Biology • Year 12 • Module 6 • Lesson 4
Chromosomal Mutation — Large-Scale Genetic Change
Lock in the four structural categories — deletion, duplication, inversion, translocation — and the scale logic that separates chromosomal mutation from point mutation.
1. Label the four chromosomal mutation types
The diagram below shows a normal chromosome at the top and the four structural rearrangements below it. Each rearrangement is shown with the original gene-segment order labelled A · B · C · D · E. Write the missing labels into boxes A–H. 8 marks
- A — mutation name (segment missing) _______________________
- B — gene-content consequence of A (e.g. genes lost / extra copies / order reversed / moved away) _______________________
- C — mutation name (segment present twice) _______________________
- D — gene-content consequence of C _______________________
- E — mutation name (segment reversed in order) _______________________
- F — gene-content consequence of E _______________________
- G — mutation name (segment moved to another chromosome) _______________________
- H — gene-content consequence of G _______________________
| 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: chromosomal mutation, deletion, duplication, inversion, translocation, gene dosage, point mutation, karyotype, breakpoint, aneuploidy. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | A large-scale change to the structure of a chromosome segment — and sometimes to chromosome number — rather than a single base sequence. | |
| 2.2 | A chromosomal mutation in which a segment of a chromosome is lost, removing the genes in that region. | |
| 2.3 | A chromosomal mutation in which a chromosome segment is present twice, increasing the copy number of the genes in that region. | |
| 2.4 | A chromosomal mutation in which a segment breaks off and reattaches in the reverse orientation, changing gene order. | |
| 2.5 | A chromosomal mutation in which a segment moves to a different chromosome or new location, often onto a non-homologous chromosome. | |
| 2.6 | The number of copies of a gene present, which can affect how much gene product is made. | |
| 2.7 | A mutation at the level of a single base or a few adjacent bases within one gene, such as a substitution or small indel. | |
| 2.8 | An organised photographic image of all the chromosomes of a cell arranged in homologous pairs, used to detect large-scale changes. | |
| 2.9 | The exact location on a chromosome where a structural mutation breaks the DNA; a gene or regulatory region sitting across one can be disrupted. | |
| 2.10 | A condition in which a cell has one too few or one too many chromosomes relative to the species' normal number (e.g. trisomy 21). |
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 8 marks (1 for T/F, 1 for the correction where needed)
3.1 A chromosomal mutation is just a "bigger version" of a point mutation that happens to occur on a chromosome. T / F
3.2 A duplication of a chromosome segment increases the gene dosage of the genes inside that segment. T / F
3.3 Every inversion mutation causes severe disease because gene order is altered. T / F
3.4 Translocation moves a chromosome segment to a different location, sometimes onto a non-homologous chromosome. T / F
4. Effect recall — why does each change matter?
Answer each in 1–2 sentences using precise terms from the lesson. 10 marks (2 each)
4.1 What is the likely cellular effect of a deletion that removes a segment containing several genes?
4.2 What is the likely cellular effect of a duplication that doubles the copy number of a gene that controls cell growth?
4.3 What is the likely effect of an inversion whose breakpoints fall inside a gene's coding sequence?
4.4 What is the likely effect of a translocation that places a growth-control gene next to a strong "always-on" regulatory region from another chromosome?
4.5 Why does the same logic not usually apply to a single missense substitution in one codon of one gene?
5. Cloze paragraph — scale and consequence
Complete the paragraph by writing the missing word from the word bank into each numbered blank. Word bank (use each once): point, chromosomal, many, deletion, duplication, inversion, translocation, dosage, structure, broader. 10 marks (1 per blank)
A 5.1 _______________ mutation changes a single base — or just a few — inside one gene, while a 5.2 _______________ mutation changes the 5.3 _______________ of a chromosome segment, and sometimes chromosome number. Because 5.4 _______________ genes can sit inside one altered region, the biological consequences are usually 5.5 _______________ than those of a point mutation. The four structural categories are 5.6 _______________ (segment lost), 5.7 _______________ (segment present twice), 5.8 _______________ (segment reversed) and 5.9 _______________ (segment moved elsewhere). A duplication is especially likely to alter gene 5.10 _______________, because the extra copies can drive higher levels of gene product.
Q1 — Labelled diagram
A: deletion. B: genes inside the lost segment are removed entirely (gene content reduced). C: duplication. D: extra copies of the genes in that segment — gene dosage increased. E: inversion. F: gene order along the chromosome is reversed; if a breakpoint falls inside a gene or its control region, that gene may be disrupted. G: translocation. H: the segment of genes is moved to a new chromosomal context, often onto a non-homologous chromosome, sometimes placing genes next to new regulatory regions.
Q2 — Term–definition matches
2.1 chromosomal mutation • 2.2 deletion • 2.3 duplication • 2.4 inversion • 2.5 translocation • 2.6 gene dosage • 2.7 point mutation • 2.8 karyotype • 2.9 breakpoint • 2.10 aneuploidy.
Q3 — True / false with correction
3.1 False. Correction: a chromosomal mutation is not just a bigger point mutation — it is a structural change at the level of a chromosome segment (and sometimes whole chromosome number), so it can simultaneously affect many genes rather than altering one codon in one gene.
3.2 True.
3.3 False. Correction: not every inversion causes severe disease. Many inversions are carried without symptoms — the phenotypic effect depends on whether a breakpoint falls inside a gene or regulatory region.
3.4 True.
Q4.1 — Effect of deletion (2 marks)
If the deleted segment contains several genes, those gene products are no longer made [1]. Missing gene products or regulatory elements can disrupt development, cell function or both, and the effect is usually broader than losing one codon's worth of sequence [1].
Q4.2 — Effect of duplication (2 marks)
Doubling the gene copy number increases gene dosage, so substantially more growth-control protein may be produced [1]. Over-expression of a growth-control gene can push the cell toward inappropriate division and is a known route to abnormal proliferation in some cancers [1].
Q4.3 — Effect of an inversion with breakpoints inside a gene (2 marks)
A breakpoint inside a coding sequence physically cuts the gene, destroying the correct open reading frame [1]. The resulting truncated or fused mRNA usually produces a non-functional or aberrant protein, so that gene's function is lost or altered even though the rest of the chromosome looks intact [1].
Q4.4 — Effect of a translocation placing a growth-control gene under a strong promoter (2 marks)
The translocation moves the growth-control gene next to a strong regulatory region from another chromosome, so the gene is now transcribed at much higher levels than normal [1]. Continuous expression of a growth-control gene can drive uncontrolled cell division — this is the logic behind translocation-associated cancers such as the Philadelphia chromosome [1].
Q4.5 — Why a single missense substitution differs (2 marks)
A missense substitution changes only one codon and therefore (at most) one amino acid in one protein [1]. The effect is local to that one gene product — it cannot remove, duplicate, reverse or relocate multiple genes at once, so its biological consequences are usually narrower than those of a chromosomal mutation [1].
Q5 — Cloze paragraph (10 marks)
5.1 point • 5.2 chromosomal • 5.3 structure • 5.4 many • 5.5 broader • 5.6 deletion • 5.7 duplication • 5.8 inversion • 5.9 translocation • 5.10 dosage.