Set 11: Transitions
Explanation
PASSAGE
Mitochondrial DNA is inherited exclusively from the mother, making it useful for tracing maternal lineages. Mutations accumulate at a relatively constant rate, allowing researchers to estimate when populations diverged. _______ 'Mitochondrial Eve'—the most recent common maternal ancestor of all living humans—is estimated to have lived approximately 200,000 years ago in Africa.
Which choice completes the text with the most logical transition?
Detailed Answer Explanation
This question asks you to choose the transition that best connects two ideas. The mutation rate (molecular clock) enables dating. 'Using this molecular clock' shows how the method produces the specific estimate. Transitions signal the relationship between sentences or paragraphs. Determine the logical relationship (addition, contrast, cause-effect, example) and select the transition that accurately expresses it. The right transition makes the relationship between ideas crystal clear. Consider what logical connection exists: Is the second idea adding to the first? Contrasting it? Showing a result? The transition should accurately reflect this relationship.
Key Evidence:
• "Mutations accumulate at a relatively constant rate"
• "estimated to have lived approximately 200,000 years ago"
Why others are wrong: B (Contrast - the estimate follows from the methodology.), D (Contrast - there's no unexpected element here.), C (Example - while the Eve estimate is an application, 'Using this molecular clock' better shows the causal connection.).
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