If a trait is influenced by genes, then it ought to be more highly correlated across pairs of __________ than across pairs of __________.

Question

BlackTom AI · Accepted Answer

Identical (monozygotic, MZ) twins share nearly 100% of their genes, whereas fraternal (dizygotic, DZ) twins share on average about 50% of segregating genes; therefore genetically influenced traits should show higher concordance in identical than in fraternal twins.

1. Relevant knowledge points and concepts
- Genetic relatedness: MZ twins ≈ 100% shared genes; DZ twins ≈ 50% (like ordinary siblings).  
- Heritability and correlation: If a trait has a genetic basis, the similarity (correlation or concordance) between two individuals tends to increase with genetic relatedness.  
- Twin method: Researchers compare correlations for MZ and DZ pairs to infer genetic influence. If r_MZ > r_DZ, that indicates genetic contribution.

2. Step-by-step reasoning
- Assume a trait is genetically influenced. Two people with more shared genes should show more similar trait values.  
- Compare pair types: MZ pairs have maximal genetic similarity; DZ pairs have roughly half that. So MZ correlations should exceed DZ correlations.  
- Thus the blanks should be filled with “identical twins” in the first blank and “fraternal twins” in the second.

3. Example calculation (intermediate steps)
- Suppose observed correlations: r_MZ = 0.8, r_DZ = 0.4. These numbers reflect greater similarity for MZ than DZ. Using Falconer’s estimate of heritability: h^2 ≈ 2(r_MZ − r_DZ) = 2(0.8 − 0.4) = 0.8, indicating strong genetic influence. The key point: r_MZ > r_DZ.

4. Why the correct answer is correct
- Because identical twins share twice as much genetic material as fraternal twins on average, any genetically influenced trait will be more highly correlated across identical twin pairs than across fraternal twin pairs (holding environment constant).

5. Why the other options are incorrect
- “Genetic siblings; fraternal twins”: fraternal twins are genetic siblings, so this phrasing is inconsistent and doesn’t capture the highest genetic similarity (MZ).  
- “Fraternal twins; identical twins”: reverses the logical order — it would predict greater correlation in fraternal than identical twins, contrary to genetic expectations.  
- “Adoptive siblings; genetic siblings”: adoptive siblings share environment but not genes; genetically influenced traits should correlate more in genetic siblings than in adoptive siblings.

6. Conclusion
This reasoning confirms the correct choice: identical twins; fraternal twins.

If a trait is influenced by genes, then it ought to be more highly correlated across pairs of than across pairs of .单项选择题

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If a trait is influenced by genes, then it ought to be more highly correlated across pairs of __________ than across pairs of __________.单项选择题