Final answer:
The correct answer is a) Genetic variance. This term represents the extent to which variation in intelligence test scores can be attributed to genetic differences, which is significant according to studies on twins such as the Minnesota Study of Twins Reared Apart.
Step-by-step explanation:
The intelligence test scores of fraternal twins, who share only about half their genes, are much less similar. Estimates of the heritability of intelligence- the extent to which intelligence test score variation can be attributed to genetic variation is what the question is seeking. The correct answer is a) Genetic variance.
In the Minnesota Study of Twins Reared Apart and other behavioral genetics research, it has been observed that identical twins, whether raised together or apart, generally show higher similarity in intelligence test scores than fraternal twins or siblings. This suggests that genetics play a substantial role in determining intelligence, although environmental factors also contribute to an individual's intellectual development. The concept of Range of Reaction supports the idea that while genetic factors set certain potential limits, the environment interacts with these genetic predispositions to shape the actual development of intelligence.