A-Level Biology Topic 16: Inheritance MCQs – 30 Practice Questions with Answers (Cambridge 9700)

Free practice for Cambridge International AS and A Level Biology 9700 on inheritance, with every question followed by a short explanation to help you check your understanding.

Meiosis and Variation

Q1. What is meant by a haploid cell?

  • (A) a cell with two sets of chromosomes, denoted 2n
  • (B) a cell with no chromosomes at all
  • (C) a cell with a single set of chromosomes, denoted n
  • (D) a cell with four sets of chromosomes, denoted 4n in a healthy adult under normal conditions
Show Answer

Answer: C – Haploid (n) means one set of chromosomes, while diploid (2n) means two sets.

Q2. What are homologous chromosomes?

  • (A) two identical sister chromatids joined at a centromere in a healthy adult under normal conditions during normal activity in a typical mammal
  • (B) a pair of chromosomes, one from each parent, carrying genes for the same characteristics at the same loci
  • (C) any two chromosomes chosen at random from a cell
  • (D) chromosomes that are always found in gametes only
Show Answer

Answer: B – Homologous pairs consist of one maternal and one paternal chromosome with the same genes at the same loci.

Q3. Why is a reduction division needed during meiosis?

  • (A) so that gametes are haploid and the diploid number is restored at fertilisation
  • (B) so that gametes have twice as many chromosomes as body cells in a healthy adult under normal conditions
  • (C) so that fertilisation produces tetraploid offspring
  • (D) so that chromosome number doubles in every generation
Show Answer

Answer: A – Meiosis halves the chromosome number, preventing it doubling at each fertilisation.

Q4. During which stage of meiosis I do homologous chromosomes separate to opposite poles?

  • (A) prophase I
  • (B) metaphase I
  • (C) telophase I
  • (D) anaphase I
Show Answer

Answer: D – Homologous chromosomes are separated in anaphase I, while sister chromatids separate later, in anaphase II.

Q5. During which stage of meiosis do homologous chromosomes pair up and crossing over occur?

  • (A) metaphase II
  • (B) prophase I
  • (C) anaphase II
  • (D) telophase II
Show Answer

Answer: B – Crossing over between homologous chromosomes occurs during prophase I.

Q6. How does crossing over produce genetically different gametes?

  • (A) by doubling the number of chromosomes in each gamete in a healthy adult under normal conditions
  • (B) by copying whole chromosomes without any change
  • (C) by preventing homologous chromosomes from separating
  • (D) by exchanging sections of DNA between homologous chromosomes, creating new allele combinations
Show Answer

Answer: D – Crossing over swaps DNA between homologues, producing chromatids with new combinations of alleles.

Q7. How does independent assortment produce genetically different gametes?

  • (A) because the orientation of each homologous pair at metaphase I is random
  • (B) because all maternal chromosomes always go to the same gamete in a healthy adult under normal conditions
  • (C) because sister chromatids never separate
  • (D) because gametes are formed by mitosis
Show Answer

Answer: A – Random orientation of homologous pairs at metaphase I gives many possible chromosome combinations in gametes.

Q8. How does random fertilisation contribute to genetic variation?

  • (A) because fertilisation always joins identical gametes
  • (B) because fertilisation halves the chromosome number again in a healthy adult under normal conditions during normal activity in a typical mammal
  • (C) because any male gamete may fuse with any female gamete, producing many possible genotype combinations
  • (D) because fertilisation prevents crossing over
Show Answer

Answer: C – Random fusion of gametes at fertilisation adds further variation beyond meiosis alone.

Q9. How many cells are produced at the end of meiosis from one original diploid cell, and what is their chromosome number?

  • (A) four haploid cells
  • (B) two diploid cells
  • (C) four diploid cells
  • (D) two haploid cells
Show Answer

Answer: A – Meiosis consists of two divisions and produces four genetically different haploid cells.

Q10. What happens to the nuclear envelope during meiosis, in outline?

  • (A) it remains intact throughout both divisions
  • (B) it breaks down before chromosome separation and reforms around the new nuclei
  • (C) it disappears permanently after the first division in a healthy adult under normal conditions
  • (D) it fuses with the cell surface membrane
Show Answer

Answer: B – The nuclear envelope breaks down to allow spindle formation and chromosome movement, then reforms around daughter nuclei.

Genetic Crosses and Terms

Q11. What is meant by an allele?

  • (A) the position of a gene on a chromosome
  • (B) the observable characteristic of an organism in a healthy adult under normal conditions
  • (C) a chromosome with no genes on it
  • (D) one of the different forms of a gene, found at a particular locus
Show Answer

Answer: D – An allele is a variant form of a gene; its position is its locus.

Q12. What is the difference between genotype and phenotype?

  • (A) genotype is observable and phenotype is hidden in a healthy adult under normal conditions during normal activity in a typical mammal
  • (B) genotype refers only to dominant alleles
  • (C) genotype is the genetic constitution of an organism, while phenotype is its observable characteristics
  • (D) phenotype is the same as genotype in all cases
Show Answer

Answer: C – Genotype is the alleles an organism possesses, while phenotype is what is expressed, influenced by genotype and environment.

Q13. An organism has two different alleles for a gene. What is its genotype described as?

  • (A) homozygous dominant
  • (B) heterozygous
  • (C) homozygous recessive
  • (D) codominant, in all cases
Show Answer

Answer: B – Heterozygous means two different alleles at a locus; homozygous means two identical alleles.

Q14. In a monohybrid cross between two heterozygotes for a gene with complete dominance, what phenotypic ratio is expected in the offspring?

  • (A) 3 dominant phenotype to 1 recessive phenotype
  • (B) 1 dominant phenotype to 1 recessive phenotype
  • (C) all dominant phenotype, with no recessive offspring
  • (D) 1 dominant phenotype to 3 recessive phenotype
Show Answer

Answer: A – A heterozygous cross gives genotypes 1 AA : 2 Aa : 1 aa, which is 3 dominant : 1 recessive in phenotype.

Q15. What is codominance?

  • (A) a situation where only the dominant allele is expressed
  • (B) a situation where neither allele is expressed
  • (C) a situation where alleles are found on different chromosomes in a healthy adult under normal conditions
  • (D) a situation where both alleles in a heterozygote are fully expressed in the phenotype
Show Answer

Answer: D – In codominance, both alleles contribute to the phenotype, rather than one masking the other.


Q16. What is a test cross?

  • (A) a cross between two homozygous recessive individuals only in a healthy adult under normal conditions during normal activity in a typical mammal
  • (B) a cross used only to study sex linkage
  • (C) a cross with a homozygous recessive individual, used to find the genotype of an individual showing the dominant phenotype
  • (D) a cross between two individuals of unknown phenotype
Show Answer

Answer: C – A test cross reveals whether a dominant-phenotype individual is homozygous or heterozygous.

Q17. In a dihybrid cross between two heterozygotes for two unlinked genes with complete dominance, what phenotypic ratio is expected?

  • (A) 9 : 3 : 3 : 1
  • (B) 3 : 1
  • (C) 1 : 1 : 1 : 1
  • (D) 9 : 1
Show Answer

Answer: A – Independent assortment of two unlinked genes gives the classic 9 : 3 : 3 : 1 phenotypic ratio.

Q18. What is autosomal linkage?

  • (A) genes located on different chromosomes always assorting independently
  • (B) genes located on the same autosome tending to be inherited together
  • (C) genes located on sex chromosomes only
  • (D) genes that are never inherited together
Show Answer

Answer: B – Linked genes are on the same chromosome and tend to be inherited together, unless crossing over separates them.

Q19. If two linked genes show recombinant offspring, what does this indicate?

  • (A) the genes are on different chromosomes in a healthy adult under normal conditions
  • (B) no meiosis has taken place
  • (C) the genes are codominant
  • (D) crossing over has occurred between the genes during meiosis
Show Answer

Answer: D – Recombinant phenotypes from linked genes arise when crossing over exchanges alleles between homologues.

Q20. What is epistasis?

  • (A) a situation where two alleles are both fully expressed
  • (B) a situation where genes are linked on the same chromosome in a healthy adult under normal conditions
  • (C) a situation where one gene masks or modifies the expression of another gene
  • (D) a situation where a gene has many alleles in a population
Show Answer

Answer: C – In epistasis, the effect of one gene depends on, or is masked by, another gene.

Genes, Phenotype and Gene Control

Q21. In a sex-linked cross, why are recessive sex-linked conditions usually more common in males than in females?

  • (A) males have two X chromosomes, so the allele is always masked in a healthy adult under normal conditions
  • (B) males have only one X chromosome, so a single recessive allele is expressed
  • (C) females never inherit sex-linked alleles
  • (D) males pass their X chromosome to all their sons
Show Answer

Answer: B – A male with one copy of a recessive X-linked allele shows the condition, while a female usually needs two copies.

Q22. What is the chi-squared test used for in genetics?

  • (A) to test whether observed results differ significantly from expected results
  • (B) to calculate the exact genotype of every offspring in a healthy adult under normal conditions
  • (C) to prove that a hypothesis is certainly correct
  • (D) to measure the rate of crossing over directly
Show Answer

Answer: A – The chi-squared test compares observed and expected numbers to judge whether a difference is likely due to chance.

Q23. How does the TYR gene relate to albinism, in outline?

  • (A) a faulty TYR gene causes excess haemoglobin production in a healthy adult under normal conditions during normal activity in a typical mammal
  • (B) a faulty TYR gene prevents blood clotting
  • (C) a faulty TYR gene causes uncontrolled cell division
  • (D) a faulty TYR gene means tyrosinase is not made correctly, so melanin production is reduced or absent
Show Answer

Answer: D – TYR codes for tyrosinase, an enzyme in melanin synthesis; loss of function leads to albinism.

Q24. How does the HBB gene relate to sickle cell anaemia, in outline?

  • (A) a change in the HBB gene prevents insulin production
  • (B) a change in the HBB gene stops melanin synthesis
  • (C) a change in the HBB gene alters haemoglobin, so red blood cells become sickle-shaped under low oxygen conditions
  • (D) a change in the HBB gene causes blood to clot too quickly in a healthy adult under normal conditions during normal activity in a typical mammal
Show Answer

Answer: C – HBB codes for part of haemoglobin; the sickle cell allele changes haemoglobin structure and red cell shape.

Q25. How does the F8 gene relate to haemophilia, in outline?

  • (A) a faulty F8 gene means factor VIII, a blood clotting factor, is not made correctly
  • (B) a faulty F8 gene means tyrosinase is absent
  • (C) a faulty F8 gene means huntingtin protein is altered in a healthy adult under normal conditions
  • (D) a faulty F8 gene means haemoglobin is absent
Show Answer

Answer: A – F8 codes for factor VIII, needed for blood clotting, so faults in F8 cause haemophilia.

Q26. What is the difference between a structural gene and a regulatory gene?

  • (A) a structural gene never codes for a protein
  • (B) a regulatory gene is found only in eukaryotes
  • (C) a structural gene controls other genes and a regulatory gene codes for enzymes in a healthy adult under normal conditions
  • (D) a structural gene codes for a protein such as an enzyme, while a regulatory gene controls the expression of other genes
Show Answer

Answer: D – Structural genes produce proteins, while regulatory genes control when and how much those genes are expressed.

Q27. What is the difference between an inducible enzyme and a repressible enzyme?

  • (A) an inducible enzyme is always present and a repressible enzyme is never present in a healthy adult under normal conditions during normal activity in a typical mammal as described for ordinary physiological conditions
  • (B) an inducible enzyme is normally absent and is made when its substrate is present, while a repressible enzyme is normally made and is switched off when its product is abundant
  • (C) both types are controlled only by temperature
  • (D) an inducible enzyme is made only in eukaryotes
Show Answer

Answer: B – Inducible and repressible enzymes illustrate different forms of gene control in response to conditions.

Q28. In the lac operon of a bacterium, what happens when lactose is absent?

  • (A) the structural genes are transcribed continuously at full rate in a healthy adult under normal conditions
  • (B) lactose binds to the promoter and starts transcription
  • (C) a repressor protein binds to the operator, preventing transcription of the structural genes
  • (D) the operon is permanently deleted from the DNA
Show Answer

Answer: C – Without lactose, the repressor blocks transcription; when lactose is present it binds the repressor, allowing transcription.

Q29. What are transcription factors in eukaryotes?

  • (A) enzymes that break down mRNA in the cytoplasm
  • (B) proteins that carry amino acids to ribosomes
  • (C) DNA sequences that code for ribosomal RNA only in a healthy adult under normal conditions
  • (D) proteins that bind to DNA and increase or decrease the rate of transcription
Show Answer

Answer: D – Transcription factors bind to DNA and regulate gene expression by changing transcription rate.

Q30. How does gibberellin activate genes in plants, in outline?

  • (A) it causes the breakdown of DELLA protein repressors, which normally inhibit factors that promote transcription
  • (B) it binds directly to ribosomes and stops translation in a healthy adult under normal conditions during normal activity in a typical mammal
  • (C) it destroys the genes that promote growth
  • (D) it prevents all transcription in stem cells
Show Answer

Answer: A – Gibberellin promotes breakdown of DELLA repressors, freeing transcription factors that promote growth genes.

Work through any questions you missed again, then revise those areas before moving on to the next topic.