Biology • Year 12 • Module 6 • Lesson 5
Somatic vs Germ-Line Mutation; Coding vs Non-Coding DNA
Lock in the two dimensions of mutation significance: inheritance (somatic vs germ-line) and functional location (coding vs non-coding). Build the vocabulary needed to reject the two big misconceptions cleanly.
1. Build the two-by-two mutation grid
The lesson's core synthesis (Card 4) is that mutation significance depends on two independent dimensions. The grid below has the column and row headings missing, plus an empty cell in each quadrant. Fill in the eight blanks A–H using the lesson's exact vocabulary. 8 marks
| Column heading 1: A ______________ | Column heading 2: B ______________ | |
|---|---|---|
| Row heading 1: C ______________ (occurs in body cells) |
D — main consequence: ______________ (named example from lesson: ______________) |
E — main consequence: ______________ |
| Row heading 2: F ______________ (occurs in gametes / gamete-producing line) |
G — main consequence: ______________ | H — main consequence: ______________ (why this still matters even with no protein change: ______________) |
| Box | Your label |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: somatic mutation, germ-line mutation, coding DNA, non-coding DNA, regulatory region, promoter, gene expression, gamete, population relevance, allele. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | DNA sequence that contributes directly to the amino acid sequence of a protein. | |
| 2.2 | A mutation in a body cell; affects the individual but is not normally inherited by offspring. | |
| 2.3 | DNA sequence not translated into protein, but often important for regulation, timing and genome function. | |
| 2.4 | Whether a mutation can enter the gene pool and affect future generations. | |
| 2.5 | A mutation in a gamete or gamete-producing cell line; can be passed to offspring. | |
| 2.6 | Control of when, where and how strongly a gene is expressed. | |
| 2.7 | A haploid sex cell (e.g. sperm or egg) that carries hereditary information to the next generation. | |
| 2.8 | A non-coding DNA element directly upstream of a gene where RNA polymerase binds to initiate transcription. | |
| 2.9 | A non-coding section of DNA (e.g. promoter, enhancer, splice site) that controls expression rather than coding for amino acids. | |
| 2.10 | An alternative version of a gene at a given locus. |
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 10 marks (1 for T/F, 1 for the correction where needed)
3.1 Any mutation that occurs in a body cell is automatically passed to that person's children. T / F
3.2 A mutation in non-coding DNA can never affect phenotype because it does not change amino acid sequence. T / F
3.3 A germ-line mutation can be inherited by offspring and so can enter the population gene pool. T / F
3.4 A UV-induced mutation in a skin cell is a germ-line mutation. T / F
3.5 A point mutation inside a gene's promoter can change how strongly the gene is expressed even if the coding sequence is unchanged. T / F
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 10 marks (2 each)
4.1 What is the biological role of coding DNA?
4.2 What is the biological role of non-coding regulatory DNA (e.g. promoters, enhancers)?
4.3 What is the function of distinguishing somatic from germ-line mutation when discussing inheritance?
4.4 What is the function of a mutation in a gamete for long-term genetic change in a population?
4.5 Why is the term "junk DNA" considered scientifically misleading at HSC level?
5. Cloze — the two-dimensional rule
Fill the eight blanks using the word bank: somatic, germ-line, coding, non-coding, regulation, gene pool, amino acid, two. Each word is used exactly once. 8 marks
A mutation matters differently depending on two things: which cells it occurs in, and where in the genome it sits. 5.1 ______________ mutations occur in body cells; they may affect the individual but are not normally inherited. 5.2 ______________ mutations occur in gametes or the gamete-producing lineage and can therefore be inherited by offspring and enter the 5.3 ______________. Independently of that, mutations in 5.4 ______________ DNA may change a codon and so alter the 5.5 ______________ sequence of a protein, while mutations in 5.6 ______________ DNA may instead alter the timing, location or strength of 5.7 ______________ — i.e. gene expression. The full HSC rule is therefore that mutation significance depends on 5.8 ______________ dimensions: inheritability and functional location.
6. Build a concept map
Draw labelled arrows between the five terms below to show how they connect. Each arrow must carry a linking phrase (e.g. "is inherited as", "may alter", "affects only"). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: somatic mutation · germ-line mutation · coding DNA · non-coding (regulatory) DNA · population gene pool.
Q1 — Two-by-two grid (8 marks)
A: Coding DNA (column 1). B: Non-coding DNA (column 2). C: Somatic mutation (row 1). D: May change amino acid sequence in a body-cell protein; example: a UV-induced skin-cell mutation contributing to skin cancer. E: May change gene expression / regulation in that tissue (still not normally inherited). F: Germ-line mutation (row 2). G: Can be inherited by offspring and may alter protein sequence across the whole organism. H: Can be inherited and may alter when/where/how strongly a gene is expressed in offspring; why this still matters: a non-coding mutation can change regulation (timing, location, strength of expression) even without changing the protein sequence itself. 1 mark each.
Q2 — Term–definition matches (10 marks)
2.1 coding DNA · 2.2 somatic mutation · 2.3 non-coding DNA · 2.4 population relevance · 2.5 germ-line mutation · 2.6 gene expression · 2.7 gamete · 2.8 promoter · 2.9 regulatory region · 2.10 allele.
Q3 — True / false with correction (10 marks)
3.1 False. Correction: only mutations in the germ-line (gametes or gamete-producing cell lineage) are normally inherited; mutations in other body cells (somatic mutations) usually affect the individual only.
3.2 False. Correction: non-coding DNA includes promoters, enhancers, splice sites and regulatory RNA genes — mutations here can still change phenotype by altering when, where or how strongly a gene is expressed.
3.3 True.
3.4 False. Correction: a UV-induced skin-cell mutation is a somatic mutation (skin cells are body cells, not gametes); it can contribute to skin cancer in the individual but is not normally inherited.
3.5 True.
Q4.1 — Role of coding DNA (2 marks)
Coding DNA carries the codon sequence that is transcribed into mRNA and translated at the ribosome to determine the amino acid sequence of a protein. A mutation in this region can therefore directly change protein structure or function (e.g. missense, nonsense, frameshift).
Q4.2 — Role of non-coding regulatory DNA (2 marks)
Non-coding regulatory DNA (promoters, enhancers, splice sites, regulatory RNA genes) controls when, where and how strongly a gene is expressed. A mutation here can therefore alter expression level, tissue specificity or RNA processing without changing the amino acid sequence of the protein.
Q4.3 — Function of the somatic vs germ-line distinction (2 marks)
The distinction matters because only mutations in the germ-line can enter offspring and the population gene pool. Somatic mutations may still cause disease (e.g. many cancers) but they are not inherited, so they do not contribute to long-term genetic change in a population.
Q4.4 — Function of a gamete mutation in long-term genetic change (2 marks)
A mutation in a gamete can be passed to offspring at fertilisation and so enters the population gene pool. Over generations, this is the only route by which mutation contributes to evolutionary change — somatic mutations end with the individual.
Q4.5 — Why "junk DNA" is misleading (2 marks)
Although some non-coding DNA may have little detectable effect, a substantial fraction has clear regulatory or functional roles (promoters, enhancers, splice sites, regulatory RNA genes). The HSC position is that it is wrong to claim non-coding DNA is automatically biologically unimportant.
Q5 — Cloze (8 marks)
5.1 Somatic · 5.2 Germ-line · 5.3 gene pool · 5.4 coding · 5.5 amino acid · 5.6 non-coding · 5.7 regulation · 5.8 two.
Q6 — Sample concept map (5 marks)
A correct map should include arrows such as:
- somatic mutation — affects only the individual; does NOT enter → population gene pool
- germ-line mutation — can enter → population gene pool
- somatic mutation or germ-line mutation — may occur in → coding DNA
- somatic mutation or germ-line mutation — may occur in → non-coding (regulatory) DNA
- coding DNA — mutation may alter amino acid sequence of → a protein (linking back to phenotype)
- non-coding (regulatory) DNA — mutation may alter timing/strength of → gene expression (and so phenotype)
Any biologically valid linking phrases are accepted. Award full marks for at least 5 correctly labelled arrows that respect causal direction.