Biology • Year 12 • Module 5 • Lesson 12
Proteins, Phenotype and Gene-Environment Interaction
Apply the genotype → protein → phenotype pathway to real data on height & nutrition, to a protein-shape stimulus, and to a diagram critique.
1. Interpret adult-height data across nutrition cohorts
Two groups of monozygotic (genetically identical) twins were raised in different countries. Group X grew up in a country experiencing chronic childhood malnutrition; Group Y grew up in a country with consistent, balanced childhood nutrition. The table below shows mean adult height for both groups, alongside a control group Z of unrelated individuals in the well-nourished country. 7 marks
| Group | Genetic background | Childhood nutrition | Mean adult height (cm) |
|---|---|---|---|
| X | MZ twin set A | Chronic malnutrition | 162 |
| Y | MZ twin set A (same as X) | Balanced, sufficient | 176 |
| Z | Unrelated controls | Balanced, sufficient | 175 |
1.1 Describe the pattern of mean adult heights across Groups X, Y and Z. 2 marks
1.2 Groups X and Y share an identical genotype. Using lesson content, explain why their adult heights differ. 3 marks
1.3 A student concludes: "Group X are genetically shorter than Group Y." Justify why this conclusion is not supported by the data. 2 marks
2. Interpret graph — enzyme shape, temperature and biological effect
The graph below shows the activity of a digestive enzyme at different body temperatures. Two curves are shown: the activity of a normal enzyme (solid green) and the activity of a variant enzyme that differs by a single amino acid in its active site (dashed purple). 6 marks
Stylised activity curves — illustrative of how a single amino acid change can shift an enzyme's optimum and reduce maximum activity.
2.1 At 37 °C, estimate the relative activity of the normal enzyme and the variant enzyme. 2 marks
2.2 Identify one structural change at the protein level that could explain the difference between the two curves. 2 marks
2.3 Using the lesson's genotype → protein → biological effect → phenotype pathway, predict one possible phenotypic effect on an organism carrying only the variant enzyme. 2 marks
3. Diagram critique — what's wrong with this student's diagram?
A Year 12 student has drawn the diagram below to explain how genes produce phenotype. There are three biological errors in the diagram. Identify each error and write the correction. 6 marks (2 per error: 1 identify, 1 correct)
3.1 Error 1: What is wrong?
Correction:
3.2 Error 2: What is wrong?
Correction:
3.3 Error 3: What is wrong?
Correction:
4. Apply to a new scenario — hydrangea flower colour
Hydrangea plants can produce blue, pink or purple flowers. The plants involved often share the same genotype, but soil pH (and the availability of aluminium ions) influences which pigment pathway is most active during flower development. In acidic soils, the flowers are typically blue; in alkaline soils, the same plant's flowers turn pink. 5 marks
4.1 Using the lesson's pathway (genotype → protein → biological effect → phenotype), explain where in the pathway the environment acts in this scenario. 2 marks
4.2 The gardener claims "the plant's DNA must change colour with the soil". Refute this claim using one sentence from the lesson on environment vs genotype. 2 marks
4.3 Name one other example from biology where a single genotype can produce different phenotypes in different environments. 1 mark
Q1.1 — Pattern of mean adult heights
Group X (genetically identical to Y but malnourished) has a much lower mean adult height (162 cm) than Group Y (176 cm). Group Y is essentially equal to the unrelated well-nourished controls (Group Z, 175 cm), differing by only 1 cm. The 14 cm difference between X and Y is therefore associated with nutrition rather than with genotype.
Q1.2 — Why X and Y differ (3 marks)
Groups X and Y carry the same alleles, so their potential height set by genotype is the same [1]. Adult height is the phenotypic outcome of a long developmental process driven by proteins (e.g. growth hormones, enzymes that build bone and cartilage, transport proteins delivering nutrients) that all depend on raw materials supplied by nutrition [1]. Chronic malnutrition limits these protein-driven growth processes so the genetic potential is not fully expressed, producing a lower phenotypic height — a clear example of environment influencing phenotypic expression without normally changing genotype [1].
Q1.3 — Refute "Group X are genetically shorter" (2 marks)
By design, X and Y share the same genotype (MZ twins of the same set) [1], so any difference in adult height cannot be attributed to genetic differences. The data show an environment-driven difference in phenotypic expression, not a genetic difference [1].
Q2.1 — Activity at 37 °C (2 marks)
Normal enzyme ≈ 95–100% relative activity (its peak sits at 37 °C) [1]; variant enzyme ≈ 30–40% (its lower peak is shifted to a cooler temperature, so at 37 °C it is well below maximum) [1]. Accept ±5 percentage points.
Q2.2 — Structural explanation (2 marks)
A single amino acid substitution in the active site changes the local shape of the enzyme [1], reducing how well the substrate fits and so reducing maximum catalytic activity; it can also alter the temperature at which the enzyme is most stable, shifting the peak to a different temperature [1].
Q2.3 — Predicted phenotypic effect (2 marks)
If the variant is the only form expressed, the protein-driven biological effect (the chemical reaction the enzyme catalyses) is less efficient at body temperature [1]. This can produce a phenotype consistent with reduced metabolic output of that pathway — for example, slower digestion or accumulation of unmetabolised substrate, depending on which pathway the enzyme serves [1]. Any plausible lesson-aligned phenotype accepted.
Q3 — Diagram critique (6 marks)
3.1 Error 1 (gene → trait with no protein): the diagram omits the critical intermediate step. Genes do not become traits directly. Correction: insert a "Protein (structure & function)" box and a "Biological effect" box between the gene and the trait, so the chain reads gene → protein → biological effect → phenotype. [1 + 1]
3.2 Error 2 ("Environment changes the DNA sequence during a person's life"): the environment does not normally change the genotype during ordinary development; it influences expression of the phenotype. Correction: redraw the environment arrow so it points to the phenotype (or to the protein/biological-effect step) — not to the DNA — and re-label it "environment influences phenotypic expression". [1 + 1]
3.3 Error 3 (caption — "identical genotype must give identical phenotype"): two organisms with the same genotype can produce different phenotypes in different environments (phenotypic plasticity). Correction: rewrite the caption as "Identical genotypes can produce different phenotypes in different environments because environment influences expression." [1 + 1]
Q4.1 — Where environment acts (2 marks)
Soil pH and aluminium ion availability do not change the plant's DNA sequence. Instead, they influence which protein-driven biochemical pathway (pigment synthesis) is most active in the developing flower [1]. Environment therefore acts at the "biological effect → phenotype" step (and indirectly at "protein activity"), modifying expression of the genotype-encoded pathway rather than the genotype itself [1].
Q4.2 — Refute "DNA must change colour" (2 marks)
The lesson states that "the environment does not normally change the genotype during ordinary development, but it can influence how the phenotype is expressed" [1]. The hydrangea's DNA is unchanged across soils; only the expression of pigment-producing protein activity differs, producing different colours from the same genotype [1].
Q4.3 — Another example (1 mark)
Acceptable examples include: Himalayan rabbit fur darkening at cool body extremities (temperature affects an enzyme), human skin tanning with sun exposure, identical-twin height differences after differing nutrition, Daphnia helmet formation in the presence of predator cues, or any other plausible phenotypic plasticity example [1].