2026 CG Exam Prep: Scientist in Cytogenetics
Practice Questions, Answer Rationales, Chromosome
Analysis, Karyotyping, FISH, Molecular Genetics &
Laboratory Methods Study Guide
Domain 1: Specimen Preparation, Culture, and Harvest (Questions 1–25)
Question 1. Which of the following is the preferred anticoagulant for peripheral
blood specimens collected for routine constitutional cytogenetic analysis?
A) EDTA
B) Sodium heparin
C) Sodium citrate
D) Potassium oxalate
Rationale: Sodium heparin is the preferred anticoagulant for cytogenetic blood
cultures because it does not chelate calcium and magnesium, which are essential
for cell division. EDTA and citrate chelate these ions and inhibit lymphocyte
proliferation.
Question 2. Which specimen type is the gold standard for prenatal cytogenetic
diagnosis?
A) Maternal blood
B) Amniotic fluid
C) Chorionic villus sampling (CVS)
D) Fetal blood
Rationale: Amniotic fluid is the gold standard for prenatal cytogenetic diagnosis,
providing fetal cells for culture and karyotyping. CVS may be used earlier in
pregnancy but has a higher risk of mosaicism confined to the placenta.
Question 3. What is the recommended transport temperature for a peripheral blood
specimen for cytogenetic analysis?
,A) Frozen
B) Room temperature (20–25°C)
C) Refrigerated (2–8°C)
D) Incubated at 37°C
Rationale: Peripheral blood specimens for cytogenetic analysis should be
transported at room temperature. Refrigeration or freezing can reduce cell viability
and mitotic index.
Question 4. What is the primary purpose of using phytohemagglutinin (PHA) in
lymphocyte cultures?
A) Stimulates T-lymphocytes to divide
B) Inhibits cell division
C) Prevents clotting
D) Selects for B-lymphocytes
Rationale: Phytohemagglutinin (PHA) is a mitogen that stimulates T-lymphocytes
to undergo mitosis, allowing chromosome analysis of peripheral blood cultures.
Question 5. Which cell cycle stage is analyzed for routine chromosome analysis?
A) G1 phase
B) S phase
C) G2 phase
D) Metaphase
Rationale: Metaphase chromosomes are most condensed and therefore most
amenable to banding and analysis. Cells are arrested in metaphase using spindle
inhibitors such as colcemid.
Question 6. What is the purpose of colcemid in cytogenetic harvest?
A) Arrests cells in metaphase by inhibiting spindle formation
B) Stimulates cell division
C) Fixes chromosomes
D) Stains chromosomes
,Rationale: Colcemid (demecolcine) inhibits microtubule polymerization,
preventing spindle formation and arresting cells in metaphase where chromosomes
are maximally condensed.
Question 7. What is the purpose of hypotonic solution in cytogenetic harvest?
A) Swelling cells to spread chromosomes
B) Fixing chromosomes
C) Staining chromosomes
D) Arresting cells in metaphase
Rationale: Hypotonic solution (e.g., 0.075 M KCl) causes cells to swell and
chromosomes to spread apart, improving chromosome morphology and reducing
overlap.
Question 8. Which fixative is used in cytogenetic harvest?
A) Formalin
B) Methanol-acetic acid (3:1)
C) Ethanol
D) Glutaraldehyde
Rationale: Methanol-acetic acid (3:1) is the standard fixative for cytogenetic
preparations. It preserves chromosome morphology and removes water from cells.
Question 9. What is the recommended culture time for peripheral blood
lymphocyte cultures for routine constitutional analysis?
A) 24 hours
B) 48–72 hours
C) 5–7 days
D) 10–14 days
Rationale: Peripheral blood lymphocyte cultures are typically incubated for 48–72
hours to allow adequate lymphocyte proliferation and sufficient metaphase cells
for analysis.
, Question 10. Which type of culture is used for bone marrow specimens in
hematologic malignancy analysis?
A) Short-term (24–48 hours) and direct cultures
B) Long-term (5–7 days) only
C) 72-hour PHA-stimulated culture
D) 14-day fibroblast culture
Rationale: Bone marrow specimens for hematologic malignancy analysis are
typically cultured short-term (24–48 hours) or processed directly to capture the
proliferating neoplastic clone, which may not survive longer culture periods.
Question 11. What is the purpose of a "direct" harvest in bone marrow
cytogenetics?
A) To analyze cells without culture, capturing the in vivo proliferating clone
B) To culture cells for 72 hours
C) To stimulate T-cell proliferation
D) To establish a fibroblast cell line
Rationale: Direct harvest processes bone marrow cells without culture, capturing
the in vivo dividing cell population, which may be lost during culture.
Question 12. Which of the following is a sign of poor-quality chromosome
preparations?
A) Excessive cytoplasm and overlapping chromosomes
B) Well-spread chromosomes with minimal overlap
C) Sharp, distinct banding patterns
D) Consistent staining intensity
Rationale: Poor-quality preparations show excessive residual cytoplasm,
chromosome overlap, and fuzzy or indistinct bands. High-quality preparations have
well-spread chromosomes with minimal cytoplasmic background.
Question 13. What is the recommended mitotic index for a good-quality
cytogenetic preparation?
Practice Questions, Answer Rationales, Chromosome
Analysis, Karyotyping, FISH, Molecular Genetics &
Laboratory Methods Study Guide
Domain 1: Specimen Preparation, Culture, and Harvest (Questions 1–25)
Question 1. Which of the following is the preferred anticoagulant for peripheral
blood specimens collected for routine constitutional cytogenetic analysis?
A) EDTA
B) Sodium heparin
C) Sodium citrate
D) Potassium oxalate
Rationale: Sodium heparin is the preferred anticoagulant for cytogenetic blood
cultures because it does not chelate calcium and magnesium, which are essential
for cell division. EDTA and citrate chelate these ions and inhibit lymphocyte
proliferation.
Question 2. Which specimen type is the gold standard for prenatal cytogenetic
diagnosis?
A) Maternal blood
B) Amniotic fluid
C) Chorionic villus sampling (CVS)
D) Fetal blood
Rationale: Amniotic fluid is the gold standard for prenatal cytogenetic diagnosis,
providing fetal cells for culture and karyotyping. CVS may be used earlier in
pregnancy but has a higher risk of mosaicism confined to the placenta.
Question 3. What is the recommended transport temperature for a peripheral blood
specimen for cytogenetic analysis?
,A) Frozen
B) Room temperature (20–25°C)
C) Refrigerated (2–8°C)
D) Incubated at 37°C
Rationale: Peripheral blood specimens for cytogenetic analysis should be
transported at room temperature. Refrigeration or freezing can reduce cell viability
and mitotic index.
Question 4. What is the primary purpose of using phytohemagglutinin (PHA) in
lymphocyte cultures?
A) Stimulates T-lymphocytes to divide
B) Inhibits cell division
C) Prevents clotting
D) Selects for B-lymphocytes
Rationale: Phytohemagglutinin (PHA) is a mitogen that stimulates T-lymphocytes
to undergo mitosis, allowing chromosome analysis of peripheral blood cultures.
Question 5. Which cell cycle stage is analyzed for routine chromosome analysis?
A) G1 phase
B) S phase
C) G2 phase
D) Metaphase
Rationale: Metaphase chromosomes are most condensed and therefore most
amenable to banding and analysis. Cells are arrested in metaphase using spindle
inhibitors such as colcemid.
Question 6. What is the purpose of colcemid in cytogenetic harvest?
A) Arrests cells in metaphase by inhibiting spindle formation
B) Stimulates cell division
C) Fixes chromosomes
D) Stains chromosomes
,Rationale: Colcemid (demecolcine) inhibits microtubule polymerization,
preventing spindle formation and arresting cells in metaphase where chromosomes
are maximally condensed.
Question 7. What is the purpose of hypotonic solution in cytogenetic harvest?
A) Swelling cells to spread chromosomes
B) Fixing chromosomes
C) Staining chromosomes
D) Arresting cells in metaphase
Rationale: Hypotonic solution (e.g., 0.075 M KCl) causes cells to swell and
chromosomes to spread apart, improving chromosome morphology and reducing
overlap.
Question 8. Which fixative is used in cytogenetic harvest?
A) Formalin
B) Methanol-acetic acid (3:1)
C) Ethanol
D) Glutaraldehyde
Rationale: Methanol-acetic acid (3:1) is the standard fixative for cytogenetic
preparations. It preserves chromosome morphology and removes water from cells.
Question 9. What is the recommended culture time for peripheral blood
lymphocyte cultures for routine constitutional analysis?
A) 24 hours
B) 48–72 hours
C) 5–7 days
D) 10–14 days
Rationale: Peripheral blood lymphocyte cultures are typically incubated for 48–72
hours to allow adequate lymphocyte proliferation and sufficient metaphase cells
for analysis.
, Question 10. Which type of culture is used for bone marrow specimens in
hematologic malignancy analysis?
A) Short-term (24–48 hours) and direct cultures
B) Long-term (5–7 days) only
C) 72-hour PHA-stimulated culture
D) 14-day fibroblast culture
Rationale: Bone marrow specimens for hematologic malignancy analysis are
typically cultured short-term (24–48 hours) or processed directly to capture the
proliferating neoplastic clone, which may not survive longer culture periods.
Question 11. What is the purpose of a "direct" harvest in bone marrow
cytogenetics?
A) To analyze cells without culture, capturing the in vivo proliferating clone
B) To culture cells for 72 hours
C) To stimulate T-cell proliferation
D) To establish a fibroblast cell line
Rationale: Direct harvest processes bone marrow cells without culture, capturing
the in vivo dividing cell population, which may be lost during culture.
Question 12. Which of the following is a sign of poor-quality chromosome
preparations?
A) Excessive cytoplasm and overlapping chromosomes
B) Well-spread chromosomes with minimal overlap
C) Sharp, distinct banding patterns
D) Consistent staining intensity
Rationale: Poor-quality preparations show excessive residual cytoplasm,
chromosome overlap, and fuzzy or indistinct bands. High-quality preparations have
well-spread chromosomes with minimal cytoplasmic background.
Question 13. What is the recommended mitotic index for a good-quality
cytogenetic preparation?
