A Level H1 Biology Genetics Inheritance Quiz

A-Level Biology H1 Quiz - Genetics Inheritance (Answer Key)

Total Marks: 40
Topic: Genetics & Inheritance (Syllabus 8876 Core Idea 2)

Section A: Core Concepts (1–8)

Q1. [1 mark]
Answer: Mutation (or gene mutation if specifying DNA level).
Teaching note: A mutation is any permanent alteration in the nucleotide sequence of DNA. It can occur in a gene (gene mutation) or in chromosome structure/number.

Q2. [1 mark]
Answer: Down syndrome (trisomy 21).
Teaching note: Trisomy 21 is a numerical chromosomal aberration where an individual has three copies of chromosome 21 instead of two.

Q3. [1 mark]
Answer: DNA polymerase.
Teaching note: DNA polymerase synthesises the new strand by adding nucleotides complementary to the template, in the 5'→3' direction.

Q4. [1 mark]
Answer: An allele is an alternative form of a gene at a specific locus.
Teaching note: For example, a gene for flower colour may have a purple allele and a white allele.

Q5. [1 mark]
Answer: Frameshift mutation (specifically insertion frameshift).
Teaching note: Adding or deleting nucleotides not in multiples of three shifts the reading frame of codons downstream.

Q6. [1 mark]
Answer: Transcription.
Teaching note: Transcription produces pre-mRNA, which is processed into mRNA before translation.

Q7. [1 mark]
Answer: aa.
Teaching note: Homozygous means two identical alleles; recessive is denoted by lowercase.

Q8. [1 mark]
Answer: Multipotent stem cell (or blood stem cell / haematopoietic stem cell).
Teaching note: These are multipotent – they can form multiple blood cell types but not all cell types.

Section B: Interpretation (9–15)

Q9. [2 marks]
Answer: Autosomal recessive. [1]
Reason: Two unaffected parents (I-1 and I-2) produced an affected offspring (II-3), so the condition cannot be dominant; also affected individuals appear in both sexes equally, suggesting autosomal not X-linked. [1]
Marking: 1 for correct mode, 1 for valid pedigree-based reason.

Q10. [2 marks]
(a) [1] Substitution mutation.
(b) [1] The codon CCA codes for proline, while CTA codes for leucine; a different codon specifies a different amino acid, altering the primary protein structure.
Teaching note: Substitution changes one base, which may change one amino acid (missense) or none (silent).

Q11. [2 marks]
Answer: Genotype of purple parent = Pp (heterozygous). [1]
Reasoning: Test cross with pp (white) gave ~1:1 ratio (148:152 ≈ 1:1), which is the expected outcome when a heterozygote is crossed with a homozygous recessive. [1]
Working: If purple parent were PP, all offspring would be purple. Since half are white, it must carry p.

Q12. [3 marks]
Answer:

• Substitution of A→T changes codon GAG→GTG in β-globin mRNA. [1]
• This replaces glutamic acid with valine at position 6 of haemoglobin β-chain. [1]
• Valine is hydrophobic, causing haemoglobin to polymerise under low oxygen, distorting red cells into sickle shape and reducing oxygen transport. [1]
  Marking: 1 per point; accept equivalent detail.

Q13. [2 marks]
Answer: Gametes will contain either R or r (not Rr). [2 – 1 for each allele listed]
Teaching note: Homologous chromosomes separate in meiosis I; meiosis II separates sister chromatids, so each gamete gets one allele.

Q14. [2 marks]
Working:
A = 22%, so T = 22% (A=T). [1]
A+T = 44%, thus G+C = 56%.
G = C, so G = 28%. [1]
Answer: 28% guanine.

Q15. [2 marks]
Answer: Any two of: translocation, duplication, inversion, deletion. [1 each]
Teaching note: These are structural changes in chromosome arrangement, distinct from gaining/losing whole chromosomes.

Section C: Extended Reasoning (16–20)

Q16. [5 marks]
Answer:

• G1: cell grows, organelles replicate, normal metabolism. [1]
• S: DNA replication occurs, each chromosome becomes two sister chromatids. [1]
• G2: cell checks DNA, prepares for division. [1]
• M (mitosis): prophase, metaphase, anaphase, telophase; chromosomes segregated. [1]
• Significance: tight regulation prevents uncontrolled division (cancer), ensures accurate DNA distribution to daughter cells for growth/repair. [1]

Q17. [4 marks]
Answer:

• Benefit: informed reproductive choice, preparation for care, early intervention. [1]
• Autonomy: respect for parents’ decision-making. [1]
• Ethical concern: potential discrimination or termination based on disability. [1]
• Societal: equity of access to screening, stigmatisation of conditions like Down syndrome. [1]
  Marking: 1 mark per distinct consideration; accept other valid points.

Q18. [5 marks]
Answer:

• Transcription: DNA double helix unwinds; RNA polymerase builds pre-mRNA complementary to template strand; introns removed, exons spliced to form mRNA. [2]
• Translation: mRNA binds ribosome; tRNA with anticodon delivers amino acid; peptide bond forms; chain grows until stop codon; polypeptide released and folds. [3]
  Teaching note: Connects genotype to phenotype via protein synthesis.

Q19. [3 marks]
Answer:

• Climate change may favour curly hair (e.g., via selection if straight hair disadvantage), shifting phenotype frequency. [1]
• However, the graph shows phenotype frequency, not genotype; environmental effects or non-genetic factors could mimic change. [1]
• Limitation: without allele-frequency data across generations, we cannot confirm genetic evolution vs. phenotypic plasticity. [1]

Q20. [4 marks]
Answer:

• Accumulated mutations: multiple genes (oncogenes/tumour suppressors) must be damaged for cancer. [1]
• Angiogenesis: tumour secretes signals to grow new blood vessels for nutrient supply. [1]
• Metastasis: cells break away, travel via blood/lymph, colonise other tissues. [1]
• Together these explain progression from local growth to life-threatening disease. [1]