Biology • Year 11 • Module 3 • Lesson 14
Molecular Evidence
Lock in the core vocabulary, the logic of sequence comparison, the roles of cytochrome c, mitochondrial DNA, the molecular clock, BLAST and DNA barcoding as tools for evolutionary study.
1. Term–definition match
The eight definitions below are shuffled. In the right-hand column write the matching term from this list: DNA hybridisation, amino acid sequencing, cytochrome c, molecular clock, genetic divergence, DNA barcoding, mitochondrial DNA (mtDNA), BLAST. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | A technique that identifies species using a short, standardised DNA sequence (commonly the CO1 gene in animals) that can be matched against a reference library. | |
| 1.2 | Using known mutation rates to estimate the time since two lineages diverged from a common ancestor. | |
| 1.3 | A protein found in all aerobic organisms that performs the same role in cellular respiration and whose amino acid sequence can be compared across species. | |
| 1.4 | Determining the order of amino acids in a protein so that the sequence can be compared between species as evidence of relatedness. | |
| 1.5 | The accumulation of genetic differences between two populations or lineages after they stop or reduce interbreeding. | |
| 1.6 | DNA located in mitochondria that is usually inherited from the mother and mutates at a relatively fast rate, useful for tracing recent lineages. | |
| 1.7 | An online tool that aligns a query DNA or protein sequence against databases of known sequences to identify closest matches. | |
| 1.8 | Measuring genetic similarity by heating mixed DNA strands from two species and noting the temperature at which they separate. |
2. 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 correction where needed)
2.1 Greater sequence similarity between two species always means their DNA is identical. T / F
2.2 Cytochrome c is useful for evolutionary comparison because it is found in all aerobic organisms and its amino acid sequence varies slightly between species. T / F
2.3 Mitochondrial DNA is typically inherited from both parents equally. T / F
2.4 DNA barcoding can identify a species even when the whole organism is not available or when morphology is misleading. T / F
3. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
3.1 What does high DNA sequence similarity between two species suggest about their evolutionary relationship?
3.2 Why is cytochrome c particularly useful for comparing a wide range of species, including very distantly related organisms?
3.3 Why is mitochondrial DNA useful for tracing lineages over relatively recent evolutionary time?
3.4 In what situations is DNA barcoding more useful than morphological identification?
4. Cloze — complete the paragraph
Fill each blank with the correct word from the word bank below. Use each word once only. 8 marks
Word bank: ancestor | barcoding | convergent | cytochrome c | diverged | maternal | mutations | sequences
Molecular evidence uses DNA and protein to reveal evolutionary relationships. The central idea is that species sharing a more recent common will have fewer differences in their sequences because fewer have accumulated since they . The protein is found across all aerobic organisms, making broad cross-species comparisons possible. Mitochondrial DNA is particularly useful because it is usually inherited through the line, allowing researchers to trace lineages across generations. DNA is another molecular tool that identifies species from a short DNA sequence, especially useful when morphology is absent or misleading. Morphological similarity can be deceptive because evolution can produce similar-looking structures in unrelated lineages.
Q1 — Term–definition matches
1.1 DNA barcoding • 1.2 molecular clock • 1.3 cytochrome c • 1.4 amino acid sequencing • 1.5 genetic divergence • 1.6 mitochondrial DNA (mtDNA) • 1.7 BLAST • 1.8 DNA hybridisation.
Q2 — True / False with correction
2.1 False. Correction: greater sequence similarity means the DNA sequences are more alike, not identical. Closely related species have fewer sequence differences, but some mutations will have accumulated since they diverged.
2.2 True.
2.3 False. Correction: mtDNA is usually inherited from the mother only (maternal inheritance). It does not generally track paternal lineages, which is why it is useful for reconstructing maternal lines and lineage tracing.
2.4 True.
Q3.1 — DNA sequence similarity and relatedness
High DNA sequence similarity suggests the two species share a more recent common ancestor. Fewer sequence differences have accumulated because the lineages diverged only recently and there has been less time for mutations to build up independently in each lineage.
Q3.2 — Why cytochrome c is broadly useful
Cytochrome c is found in all aerobic organisms and performs the same essential role in cellular respiration in all of them. Because it is universal, its amino acid sequence can be compared across a vast range of species — from bacteria to primates — making it one of the most powerful single-molecule tools for estimating broad evolutionary relationships.
Q3.3 — Why mtDNA is useful for lineage tracing
mtDNA is maternally inherited (not recombined from two parents), so it passes largely unchanged down the female line. It also tends to mutate faster than much nuclear DNA, meaning differences accumulate more quickly — making it useful for distinguishing populations that diverged relatively recently and for tracing maternal lineages including patterns of human migration.
Q3.4 — When DNA barcoding is preferred
DNA barcoding is more useful when the organism is damaged, processed (e.g. filleted fish), at an immature or larval stage, or too small to identify reliably from physical appearance. It is also used when investigating illegal wildlife trade, food fraud, or when two species look so similar that morphology is ambiguous.
Q4 — Cloze answers (in order of blanks)
sequences • ancestor • mutations • diverged • cytochrome c • maternal • barcoding • convergent