NUMS — Medical & Dental Entry Test

NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 5)

Take the NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 5): 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. A plant with genotype AB/ab in which genes A and B are linked and 20 map units apart is test-crossed with ab/ab. What percentage of its gametes are AB?
- A. 10%
- B. 20%
- C. 40% ✓
- D. 80%
Answer: C. 40%
Explanation: Recombinants total 20% (10% Ab, 10% aB), so parental gametes are 80%, split equally: AB 40% and ab 40%.
Q2. An autosomal recessive disorder affects 1 in 2,500 newborns in a population in Hardy–Weinberg equilibrium. About what proportion of the population are carriers?
- A. 1 in 100
- B. 1 in 2,500
- C. 1 in 50
- D. 1 in 25 ✓
Answer: D. 1 in 25
Explanation: q² = 1/2500, so q = 0.02 and p = 0.98. Carriers = 2pq = 2 × 0.98 × 0.02 = 0.039, or about 1 in 25.
Q3. A woman with normal vision, whose father was colour-blind, marries a man with normal vision. What is the probability that their first child is a colour-blind son?
- A. 1/8
- B. 1/2
- C. 1/4 ✓
- D. 0
Answer: C. 1/4
Explanation: Mother is X^C X^c, father is X^C Y. Of four equally likely offspring (X^C X^C, X^C X^c, X^C Y, X^c Y), only one is a colour-blind son: 1/4.
Q4. In a pedigree, a disorder affects only males, appears in every second generation, and is never passed from an affected father to his sons. Which mode of inheritance fits best?
- A. Y-linked
- B. Autosomal dominant
- C. Autosomal recessive
- D. X-linked recessive ✓
Answer: D. X-linked recessive
Explanation: Transmission through unaffected carrier females to half of their sons, with no father-to-son transmission, is typical of X-linked recessive traits.
Q5. Two parents with blood group A have a child with blood group O. What is the probability that their next child has blood group A?
- A. 3/4 ✓
- B. 1/4
- C. 1
- D. 1/2
Answer: A. 3/4
Explanation: The parents must both be I^A i. The cross gives 1 I^A I^A : 2 I^A i : 1 ii, so 3/4 are group A.

The other 25 questions

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Q6. Pink-flowered snapdragons (incomplete dominance) are crossed with red-flowered plants. Among 60 offspring, how many are expected to be red?
- A. 30
- B. 45
- C. 60
- D. 15
Q7. Skin colour in a model is controlled by three gene pairs with equal, additive effects (each dominant allele adds one unit). How many phenotypic classes can appear among the offspring of two AaBbCc parents?
- A. 27
- B. 6
- C. 8
- D. 7
Q8. Ignoring crossing over, how many genetically different gametes can one human produce because of independent assortment of the 23 chromosome pairs?
- A. About 8.4 million (2²³)
- B. About 46 thousand (46²)
- C. About 70 trillion (2⁴⁶)
- D. About 529 (23²)
Q9. A colour-blind boy has Klinefelter syndrome (XXY). His father and mother both have normal colour vision. Where did the non-disjunction most probably occur?
- A. In the father's meiosis I, giving a sperm with X and Y
- B. In the mother's meiosis II, giving an egg with two identical X^c
- C. In the mother's meiosis I, giving an egg with X^C and X^c
- D. In the father's meiosis II, giving a sperm with two Y chromosomes
Q10. Bacteria grown for many generations in ¹⁵N medium are transferred to ¹⁴N medium and allowed to divide four times. What is the ratio of light (¹⁴N/¹⁴N) to hybrid (¹⁴N/¹⁵N) DNA molecules?
- A. 7 : 1
- B. 3 : 1
- C. 15 : 1
- D. 1 : 1
Q11. Three nucleotides are inserted exactly between two codons in the middle of the coding region of a gene, in a way that creates no stop codon. What is the most likely effect on the protein?
- A. The protein is cut short by a premature stop codon
- B. One extra amino acid, and the rest of the sequence is unchanged
- C. Every amino acid after the insertion is changed
- D. One amino acid is changed, and the rest is unchanged
Q12. A point mutation changes a codon for tyrosine (UAC) to UAG. Which description applies?
- A. Missense mutation, which produces a different amino acid
- B. Frameshift mutation, which produces an altered protein
- C. Silent mutation, which produces the same protein
- D. Nonsense mutation, which produces a shortened protein
Q13. A PCR reaction starts with 8 template DNA molecules, and every cycle doubles the number of copies perfectly. How many copies are present after 5 cycles?
- A. 256
- B. 160
- C. 40
- D. 64
Q14. A linear DNA molecule of 10 kb is cut with a restriction enzyme and gives fragments of 2, 3 and 5 kb on a gel. How many recognition sites does the enzyme have in the molecule, and which band travels farthest?
- A. Two sites, and the 2 kb band travels farthest
- B. Two sites, and the 5 kb band travels farthest
- C. Three sites, and the 2 kb band travels farthest
- D. Three sites, and the 5 kb band travels farthest
Q15. Which sequence is most likely to be the recognition site of a restriction enzyme?
- A. 5′-GAATCC-3′, since it has equal numbers of purines and pyrimidines
- B. 5′-ACGTTA-3′, since it has equal numbers of G and C bases
- C. 5′-GAATTC-3′, since it reads the same on the opposite strand
- D. 5′-GATTAC-3′, since it has equal numbers of A and T bases
Q16. Bacteria are transformed with plasmids carrying an ampicillin-resistance gene and lacZ, in which a foreign gene was inserted. On plates with ampicillin and X-gal, which colonies carry the recombinant plasmid?
- A. Blue colonies, since the insert has disrupted lacZ
- B. White colonies, since the insert has disrupted lacZ
- C. Blue colonies, since the insert has activated lacZ
- D. White colonies, since the insert has deleted the ampicillin gene
Q17. Bt cotton makes a protein from Bacillus thuringiensis. What is the benefit of this protein to the crop?
- A. It makes the cotton tolerant of a herbicide
- B. It makes the cotton fix atmospheric nitrogen
- C. It makes the cotton fibres longer and stronger
- D. It kills bollworm larvae that eat the plant
Q18. In a paternity case, DNA fingerprint bands are: mother 1, 3, 5; child 1, 2, 5; man A 2, 4, 7; man B 4, 6, 7. Which conclusion is correct?
- A. Man B is excluded, but man A could be the father
- B. Both men could be the father
- C. Both men are excluded as the father
- D. Man A is excluded, but man B could be the father
Q19. After a severe drought on an island, the average beak depth of a finch population increases from 9.2 mm to 9.7 mm in the next generation. Which explanation is most consistent?
- A. Beaks deepened in individual birds, so the change was acquired and then inherited
- B. Large hard seeds remained, so deep-beaked birds survived better and reproduced more
- C. Small seeds remained, so shallow-beaked birds survived better and reproduced more
- D. Birds with deeper beaks migrated in, so allele frequencies changed by gene flow only
Q20. A horse and a donkey mate and produce a mule, which grows well but is sterile. In speciation terms, this is an example of
- A. prezygotic isolation, through behavioural differences
- B. postzygotic isolation, through hybrid breakdown in the F₂
- C. prezygotic isolation, through gametic incompatibility
- D. postzygotic isolation, through hybrid sterility
Q21. Cytochrome c sequences are compared with humans: chimpanzee 0 differences, rhesus monkey 1, dog 13, yeast 44. Which conclusion is best supported?
- A. Cytochrome c evolves at the same rate in every lineage
- B. Humans and yeast shared an ancestor more recently than humans and dogs
- C. Humans are more closely related to dogs than to rhesus monkeys
- D. Humans are more closely related to chimpanzees than to dogs
Q22. A rare allele is unusually common in a small isolated community founded by a few families. Which process best explains this?
- A. Gene flow, from a large neighbouring population
- B. Founder effect, a type of genetic drift
- C. Natural selection, favouring that allele in the new area
- D. Mutation pressure, at a very high rate in the community
Q23. An ovulated human egg is collected just after release from the follicle. In which stage of meiosis is the cell arrested?
- A. Metaphase I, as a primary oocyte
- B. Metaphase II, as a secondary oocyte
- C. Prophase I, as a primary oocyte
- D. Telophase II, as a mature ovum
Q24. How many sperm and how many functional ova are produced from 50 primary spermatocytes and 50 primary oocytes by complete meiosis?
- A. 50 sperm and 50 ova
- B. 100 sperm and 50 ova
- C. 200 sperm and 50 ova
- D. 200 sperm and 200 ova
Q25. A combined oral contraceptive containing oestrogen and progesterone prevents pregnancy mainly because it
- A. destroys the corpus luteum, so implantation cannot occur
- B. blocks the sperm receptors in the oviduct, so fertilisation fails
- C. raises FSH and LH by feedback, so ovulation occurs earlier
- D. suppresses FSH and LH by feedback, so ovulation does not occur
Q26. A urine test for pregnancy detects a hormone made soon after implantation. The hormone is secreted by
- A. the anterior pituitary, as LH that triggers ovulation
- B. the ovary, as oestrogen that thickens the endometrium
- C. the trophoblast cells, as hCG that maintains the corpus luteum
- D. the corpus luteum, as FSH that stimulates the follicle
Q27. After a sperm fuses with an egg, cortical granules release their contents and the zona pellucida hardens. What is the effect?
- A. It starts the second meiotic division of the sperm
- B. It blocks the entry of further sperm (polyspermy)
- C. It allows the entry of more sperm for faster fertilisation
- D. It attaches the embryo to the uterine wall
Q28. A flowering plant has a diploid number of 14. After double fertilisation, what are the chromosome numbers in the embryo and in the endosperm respectively?
- A. 7 and 14
- B. 14 and 14
- C. 14 and 21
- D. 21 and 14
Q29. A person has XY chromosomes and testes, but the cells lack functional androgen receptors, and the person has a female external appearance with no uterus. What explains the lack of male development?
- A. Cells cannot respond to testosterone, though the testes make it
- B. The Y chromosome is missing, so the testes never form
- C. The cells respond to testosterone, but there is excess oestrogen
- D. The testes do not make testosterone, because the SRY gene is absent
Q30. In the cross AaBbCc × AaBbcc (three independently assorting gene pairs, complete dominance), what proportion of the offspring show the dominant phenotype for A and B, and the recessive phenotype for C?
- A. 9/32
- B. 27/64
- C. 9/64
- D. 3/16