NUMS — Medical & Dental Entry Test

NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 4)

Take the NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 4): 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. Two heterozygotes AaBb × AaBb are crossed (independent assortment, complete dominance). Among 320 offspring, how many are expected to be aaB_ (recessive for A, dominant for B)?
- A. 180
- B. 60 ✓
- C. 40
- D. 20
Answer: B. 60
Explanation: P(aa) = ¼ and P(B_) = ¾, so ³⁄₁₆ × 320 = 60.
Q2. A test cross AaBb × aabb gives 420 AB, 410 ab, 85 Ab and 85 aB offspring. What is the recombination frequency and what does it indicate?
- A. 17%, indicating the genes are linked on the same chromosome ✓
- B. 83%, indicating that the genes are tightly linked on one chromosome
- C. 50%, indicating that the genes assort independently on different chromosomes
- D. 17%, indicating independent assortment of genes on different chromosomes
Answer: A. 17%, indicating the genes are linked on the same chromosome
Explanation: Recombinants = 85 + 85 = 170 of 1000 = 17%. Frequencies well below 50% with parental classes dominating show linkage (map distance 17 cM).
Q3. Genes A, B and C are linked. Recombination frequencies are A–B 10%, B–C 5% and A–C 15%. What is the gene order?
- A. B–A–C
- B. A–C–B
- C. Cannot be determined
- D. A–B–C ✓
Answer: D. A–B–C
Explanation: The largest distance A–C (15) equals 10 + 5, so B lies between A and C.
Q4. A colour-blind-carrier woman (XᴴXʰ) marries a man with normal vision (XᴴY). What is the probability that a son is colour-blind?
- A. ½ ✓
- B. 1
- C. ¼
- D. 0
Answer: A. ½
Explanation: Sons receive the mother's X: half Xʰ, half Xᴴ, and the father's Y. P(colour-blind | son) = ½ (¼ of all children).
Q5. An autosomal recessive disease affects 1 in 2500 people in a population in Hardy–Weinberg equilibrium. About how many carriers are expected in 100 000 people?
- A. 4000 exactly
- B. 2000
- C. 3920 ✓
- D. 196
Answer: C. 3920
Explanation: q² = 1/2500 = 0.0004 → q = 0.02, p = 0.98. Carriers = 2pq = 2 × 0.98 × 0.02 = 0.0392 → 3920 per 100 000.

The other 25 questions

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Q6. In a population at equilibrium 8% of males have an X-linked recessive trait. What percentage of females is expected to express it?
- A. 0.64%
- B. 4%
- C. 16%
- D. 8%
Q7. A woman with blood group A and a man with blood group B have a child of group O. What is the probability that their next child is group AB?
- A. ¾
- B. ½
- C. ¼
- D. 0
Q8. Pink snapdragons (incomplete dominance) are crossed with red snapdragons. What fraction of offspring are pink?
- A. ¼
- B. ¾
- C. All
- D. ½
Q9. Three unlinked genes with additive alleles control a trait. For AaBbCc × AaBbCc, what fraction of offspring is homozygous for all six increasing alleles (AABBCC)?
- A. 1/8
- B. 1/32
- C. 1/16
- D. 1/64
Q10. A man has the karyotype 47,XXY. How many Barr bodies are expected in his somatic cells?
- A. Two
- B. One
- C. Three
- D. None
Q11. A diploid cell has 2n = 8. At metaphase I, how many bivalents and how many chromatids are present in the cell?
- A. 4 bivalents and 8 chromatids
- B. 8 bivalents and 16 chromatids
- C. 8 bivalents and 8 chromatids
- D. 4 bivalents and 16 chromatids
Q12. The ovarian cycle of a woman lasts 32 days, and the luteal phase is a constant 14 days. On which day of the cycle is ovulation expected?
- A. Day 16
- B. Day 20
- C. Day 18
- D. Day 14
Q13. A contraceptive pill combining oestrogen and progesterone prevents pregnancy mainly because
- A. it raises LH to exhaust the follicle, so no egg is left to be released
- B. it causes the corpus luteum to enlarge, so that ovulation is delayed until later
- C. negative feedback suppresses FSH and LH, so no LH surge and no ovulation
- D. it kills sperm in the uterus, so fertilisation cannot take place after ovulation
Q14. A urine pregnancy test detects a hormone secreted by the trophoblast shortly after implantation. This hormone
- A. maintains the corpus luteum so progesterone continues to be made
- B. is oestrogen secreted by the placenta, which thickens the endometrium
- C. is LH from the pituitary, which stimulates ovulation each month
- D. is FSH from the pituitary that stimulates a new follicle to develop
Q15. A man has a vasectomy. Which change is expected?
- A. Semen volume falls to zero
- B. Ejaculate lacks sperm, but testosterone levels remain normal
- C. FSH levels rise because Sertoli cells die
- D. Testosterone levels fall because Leydig cells are cut
Q16. Following fertilisation, the oocyte membrane depolarises and cortical granules release enzymes. What is the main function of this response?
- A. To prevent polyspermy by hardening the zona pellucida
- B. To bring about cleavage of the zygote
- C. To trigger the acrosome reaction
- D. To promote implantation
Q17. In a flowering plant with 2n = 24, how many chromosomes are present in an endosperm cell, and why?
- A. 48, from two sperm nuclei fusing with the diploid egg cell
- B. 36, from two polar nuclei (n each) fused with one sperm (n)
- C. 24, because the endosperm develops from the diploid zygote
- D. 12, because the endosperm forms from one sperm nucleus alone
Q18. In a Meselson–Stahl experiment, bacteria grown for generations in ¹⁵N are transferred to ¹⁴N and allowed to divide three times. What proportion of DNA molecules is hybrid (¹⁵N/¹⁴N)?
- A. 12.5%
- B. None
- C. 50%
- D. 25%
Q19. E. coli has a 4.6 million bp circular chromosome replicated bidirectionally from one origin by forks moving at 1000 nucleotides per second. About how long does replication take?
- A. About 19 minutes
- B. About 38 minutes
- C. About 77 minutes
- D. About 4.6 minutes
Q20. The template strand 3′-TACGGATTT-5′ is transcribed. What peptide is made, given codons AUG = Met, CCU = Pro, AAA = Lys?
- A. Met–Pro–Lys
- B. Met–Pro–Phe
- C. Met–Gly–Lys
- D. Tyr–Gly–Phe
Q21. A mutation deletes one nucleotide in the middle of a coding sequence. Compared with a substitution of one nucleotide, the deletion is generally more harmful because
- A. it changes only the first codon
- B. it shifts the reading frame for all following codons
- C. it always creates a stop codon at once
- D. it removes the promoter
Q22. Starting with one DNA molecule, how many copies are theoretically present after 30 PCR cycles?
- A. About 30
- B. About 900
- C. About 6.0 × 10⁵
- D. About 1.07 × 10⁹
Q23. In a PCR run, no product forms. The annealing temperature was set at 85 °C instead of about 55 °C. Why?
- A. The nucleotides are denatured at 85 °C, so none are available for the polymerase
- B. The DNA strands cannot separate at 85 °C, so the template stays double-stranded
- C. Taq polymerase is denatured at 85 °C and therefore cannot synthesise any DNA
- D. Primers cannot bind to the single-stranded template at such a high temperature
Q24. A linear 6 kb DNA is cut with an enzyme with two recognition sites, and the same enzyme cuts a circular 6 kb plasmid at two sites. How many fragments will be produced in each case?
- A. 3 fragments from each
- B. 2 fragments from each
- C. 3 fragments from the linear DNA; 2 from the plasmid
- D. 2 from the linear DNA; 3 from the plasmid
Q25. DNA fragments of 500 bp, 1500 bp and 3000 bp are run on an agarose gel. Which statement describes the result?
- A. Smaller fragments run further towards the positive electrode
- B. All fragments run the same distance
- C. DNA runs towards the negative electrode
- D. Larger fragments run further towards the positive electrode
Q26. To make human insulin in bacteria, researchers use cDNA rather than the genomic gene. What is the reason?
- A. Bacteria cannot remove introns from pre-mRNA
- B. Bacteria lack ribosomes
- C. cDNA is more stable than plasmid DNA
- D. Bacteria cannot transcribe DNA
Q27. The bat wing and the human arm share the same skeletal pattern, whereas the bat wing and the insect wing do not. These are best described as
- A. analogous in the first pair and homologous in the second
- B. analogous in both pairs
- C. homologous in the first pair and analogous in the second
- D. homologous in both pairs
Q28. A fossil bone has 25% of the carbon-14 it originally contained. If the half-life of ¹⁴C is 5730 years, how old is the bone?
- A. 17 190 years
- B. 5730 years
- C. 22 920 years
- D. 11 460 years
Q29. A few individuals from a mainland population colonise a distant island and the island population differs in allele frequencies from the mainland, simply by chance. This is an example of
- A. gene flow from the mainland
- B. natural selection by predation
- C. directional mutation pressure
- D. founder effect, a type of genetic drift
Q30. An Rh-negative mother gives birth to an Rh-positive child. Why is anti-D given to her soon after delivery?
- A. To prevent the baby from making antibodies against its mother's red blood cells
- B. To change the baby's blood group from Rh-positive to Rh-negative after birth
- C. To destroy fetal Rh-positive cells in her blood before she makes memory cells
- D. To increase her own anti-Rh antibodies so that future fetuses are protected