Compare and contrast twin designs and adoption designs. What conclusions can be drawn from each design about the relative influence of genetics and the environment on development?

Question

What will be an ideal response?

Answer 1

The ideal answer should include:
1. In twin designs, identical twins share 100 percent of their genes and fraternal twins only share 50 percent. In one type of twin designs, identical and fraternal twins who are reared in the same home are compared on various traits.
2. In comparison studies, if identical twins are more similar on a given physical or psychological trait than fraternal twins, it provides evidence that genes make an important contribution to that trait.
3. In some twin design studies, identical twins who are reared apart are compared to fraternal twins who are reared together. If identical twins who are reared apart are more similar to one another compared to fraternal reared together, the role of genetics is highlighted.
4. Because the environments of identical twins may be more similar than those of fraternal twins, the twins reared apart design is an important method of examining whether identical twins are still more similar than fraternal twins even when raised in different homes and cultural environments.
5. In adoption designs, a comparison is made between the child's psychological traits and those of the adoptive parent, who shares no genes but raised the child, and the biological parent, who shares 50 percent of the child's genes but did not raise the child.
6. A positive correlation between the biological parent and the child on a particular trait indicates a genetic influence. A positive correlation between the adoptive parent and child on a particular trait indicates an environmental influence.