NUMS — Medical & Dental Entry Test

NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 6)

Take the NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 6): 30 multiple-choice questions (40 minutes) with instant scoring and…

What this test covers

30 NUMS Biology

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. In a population at Hardy–Weinberg equilibrium, an autosomal recessive disease affects 1 in 2,500 people. Approximately what fraction of the population are carriers?
- A. about 1.0%
- B. about 2.0%
- C. about 3.9% ✓
- D. about 7.8%
Answer: C. about 3.9%
Explanation: q² = 1/2500, so q = 0.02 and p = 0.98. Carriers = 2pq = 2 × 0.98 × 0.02 ≈ 0.039 (3.9%).
Q2. A population of 1,000 has 400 AA, 400 Aa and 200 aa individuals. What is the frequency of allele A, and is the population in Hardy–Weinberg equilibrium for this locus?
- A. 0.6; no, since heterozygotes number fewer than the 480 expected ✓
- B. 0.4; yes, since q² equals the observed aa frequency of 0.2 here
- C. 0.6; yes, since the genotype counts add up to exactly the 1,000 total
- D. 0.5; no, since there are too few homozygotes
Answer: A. 0.6; no, since heterozygotes number fewer than the 480 expected
Explanation: p = (2×400 + 400)/2000 = 0.6. Expected AA 360, Aa 480, aa 160 differ from observed values, so it is not in equilibrium.
Q3. A test cross of AaBb × aabb gives offspring in the numbers AaBb 42, Aabb 8, aaBb 7, aabb 43. Taking one map unit as 1% recombination, what is the distance between the two genes?
- A. 85 map units
- B. 15 map units ✓
- C. 50 map units
- D. 7.5 map units
Answer: B. 15 map units
Explanation: Recombinants are Aabb and aaBb: (8 + 7)/100 = 15%, so 15 map units.
Q4. Two pairs of genes interact so that the homozygous recessive condition at one locus masks the other, giving an F₂ ratio of 9 : 3 : 4. In an F₂ of 160 offspring, how many are expected in the class with the ratio number 4?
- A. 30
- B. 40 ✓
- C. 10
- D. 90
Answer: B. 40
Explanation: The ratio has 16 parts; 4/16 × 160 = 40.
Q5. Two white-flowered sweet pea lines are crossed and the F₁ is purple. Selfing the F₁ gives a ratio of 9 purple : 7 white. If 320 F₂ plants are grown, how many purple are expected?
- A. 240
- B. 140
- C. 60
- D. 180 ✓
Answer: D. 180
Explanation: 9/16 × 320 = 180 (complementary gene action).

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Q6. A woman with blood group A whose father was group O marries a man with blood group B whose mother was group O. What is the probability that their child is group O?
- A. 1/2
- B. 1/8
- C. 1/4
- D. 0
Q7. An X-linked dominant trait affects a father but not the mother (who is homozygous normal). What is expected among their children?
- A. Half of the sons and half of the daughters are affected
- B. All children are carriers but none are affected
- C. All daughters are affected and no sons are affected
- D. All sons are affected and no daughters are affected
Q8. Two unaffected parents have a child with an autosomal recessive disorder. What is the probability that an unaffected sibling of this child is a carrier?
- A. 2/3
- B. 1/3
- C. 1/4
- D. 1/2
Q9. The frequency of Down syndrome increases with maternal age. One reason is that:
- A. older mothers produce sperm containing extra chromosomes as they age
- B. chromosome 21 mutates in the somatic cells of the older mothers' bodies
- C. oocytes remain arrested in meiosis for decades, risking non-disjunction
- D. older women ovulate several eggs each cycle by repeated mitosis
Q10. A human diploid G₁ nucleus contains 6 pg of DNA. How much DNA does a secondary spermatocyte nucleus contain?
- A. 3 pg
- B. 1.5 pg
- C. 12 pg
- D. 6 pg
Q11. How many chromatids are present in a human cell at metaphase II of meiosis?
- A. 23
- B. 46
- C. 92
- D. 69
Q12. An organism has 2n = 8. Ignoring crossing over, how many different combinations of maternal and paternal chromosomes can its gametes contain?
- A. 8
- B. 64
- C. 16
- D. 4
Q13. At the moment of ovulation, the human oocyte released from the follicle is arrested at:
- A. telophase of meiosis II
- B. prophase of meiosis I
- C. metaphase of meiosis I
- D. metaphase of meiosis II
Q14. In a woman whose luteal phase is a constant 14 days, a cycle lasts 35 days. On roughly which day will ovulation occur?
- A. Day 14
- B. Day 28
- C. Day 17
- D. Day 21
Q15. A combined oral contraceptive pill prevents ovulation mainly because its hormones:
- A. destroy the corpus luteum after fertilisation
- B. keep FSH and LH low by negative feedback
- C. raise LH to a constantly high level
- D. block the passage of sperm in the oviduct
Q16. If hCG were not produced after implantation, what would happen to the pregnancy and why?
- A. It would fail; the corpus luteum would degenerate and progesterone fall
- B. It would continue because oestrogen replaces all other pregnancy hormones
- C. It would fail because FSH would rise too high and trigger new ovulation
- D. It would continue normally because the placenta starts making hCG later on
Q17. A man's sperm cannot release acrosomal enzymes. What is the most likely consequence?
- A. Sperm cannot make testosterone, so no sperm are formed at all
- B. Sperm cannot penetrate the egg coverings, so fertilisation fails
- C. Sperm cannot swim, since acrosomes supply their energy for motility
- D. Eggs are fertilised but the zygote cannot divide
Q18. A plant has 2n = 14. How many chromosomes are in an endosperm cell formed by double fertilisation?
- A. 7
- B. 28
- C. 21
- D. 14
Q19. Compared with insect-pollinated flowers, wind-pollinated flowers usually have:
- A. small stigmas enclosed deep inside the flower, hidden by petals
- B. scented petals, nectar guides and very little sticky pollen
- C. showy bright petals, sweet nectar and sticky heavy pollen
- D. feathery stigmas, small dull petals and much light pollen
Q20. In a Meselson–Stahl type experiment, bacteria grown for many generations in ¹⁵N medium are shifted to ¹⁴N medium. After three generations of replication, what fraction of the DNA molecules are hybrid (¹⁵N/¹⁴N)?
- A. 1/2
- B. 3/4
- C. 1/8
- D. 1/4
Q21. A mutant cell lacks functional DNA ligase. Which result is expected during DNA replication?
- A. Both strands are made without any RNA primers
- B. Okazaki fragments on the lagging strand remain unjoined
- C. The leading strand cannot be synthesised at all from the template
- D. The replication fork does not open at the origin
Q22. A mutation in the lac repressor gene prevents the repressor from binding the operator. In an E. coli cell with no lactose, what is the expected effect?
- A. Structural genes are never transcribed
- B. Transcription occurs only when lactose is added
- C. Structural genes are transcribed continuously
- D. The operator is deleted from the DNA
Q23. Which mutation is likely to be least harmful to the protein formed?
- A. Insertion of one nucleotide near the start of the coding region
- B. Insertion of two nucleotides in the middle of the coding region
- C. Deletion of one nucleotide near the start of the coding region
- D. Deletion of three adjacent nucleotides in the middle of a gene
Q24. A mutation changes the codon UAU (tyrosine) to UAG, where UAA, UAG and UGA are stop codons. What kind of mutation is this?
- A. A silent mutation, giving the same protein
- B. A missense mutation, giving one different amino acid
- C. A nonsense mutation, giving a shortened polypeptide
- D. A frameshift mutation, changing all later codons
Q25. A PCR reaction begins with one double-stranded template and runs for 10 cycles with perfect efficiency. How many copies of the target DNA are theoretically made, and why is Taq polymerase used?
- A. 10 copies; Taq polymerase is destroyed at each heating cycle
- B. 1,024 copies; Taq polymerase tolerates the denaturation step
- C. 1,024 copies; Taq polymerase needs no primers to start
- D. 100 copies; Taq polymerase works only at about 37 °C, body temperature
Q26. A circular plasmid has three EcoRI recognition sites. After complete digestion and gel electrophoresis, how many DNA bands (distinct fragments) are expected, and which travels farthest?
- A. Four bands, with the smallest fragment travelling farthest
- B. Three bands, with the largest fragment travelling farthest
- C. Three bands, with the smallest fragment travelling farthest
- D. Four bands, with the largest fragment travelling the farthest
Q27. Bacteria are transformed with a plasmid carrying an ampicillin resistance gene and lacZ, with a foreign gene inserted inside lacZ. On a plate with ampicillin and X-gal, which colonies carry the recombinant plasmid?
- A. White colonies, since the insert has disrupted lacZ
- B. Blue colonies, since X-gal is broken down
- C. No colonies, because ampicillin kills transformed cells
- D. All colonies, since both colours carry the insert
Q28. During a drought, finches on an island feed on large hard seeds, and the average beak depth in the next generation increases. This is an example of:
- A. genetic drift acting on neutral variation
- B. inheritance of acquired beak changes
- C. stabilising selection on heritable variation
- D. directional selection on heritable variation
Q29. Two frog species live in the same pond, but one breeds in spring and the other in late summer. Which type of reproductive isolation is this?
- A. Behavioural isolation, a postzygotic barrier
- B. Hybrid sterility, a postzygotic barrier
- C. Mechanical isolation, a prezygotic barrier
- D. Temporal isolation, a prezygotic barrier
Q30. Which pair of structures is homologous?
- A. The forelimb of a human and the flipper of a whale
- B. The fin of a shark and the tail of a dolphin, both used in swimming
- C. The eye of an octopus and the eye of a human, both used for vision
- D. The wing of a bat and the wing of a butterfly, both used in flight