Questions: Explain how an individual's phenotype may be determined by multiple genes that interact with one another and with the environment. Tongue rolling was thought to be an example of a human trait controlled by a single gene, but we now know that identical twins, who share 100% of their DNA sequences, will only share the tongue-rolling trait 70% of the time. This indicates that tongue rolling may also be controlled by the environment.

The answer is True: Tongue rolling was thought to be an example of a human trait controlled by a single gene, but we now know that identical twins, who share 100% of their DNA sequences, will only share the tongue-rolling trait 70% of the time. This indicates that tongue rolling may also be controlled by the environment.

Explanation:

• True: This statement is correct because the fact that identical twins, who have identical genetic makeup, do not always share the tongue-rolling trait suggests that environmental factors play a role in the expression of this trait. If tongue rolling were solely determined by genetics, identical twins would exhibit the trait 100% of the time.

• False: This option is incorrect because it ignores the evidence that environmental factors influence the expression of the tongue-rolling trait, as demonstrated by the 70% concordance rate among identical twins.

In summary, the observation that identical twins do not always share the tongue-rolling trait supports the idea that both genetic and environmental factors contribute to the expression of this phenotype.