What type of twins had a concordance rate of 17% in the Gottesman and Shields study?

• A. MZ twins
• B. DZ twins
• C. Fraternal twins
• D. Adoptive twins

Answer: (B)

In the Gottesman and Shields study, the concordance rate of 17% pertains specifically to dizygotic (DZ) twins. This finding indicates that when one twin in a pair of DZ twins shows a particular trait or disorder, there is a 17% likelihood that the other twin will also exhibit the same trait or disorder.

Dizygotic twins are the result of two separate eggs being fertilized by two separate sperm cells, which means they share about 50% of their genetic material. This lower concordance rate compared to monozygotic (MZ) twins—who share nearly 100% of their genetic material—provides insights into the genetic versus environmental influences on traits and disorders. The study illustrates how genetic factors may play a role in the development of certain conditions, but environmental and social factors are equally significant, particularly given the differences observed when comparing concordance rates between MZ and DZ twins.

In summary, the 17% concordance rate in DZ twins reinforces the understanding that genetic predisposition does not solely determine outcomes and highlights the importance of studying different types of twins to disentangle the effects of genetics and environment on behavior and psychological conditions.