Dark bands in a G-banded karyotype correspond mainly to regions that are:

AT-rich, gene-poor and late-replicating

GC-rich, gene-rich and early-replicating

Nucleolar organiser regions only

Centromeric constitutive heterochromatin

How does an isochromosome, such as i(Xq) in some girls with Turner syndrome, arise?

The centromere divides transversely, not lengthwise

A segment between two breaks in one arm is inverted

Both arms break and their broken ends join together

Two acrocentric chromosomes fuse at the centromere

In the karyotype mos 45,X[8]/46,XX[22], the numbers in square brackets give:

The number of cells with each cell line

The bands at which breaks have occurred

The percentage of cells with each line

The number of cultures that were set up

Cytogenetics

68 Kerala MSc MLT Entrance practice questions on Cytogenetics, 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 · Medium
Dark bands in a G-banded karyotype correspond mainly to regions that are:
1. AGC-rich, gene-rich and early-replicating
2. BAT-rich, gene-poor and late-replicating
3. CNucleolar organiser regions only
4. DCentromeric constitutive heterochromatin
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Answer: B · AT-rich, gene-poor and late-replicating
Trypsin treatment followed by Giemsa gives dark G-positive bands in regions that are AT-rich, relatively poor in genes and late-replicating. The pale bands are GC-rich, gene-rich and replicate early. R-banding reverses this pattern. C-banding stains constitutive heterochromatin, and silver staining marks the nucleolar organiser regions on the acrocentric short arms.
- A: GC-rich, gene-rich, early-replicating regions are the pale G-bands (dark R-bands).
- C: Nucleolar organiser regions are shown by silver (NOR) staining.
- D: Centromeric constitutive heterochromatin is shown by C-banding.
Question 2 · Medium
How does an isochromosome, such as i(Xq) in some girls with Turner syndrome, arise?
1. AA segment between two breaks in one arm is inverted
2. BThe centromere divides transversely, not lengthwise
3. CBoth arms break and their broken ends join together
4. DTwo acrocentric chromosomes fuse at the centromere
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Answer: B · The centromere divides transversely, not lengthwise
In an isochromosome the centromere splits across instead of along the chromosome, so one daughter gets two copies of one arm and no copy of the other. An i(Xq) therefore carries two long arms and no short arm. The loss of Xp genes, including SHOX, explains short stature in these girls, while the extra Xq is largely inactivated. The ISCN form is i(X)(q10).
- A: An inverted segment within one arm is a paracentric inversion.
- C: Joining of the broken ends of both arms forms a ring chromosome.
- D: Fusion of two acrocentric chromosomes is a Robertsonian translocation.
Question 3 · Hard
A 70-year-old man with suspected myelodysplastic syndrome has a bone marrow karyotype. Of 20 metaphases, 2 have lost a chromosome 7, 2 have an extra chromosome 8 and 16 are normal. By the ISCN definition, which abnormality forms a clone?
1. ATrisomy 8 only
2. BMonosomy 7 only
3. CBoth abnormalities
4. DNeither abnormality
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Answer: A · Trisomy 8 only
ISCN defines a clone as at least two cells with the same extra chromosome or the same structural rearrangement, or at least three cells missing the same chromosome. Losses need the higher threshold because a chromosome can be lost artefactually when a metaphase bursts during spreading. The two cells with +8 therefore form a clone, but the two cells with -7 do not. More cells, or interphase FISH for chromosome 7, can show whether the loss is real.
- B: Two cells missing a chromosome fall short of the three needed for a loss.
- C: Only the gain meets the definition; the loss does not.
- D: Two cells with the same extra chromosome do meet the definition of a clone.
Question 4 · Medium
In the karyotype mos 45,X[8]/46,XX[22], the numbers in square brackets give:
1. AThe bands at which breaks have occurred
2. BThe percentage of cells with each line
3. CThe number of cells with each cell line
4. DThe number of cultures that were set up
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Answer: C · The number of cells with each cell line
In ISCN, a number in square brackets after a karyotype is the number of cells (metaphases) found with that cell line. Here 8 of 30 cells are 45,X and 22 are 46,XX, so roughly a quarter of the cells lack an X. The prefix mos marks a mosaic arising in one zygote, while chi marks a chimera from two zygotes. The normal cell line is written last in a constitutional karyotype.
- A: Band positions are written in round brackets after the chromosome number.
- B: Percentages are not written in the karyotype; the cell counts are.
- D: The number of cultures is recorded in the report, not in brackets.
Question 5 · Easy
A newborn boy has clenched fists with overlapping fingers, rocker-bottom feet and a small jaw. What is his karyotype most likely to be?
1. A46,XY,del(5)(p14)
2. B47,XY,+21
3. C47,XY,+13
4. D47,XY,+18
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Answer: D · 47,XY,+18
Clenched fists with overlapping index and fifth fingers, rocker-bottom feet and micrognathia are typical of trisomy 18 (Edwards syndrome). Most cases arise from maternal meiotic non-disjunction, and survival beyond the first year is uncommon. Trisomy 13 (Patau syndrome) more often shows cleft lip and palate, polydactyly and scalp defects. In ISCN, +18 means an extra whole chromosome 18.
- A: 5p deletion (cri-du-chat) shows a cat-like cry and microcephaly.
- B: Trisomy 21 shows hypotonia, flat face and a single palmar crease.
- C: Trisomy 13 typically shows cleft lip and palate, polydactyly and scalp defects.
Question 6 · Medium
The karyotype 46,XY,del(5)(p14) describes a male with:
1. ADuplication of 5p from band 5p14
2. BLoss of 5q from band 5q14 to the tip
3. CLoss of 5p from band 5p14 to the tip
4. DA ring chromosome 5 broken at 5p14
Answer and explanation in LearnFree account
Question 7 · Medium
To count copies of chromosome 18 quickly in uncultured amniotic fluid cells by interphase FISH, the most suitable probe is:
1. AA break-apart rearrangement probe
2. BA centromeric (alpha-satellite) probe
3. CA dual-colour dual-fusion probe
4. DA whole chromosome 18 paint
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Question 8 · Medium
For high-resolution banding, lymphocyte cultures are first blocked with methotrexate or excess thymidine and then released. The purpose is to:
1. AArrest the dividing cells at metaphase ready for harvest
2. BStop bacterial and fungal growth in the culture
3. CCollect many prometaphase cells with long chromosomes
4. DStimulate B lymphocytes as well as T lymphocytes
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Question 9 · Medium
Interphase FISH with a break-apart probe for a gene shows, in most tumour nuclei, one fused yellow signal plus one separate red and one separate green signal. This pattern indicates:
1. ATwo normal copies of the gene
2. BDeletion of both copies of the gene
3. CRearrangement of one copy of the gene
4. DAmplification of the gene region
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Question 10 · Hard
A 9-year-old girl with short stature has a blood karyotype of 45,X[26]/46,X,+mar[4]. The small marker chromosome cannot be identified by G-banding. The most important next test is:
1. ABuccal smear for Barr bodies
2. BRepeat the karyotype on skin fibroblasts
3. CExtend the count to 100 metaphases
4. DFISH with X and Y centromere probes
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Question 11 · Medium
A healthy 30-year-old woman who has had three first-trimester miscarriages has the karyotype 45,XX,der(13;14)(q10;q10). This shows:
1. ATurner syndrome with loss of one X chromosome
2. BA balanced Robertsonian translocation carrier
3. CAn unbalanced translocation with trisomy 14
4. DMonosomy 13 with a second, viable cell line
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Question 12 · Easy
For about how long is a standard PHA-stimulated peripheral blood culture for constitutional karyotyping incubated at 37 °C?
1. A72 hours
2. B7 days
3. C21 days
4. D24 hours
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Question 13 · Hard
Amniotic fluid from a 36-year-old woman is cultured by the in situ coverslip method. Of 15 colonies analysed from two independent cultures, one colony on one coverslip has trisomy 2 in all its cells; every other colony is 46,XY. This is best interpreted as:
1. ATrue fetal mosaicism for trisomy 2
2. BPseudomosaicism, most likely a culture artefact
3. CNon-disjunction at maternal meiosis I
4. DMaternal cell contamination of the sample
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Question 14 · Easy
In a chromosome, what structure is formed when DNA is wound around cores of eight histone proteins?
1. AKinetochores
2. BCentromeres
3. CNucleosomes
4. DTelomeres
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Question 15 · Hard
For a patient with suspected CML, interphase FISH with a BCR::ABL1 dual-fusion probe is scored by two technologists, each counting 200 nuclei. One finds 14 nuclei with the abnormal fusion pattern and the other finds 18. The laboratory's normal cut-off is 1.5%. The result is:
1. A8.0%, above the cut-off
2. B16%, above the cut-off
3. C7.0%, above the cut-off
4. D0.08%, below the cut-off
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Question 16 · Easy
At what stage of pregnancy is amniocentesis for fetal chromosome analysis usually performed?
1. A30 to 34 weeks of gestation
2. B15 to 20 weeks of gestation
3. C6 to 8 weeks of gestation
4. D10 to 13 weeks of gestation
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Question 17 · Medium
Before DNA testing became standard, the fragile site at Xq27.3 in fragile X syndrome was shown by culturing lymphocytes in:
1. AA medium with extra fetal calf serum
2. BA medium with added bromodeoxyuridine
3. CA medium with added pokeweed mitogen
4. DA folate-deficient medium
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Question 18 · Medium
A 28-year-old man with normal male genitalia, small testes and azoospermia has a 46,XX karyotype. Which test will most likely explain his male development?
1. AC-banding for Yq heterochromatin
2. BFISH with an SRY probe
3. CBuccal smear for Barr bodies
4. DDNA test for fragile X repeats
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Question 19 · Hard
A 7-year-old boy has pancytopenia, short stature, café-au-lait spots and an absent left thumb. Which cytogenetic test best confirms the suspected diagnosis?
1. ABone marrow karyotype for monosomy 7
2. BInterphase FISH for BCR::ABL1 fusion
3. CSister chromatid exchange with BrdU
4. DBreakage test with diepoxybutane (DEB)
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Question 20 · Hard
A lymphocyte culture has a good mitotic index, but the metaphases are poorly spread, with overlapping fuzzy chromosomes in a grey cytoplasmic background. Colcemid and hypotonic times followed the protocol. The 3:1 methanol-acetic acid fixative was mixed last week and stored. The best corrective step is to:
1. AIncrease the colcemid exposure time to two hours
2. BIncrease the trypsin time before banding
3. CAdd more PHA to the culture medium
4. DUse fixative freshly mixed on the day of harvest
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Question 21 · Medium
A healthy donor's G-banded karyotype shows an enlarged heterochromatin block next to the centromere of one chromosome 9, written 9qh+. This finding is usually:
1. AEvidence of a hidden balanced translocation
2. BA normal inherited variant without clinical effect
3. CAn acquired change pointing to early leukaemia
4. DA partial trisomy 9 needing prenatal diagnosis
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Question 22 · Medium
Most cases of free trisomy 21 arise from nondisjunction during:
1. AMitosis of the early embryo
2. BMaternal meiosis I
3. CMaternal meiosis II
4. DPaternal meiosis I
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Question 23 · Easy
Q-banding stains metaphase chromosomes with:
1. AAcridine orange
2. BGiemsa after trypsin
3. CSilver nitrate
4. DQuinacrine
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Question 24 · Easy
A cell whose chromosome number is not an exact multiple of the haploid number 23, such as 45 or 47, is described as:
1. AEuploid
2. BPolyploid
3. CHaploid
4. DAneuploid
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Question 25 · Easy
In fluorescence in situ hybridisation, chromosomes and nuclei are usually counterstained blue with:
1. AHaematoxylin
2. BLeishman stain
3. CGiemsa
4. DDAPI
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43 more Cytogenetics questions

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Cytogenetics

Dark bands in a G-banded karyotype correspond mainly to regions that are:

How does an isochromosome, such as i(Xq) in some girls with Turner syndrome, arise?

A 70-year-old man with suspected myelodysplastic syndrome has a bone marrow karyotype. Of 20 metaphases, 2 have lost a chromosome 7, 2 have an extra chromosome 8 and 16 are normal. By the ISCN definition, which abnormality forms a clone?

In the karyotype mos 45,X[8]/46,XX[22], the numbers in square brackets give:

A newborn boy has clenched fists with overlapping fingers, rocker-bottom feet and a small jaw. What is his karyotype most likely to be?

The karyotype 46,XY,del(5)(p14) describes a male with:

To count copies of chromosome 18 quickly in uncultured amniotic fluid cells by interphase FISH, the most suitable probe is:

For high-resolution banding, lymphocyte cultures are first blocked with methotrexate or excess thymidine and then released. The purpose is to:

Interphase FISH with a break-apart probe for a gene shows, in most tumour nuclei, one fused yellow signal plus one separate red and one separate green signal. This pattern indicates:

A 9-year-old girl with short stature has a blood karyotype of 45,X[26]/46,X,+mar[4]. The small marker chromosome cannot be identified by G-banding. The most important next test is:

A healthy 30-year-old woman who has had three first-trimester miscarriages has the karyotype 45,XX,der(13;14)(q10;q10). This shows:

For about how long is a standard PHA-stimulated peripheral blood culture for constitutional karyotyping incubated at 37 °C?

Amniotic fluid from a 36-year-old woman is cultured by the in situ coverslip method. Of 15 colonies analysed from two independent cultures, one colony on one coverslip has trisomy 2 in all its cells; every other colony is 46,XY. This is best interpreted as:

In a chromosome, what structure is formed when DNA is wound around cores of eight histone proteins?

For a patient with suspected CML, interphase FISH with a BCR::ABL1 dual-fusion probe is scored by two technologists, each counting 200 nuclei. One finds 14 nuclei with the abnormal fusion pattern and the other finds 18. The laboratory's normal cut-off is 1.5%. The result is:

At what stage of pregnancy is amniocentesis for fetal chromosome analysis usually performed?

Before DNA testing became standard, the fragile site at Xq27.3 in fragile X syndrome was shown by culturing lymphocytes in:

A 28-year-old man with normal male genitalia, small testes and azoospermia has a 46,XX karyotype. Which test will most likely explain his male development?

A 7-year-old boy has pancytopenia, short stature, café-au-lait spots and an absent left thumb. Which cytogenetic test best confirms the suspected diagnosis?

A healthy donor's G-banded karyotype shows an enlarged heterochromatin block next to the centromere of one chromosome 9, written 9qh+. This finding is usually:

Most cases of free trisomy 21 arise from nondisjunction during:

Q-banding stains metaphase chromosomes with:

A cell whose chromosome number is not an exact multiple of the haploid number 23, such as 45 or 47, is described as:

In fluorescence in situ hybridisation, chromosomes and nuclei are usually counterstained blue with: