chromosomes for high-resolution banding, lymphocyte cultures are often synchronised with:

Which culture medium is commonly used for peripheral blood chromosome cultures?

For how long are phytohaemagglutinin-stimulated blood cultures for routine karyotyping usually incubated at 37°C?

How many chromosomes are present in a normal human egg or sperm?

Which letter denotes the short arm of a chromosome?

Chronic lymphocytic leukaemia is usually a B-cell disease. For its karyotype, why is a culture stimulated with phytohaemagglutinin alone a poor choice?