Part 8 — Higher-order Case-based & Analytical NEET MCQs (Q176–200)

Q176.

A scientist cultures cells with DNA-damaging agents. Cells lacking functional p53 continue dividing. What outcome is expected?
A. Cell cycle arrest in G1
B. Enhanced apoptosis
C. Accumulation of mutations ✅
D. Increased DNA repair

Explanation:

**A. Arrest requires p53 → absent here.
**B. Apoptosis triggered by p53, absent → less apoptosis.
**C. Correct — unchecked DNA damage accumulates.
**D. DNA repair not efficiently induced.

Q177.

A male has a karyotype of 47, XXY. Which is true?
A. Sterile male with gynecomastia ✅
B. Normal fertility
C. Female phenotype
D. Turner’s syndrome

Explanation:

**A. Correct — Klinefelter’s syndrome.
**B. Fertility impaired.
**C. Male, though feminized features possible.
**D. Turner = XO.

Q178.

If a gamete with 24 chromosomes fuses with a normal gamete, the zygote will be:
A. Haploid
B. Triploid
C. Aneuploid (47 chromosomes) ✅
D. Normal diploid

Explanation:

**A. Haploid = single gamete.
**B. Triploid requires n + 2n.
**C. Correct — zygote has 47 → trisomy.
**D. Not normal (46).

Q179.

Which situation is an example of mosaicism?
A. Mutation in germ cells before fertilization
B. Post-zygotic mutation in somatic cells ✅
C. Extra chromosome in every cell
D. Crossing over in meiosis

Explanation:

**A. Germline mutation → inherited, not mosaic.
**B. Correct — mutations after fertilization affect subset of cells.
**C. Extra chromosome in all cells = full aneuploidy.
**D. Crossing over is normal recombination.

Q180.

Why do nerve cells remain in G0 phase?
A. Lack of DNA
B. Terminal differentiation ✅
C. Continuous apoptosis
D. High telomerase activity

Explanation:

**A. They have DNA.
**B. Correct — neurons differentiate and rarely re-enter cell cycle.
**C. Apoptosis = death, not G0.
**D. Telomerase not relevant.

Q181.

A cell exposed to colchicine is arrested in:
A. G1 phase
B. Metaphase ✅
C. Telophase
D. Cytokinesis

Explanation:

**A. G1 not affected.
**B. Correct — colchicine prevents spindle polymerization → metaphase arrest.
C/D. Later stages blocked indirectly.

Q182.

During anaphase I of meiosis, what separates?
A. Sister chromatids
B. Homologous chromosomes ✅
C. Telomeres
D. Chiasmata

Explanation:

**A. Chromatids separate in anaphase II.
**B. Correct — homologues segregate in anaphase I.
C/D. Structures involved but not what segregates.

Q183.

A cancer cell bypasses the spindle assembly checkpoint. What defect occurs?
A. Chromosomes fail to replicate
B. Aneuploidy due to mis-segregation ✅
C. Telomeres shorten
D. Crossing over decreases

Explanation:

**A. Replication is S phase.
**B. Correct — improper segregation → aneuploidy.
C/D. Not checkpoint functions.

Q184.

Which phase of the cell cycle is absent in early embryonic divisions?
A. G1 and G2 ✅
B. S phase
C. M phase
D. Cytokinesis

Explanation:

**A. Correct — cleavage divisions alternate S and M only.
**B. S required for replication.
**C. M required for division.
**D. Cytokinesis always occurs.

Q185.

Which checkpoint is bypassed if DNA damage persists and yet the cell enters S phase?
A. G1/S ✅
B. G2/M
C. Spindle checkpoint
D. Cytokinesis checkpoint

Explanation:

**A. Correct — damaged DNA incorrectly replicated.
**B. G2/M checks post-replication.
**C. Spindle checks attachment.
**D. Cytokinesis checkpoint not defined.

Q186.

A tumor biopsy shows cells with shortened telomeres undergoing apoptosis. What therapy mimics this effect?
A. Telomerase inhibition ✅
B. CDK overexpression
C. p53 suppression
D. Spindle stabilizers

Explanation:

**A. Correct — telomerase inhibitors limit immortality.
**B. Overexpression increases division.
**C. p53 suppression favors survival.
**D. Spindle stabilizers block mitosis differently.

Q187.

A spermatocyte undergoes nondisjunction in meiosis II. What gametes form?
A. 4 abnormal gametes
B. 2 normal, 1 n+1, 1 n–1 ✅
C. All diploid
D. All haploid

Explanation:

**A. Incorrect — not all abnormal.
**B. Correct — half normal, half abnormal.
**C. Diploid from complete failure, not nondisjunction II.
**D. Not all haploid.

Q188.

What explains why cancer cells divide without growth signals?
A. Overactive Ras oncogene ✅
B. p53 activation
C. Cyclin degradation
D. Telomerase inhibition

Explanation:

**A. Correct — Ras mutation = continuous mitogenic signaling.
**B. p53 suppresses growth.
**C. Cyclin degradation halts cycle.
**D. Telomerase inhibition limits proliferation.

Q189.

A woman with trisomy X (47, XXX) is most likely to be:
A. Sterile and severely abnormal
B. Normal female, possibly taller ✅
C. Male phenotype
D. Turner’s syndrome

Explanation:

**A. Severe abnormality uncommon.
**B. Correct — usually phenotypically normal, sometimes taller.
**C. Male requires Y.
**D. Turner = XO.

Q190.

Which is true for meiosis but not for mitosis?
A. Chromosome condensation
B. Nuclear envelope breakdown
C. Crossing over ✅
D. Cytokinesis

Explanation:

A/B/D: Occur in both.
**C. Correct — unique to meiosis I.

Q191.

If APC/C fails to activate separase, cells will arrest in:
A. Prophase
B. Metaphase ✅
C. Telophase
D. Cytokinesis

Explanation:

**A. Prophase = condensation.
**B. Correct — chromatids remain joined, cannot enter anaphase.
C/D. Later stages blocked.

Q192.

A 2n=16 plant undergoes meiosis. After fertilization, the zygote has:
A. 8 chromosomes
B. 16 chromosomes ✅
C. 24 chromosomes
D. 32 chromosomes

Explanation:

**A. Haploid gametes only.
**B. Correct — gametes n=8 → zygote = 16.
**C. 24 = triploid.
**D. 32 = tetraploid.

Q193.

Which event causes aneuploid gametes?
A. Nondisjunction ✅
B. Crossing over
C. Cytokinesis
D. Telomerase activity

Explanation:

**A. Correct — segregation errors → n+1 or n–1 gametes.
**B. Crossing over creates variation, not aneuploidy.
**C. Cytokinesis divides cytoplasm.
**D. Telomerase not involved.

Q194.

Which therapy targets BCR-ABL fusion protein in leukemia?
A. Imatinib ✅
B. Taxol
C. Colchicine
D. Vincristine

Explanation:

**A. Correct — Imatinib inhibits abnormal tyrosine kinase.
B–D. Affect microtubules, not BCR-ABL.

Q195.

Which process restores diploidy after meiosis halves chromosome number?
A. Cytokinesis
B. Fertilization ✅
C. Crossing over
D. DNA replication

Explanation:

**A. Cytokinesis divides cytoplasm.
**B. Correct — fertilization combines gametes restoring 2n.
**C. Crossing over = variation.
**D. Replication duplicates DNA, not sets.

Q196.

Which protein prevents re-replication of DNA in S phase?
A. Cohesin
B. Geminin ✅
C. Telomerase
D. Separase

Explanation:

**A. Cohesin: chromatid cohesion.
**B. Correct — geminin inhibits licensing of replication origins.
**C. Telomerase: telomere maintenance.
**D. Separase: chromatid separation.

Q197.

Which explains how mitosis differs from meiosis II?
A. Mitosis begins with diploid cells ✅
B. Both separate chromatids
C. Both have spindle fibers
D. Both undergo cytokinesis

Explanation:

**A. Correct — mitosis starts diploid, meiosis II starts haploid.
B–D. Common to both.

Q198.

A zygote with 69 chromosomes results from:
A. Monosomy
B. Triploidy ✅
C. Trisomy
D. Tetraploidy

Explanation:

**A. Monosomy = 45.
**B. Correct — 23 × 3 = 69.
**C. Trisomy = 47.
**D. Tetraploid = 92.

Q199.

Which ensures only one spindle attaches to each kinetochore?
A. Rb protein
B. Spindle checkpoint ✅
C. Telomerase
D. Cohesin

Explanation:

**A. Rb regulates G1/S.
**B. Correct — ensures bipolar attachment.
**C. Telomerase lengthens telomeres.
**D. Cohesin holds chromatids, not attachment control.

Q200.

Which property is common to both mitosis and meiosis?
A. Crossing over
B. Chromosome segregation ✅
C. Reductional division
D. Genetic variability

Explanation:

**A. Crossing over unique to meiosis I.
**B. Correct — both segregate chromosomes to daughter cells.
**C. Reductional division = meiosis I only.
**D. Genetic variability only meiosis.

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Part 8 — Higher-order Case-based & Analytical NEET MCQs (Q176–200)