Using your knowledge of genotype and phenotype, explain why identical twins may have different personalities.

As identical (monozygotic) twins share 100% of the same genetic material, we can say that their genotype is identical. However, this is only an example of how nature can influence behaviour that is partly genetically determined, such as behaviours linked with personality (predisposition to be more aggressive due to candidate genes). If these twins were separated at birth and were subject to different contextual environments, it is clear that nurture may also have a role in the development of personality. In this case therefore, it could be that the different environments in which each twin was raised could to an extent have an effect on their overall personalities, shaped by the environment they grew up in. Therefore their genes may be expressed differently depending on the environment (phenotype), leading to different personalities.