NUMS — Medical & Dental Entry Test

NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 7)

Take the NUMS Biology — Reproduction, Inheritance, Evolution and Biotechnology (Set 7): 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 phenotypically normal parents have a child with an autosomal recessive disease. Their other child is phenotypically normal. What is the probability that this normal child is a carrier?
- A. 2/3 ✓
- B. 3/4
- C. 1/4
- D. 1/2
Answer: A. 2/3
Explanation: Both parents are Aa. Among normal offspring the genotypes are AA : Aa : Aa = 1 : 2, so the chance of being a carrier is 2/3 (not 1/2).
Q2. Two parents are both heterozygous for two unlinked recessive disease genes (AaBb × AaBb). What is the probability that a child is affected by at least one of the two diseases?
- A. 9/16
- B. 1/16
- C. 7/16 ✓
- D. 3/16
Answer: C. 7/16
Explanation: P(not affected by A) = 3/4 and same for B, so P(unaffected by both) = 9/16; P(at least one disease) = 1 − 9/16 = 7/16.
Q3. A colour-blind man (XᶜY) and a woman who is a carrier of the recessive colour-blindness allele (XᶜX) have children. What is the probability that a child (sex not specified) is a colour-blind girl?
- A. 1/4 ✓
- B. 1/2
- C. 1/8
- D. 3/4
Answer: A. 1/4
Explanation: Cross XᶜY × XᶜX gives XᶜXᶜ : XᶜX : XᶜY : XY in equal proportion, so a colour-blind daughter (XᶜXᶜ) has probability 1/4.
Q4. One parent has blood group A and the other has blood group B. Their first child has group O. What is the probability that their next child has group AB?
- A. 1/4 ✓
- B. 1/8
- C. 0
- D. 1/2
Answer: A. 1/4
Explanation: The O child shows that the parents are IᴬI and IᴮI. Gametes Iᴬ or i crossed with Iᴮ or i give IᴬIᴮ with probability 1/4.
Q5. Red-flowered snapdragons (RR) are crossed with white-flowered (rr), giving pink F₁ plants showing incomplete dominance. If an F₁ plant is crossed with a white plant, what offspring ratio is expected?
- A. 1 red : 2 pink : 1 white
- B. 1 red : 1 white
- C. 1 pink : 1 white ✓
- D. 3 pink : 1 white
Answer: C. 1 pink : 1 white
Explanation: Rr × rr gives 1/2 Rr (pink) and 1/2 rr (white).

The other 25 questions

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Q6. A test cross of AaBb with aabb gives 420 AaBb, 420 aabb, 80 Aabb and 80 aaBb among 1000 offspring. What is the recombination frequency?
- A. 84%
- B. 16%
- C. 8%
- D. 32%
Q7. Recombination frequencies between three linked genes are: A–B 10%, B–C 6% and A–C 16%. What is the order of the genes?
- A. B–A–C
- B. Cannot be determined
- C. A–C–B
- D. A–B–C
Q8. Cystic fibrosis (autosomal recessive) affects 1 in 2500 people in a population in Hardy–Weinberg equilibrium. What percentage of the population are carriers?
- A. About 7.8%
- B. About 0.04%
- C. About 2%
- D. About 3.9%
Q9. In a population of 1000 plants there are 160 AA, 480 Aa and 360 aa. Is the population in Hardy–Weinberg equilibrium for this gene?
- A. No, because heterozygotes are not the majority in the sample
- B. No, because there are fewer AA than aa plants in the sample
- C. Yes, as p = 0.4 and expected numbers match the observed ones
- D. Yes, because p = 0.5 and the genotype numbers are all equal
Q10. Three consecutive nucleotides that make up exactly one codon are deleted from the middle of a coding region. What is the most likely result?
- A. No change at all because of the degeneracy of the code
- B. A premature stop codon in every case without exception
- C. Loss of one amino acid, with the reading frame kept
- D. A frameshift changing all the following amino acids
Q11. How many Barr bodies are found in the nuclei of the somatic cells of a person with the karyotype 47, XXY and of a person with 45, X? (Number of Barr bodies = number of X chromosomes − 1.)
- A. None and one
- B. One and none
- C. Two and one
- D. One and one
Q12. A cell with 2n = 8 is in metaphase II of meiosis. How many chromosomes and how many chromatids does it contain?
- A. 8 chromosomes and 16 chromatids
- B. 8 chromosomes and 8 chromatids
- C. 4 chromosomes and 4 chromatids
- D. 4 chromosomes and 8 chromatids
Q13. A diploid cell has 6 pg of DNA in G₁. How much DNA is in one cell at metaphase of meiosis I, and in one gamete?
- A. 6 pg and 3 pg
- B. 6 pg and 1.5 pg
- C. 12 pg and 6 pg
- D. 12 pg and 3 pg
Q14. From 100 primary spermatocytes and 100 primary oocytes, how many mature gametes of each kind can result?
- A. 400 sperm and 400 ova
- B. 400 sperm and 100 ova
- C. 100 sperm and 100 ova
- D. 200 sperm and 100 ova
Q15. A woman has a regular 32-day cycle. Assuming that the luteal phase (ovulation to the next menstruation) is always 14 days, on which day of the cycle (day 1 = first day of menstruation) does ovulation occur?
- A. Day 16
- B. Day 18
- C. Day 20
- D. Day 14
Q16. A woman who breastfeeds frequently often has no ovulation for several months after delivery. Which mechanism best explains this?
- A. Suckling raises prolactin and reduces GnRH release, so FSH and LH stay low
- B. Suckling raises progesterone and corpus luteum growth, so FSH stays high
- C. Suckling lowers prolactin and reduces GnRH release, so FSH and LH stay low
- D. Suckling raises oestrogen and increases GnRH release, so FSH and LH stay high
Q17. In a pregnant woman the corpus luteum is surgically removed at week 5 in one case and at week 16 in another. What is expected?
- A. Pregnancy continues at both times
- B. Miscarriage at week 5, but pregnancy continues at week 16
- C. Pregnancy continues at week 5, but miscarriage at week 16
- D. Miscarriage at both times
Q18. Sea urchin eggs have their cortical granules removed. After the sperm is added, what is expected?
- A. No sperm enter, because the acrosome reaction fails
- B. One sperm enters and the egg divides normally afterwards
- C. The egg develops by parthenogenesis without any sperm
- D. Several sperm enter the egg, as the polyspermy block fails
Q19. After a vasectomy, a man's sperm count in semen is zero, but his testosterone level and sexual drive are normal. Why?
- A. Sertoli cells still release testosterone into the semen, though sperm cannot be made
- B. Leydig cells stop making testosterone, though sperm are still made
- C. Leydig cells still make testosterone, though sperm cannot pass the cut vas
- D. Seminiferous tubules still release testosterone, though FSH is absent
Q20. In a flowering plant with 2n = 14, how many chromosomes are present in the endosperm nucleus and in the embryo cells?
- A. 14 in the endosperm and 21 in the embryo
- B. 21 in the endosperm and 14 in the embryo
- C. 7 in the endosperm and 14 in the embryo
- D. 21 in the endosperm and 7 in the embryo
Q21. A flower is small and green with no scent, has long hanging stamens producing huge amounts of light, dry pollen, and a large feathery stigma. It is most likely pollinated by:
- A. moths
- B. birds
- C. bees
- D. wind
Q22. E. coli grown for many generations in ¹⁵N medium is moved to ¹⁴N medium and allowed to replicate three times. What fraction of the DNA molecules are hybrid (¹⁵N/¹⁴N)?
- A. 1/2
- B. 1/8
- C. 3/4
- D. 1/4
Q23. A mutant cell lacks DNA ligase. Short DNA fragments accumulate during replication. What are these fragments?
- A. RNA primers that were not made by the enzyme primase
- B. Okazaki fragments of the lagging strand that have not been joined
- C. Leading strand pieces that were wrongly cut by nucleases
- D. Exons that were not spliced from the primary transcript
Q24. In Marfan syndrome a mutation in one gene causes tall stature, long fingers, lens dislocation in the eye and weakness of the aorta wall. Which term describes one gene affecting several traits?
- A. Polygenic inheritance, many genes together shaping a single trait
- B. Codominance, both alleles being fully expressed in a heterozygote
- C. Epistasis, one gene masking the expression of a different gene
- D. Pleiotropy, one gene influencing several different traits
Q25. A DNA mixture containing fragments of 500, 1500 and 3000 base pairs is separated by agarose gel electrophoresis. Which statement is correct?
- A. The 3000 bp fragment is nearest the well and all fragments move towards the positive electrode
- B. The 500 bp fragment is nearest the well and all fragments move towards the positive electrode
- C. All fragments stay at the well because DNA is neutral
- D. The 3000 bp fragment is farthest from the well and all fragments move towards the negative electrode
Q26. A circular plasmid of 4000 bp is digested with a restriction enzyme and electrophoresis shows two bands, of 1000 bp and 3000 bp. What does this show?
- A. The enzyme cuts the plasmid at one site
- B. The plasmid is linear with one cut site
- C. The enzyme cuts the plasmid at two sites
- D. The enzyme does not cut the plasmid
Q27. To make human insulin in bacteria, the gene is usually obtained as cDNA made from mRNA rather than from genomic DNA. Why?
- A. Bacteria cannot translate exons, which cDNA lacks
- B. Bacteria cannot remove introns, which cDNA lacks
- C. Bacteria cannot use promoters, which cDNA contains
- D. Bacteria cannot transcribe DNA, which cDNA lacks
Q28. In regions where malaria is common, the sickle-cell allele remains at a high frequency even though homozygotes (HbˢHbˢ) are often severely ill. What is the best explanation?
- A. Heterozygotes cannot be infected, so they have no cost
- B. Heterozygotes are more resistant to malaria, so selection favours them
- C. Homozygotes are more resistant to malaria, so selection favours them
- D. The mutation rate is high, so the allele keeps arising
Q29. The eye of an octopus and the eye of a human are both camera-type eyes, but they evolved independently. These eyes are an example of:
- A. vestigial structures resulting from divergent evolution
- B. analogous structures resulting from divergent evolution
- C. homologous structures resulting from convergent evolution
- D. analogous structures resulting from convergent evolution
Q30. A new island population was founded by five individuals from a large mainland population. An allele that is rare on the mainland (1%) is found at 20% on the island. This is an example of:
- A. gene flow bringing the allele from the mainland
- B. the founder effect, a type of genetic drift
- C. mutation increasing the allele by chance
- D. natural selection favouring the allele on the island