210)Even when a trait is highly heritable, it can still be modified by the environment. 211)It is impossible to know just how a particular individual’s genes and personal history have interacted to produce him or her. 212)The most effective approach to estimate the heritability of a trait or behaviour is to compare blood relatives within families. 213)Adopted children are studied to investigate heritability because they share an environment with their adoptive parents and siblings, but they don’t share their genes. 214)The heritability of a trait can be estimated by comparing groups of same-sex fraternal twins with groups of identical twins. 215)Monozygotic twins develop when a fertilized egg divides into two parts that develop into separate embryos. 216)Dizygotic twins develop when a fertilized egg divides into two parts that develop into separate embryos. 217)Dizygotic twins develop when separate eggs are fertilized by separate sperm. 218)Monozygotic twins develop when separate eggs are fertilized by separate sperm. 219)An intelligence quotient is a measure of intelligence originally computed by dividing a person’s mental age by his or her chronological age and multiplying the result by 100.