Explain how adoption, twin, and family studies shed light on the contributions of genetics and the environment to a person's development.
What will be an ideal response?
A good answer would include the following key points:
- Monozygotic twins share 100 percent of their genes in common, whereas dizygotic twins and nontwin siblings share 50 percent of their genes, and strangers share 0 percent of their genes. These facts set the stage for investigating the roles of genetics and the environment in shaping development.
- Monozygotic twins raised in the same environment wouldn't allow for the disentangling of genetic and environmental influences, given that both genes and environment are relatively constant for this group. However, monozygotic twins raised in different adoptive environments would allow an estimation of the relative contributions of genetic and environmental factors to development; genes are identical, environment differs.
- Comparing monozygotic and dizygotic twins within relatively the same environment allows for an estimation of genetic contributions; here genes differ (100 percent versus 50 percent) but environment stays the same.
- Comparing strangers within the same environment provides similar information; here there is no genetic overlap and constancy in the environment.
- One might imagine an "ideal" family composed of one set of monozygotic twins, one set of dizygotic twins, two nontwin siblings, two adopted siblings, and two non-sibling adoptees! All combinations of genetic and environmental experience could presumably be investigated.
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