Which measure is used to describe how genetically similar two individuals are, often used in twin studies?

• A. Concordance rate
• B. Genetic similarity
• C. Heritability
• D. Genotype

Answer: (B)

Genetic similarity describes how alike two people's genes are, and that’s the measure used in twin studies to assess how closely related two individuals are at the genetic level. In twin designs, identical twins share nearly all their genes, while fraternal twins share about half on average, so the degree of genetic similarity helps researchers infer how much genetics contribute to a trait.

Concordance rate looks at whether both twins show a trait, which tells you about similarity in expression but not the actual genetic relatedness. Heritability is about the proportion of variation in a trait across a population due to genetic differences, not how similar two individuals are genetically. Genotype refers to the actual genetic makeup of an individual, not a comparison between two people.