Twin boys both have a gene associated with aggressive tendencies. what is the most likely outcome to be observed in their behavior as they grow up?

It is not possible to determine the twins' behaviors based on having this single gene.

Explanation:

Even though both boys are meant to have a gene that is associated with aggressive tendencies, this is only a single gene. A single gene has very little impact once we combine it with the impact of all genes, as well as with the cultural influences and social context that the boys will grow up in. These characteristics are much more likely to determine the future behaviour of the twins. Therefore, we can conclude that we cannot possibly determine what their behaviour will be like based on a single gene.

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