Aubrey and Ava are identical twins who were raised in separate homes by their divorced parents. Now, as they enter elementary school, Aubrey shows mild symptoms of phenylketonuria (PKU), but Ava's symptoms are more severe. The girls have different phenotypes for this disease.

The question is incorrect. The complete question is as follows:

Aubrey and Ava are identical twins who were raised in separate homes by their divorced parents. Now, as they enter elementary school, Aubrey shows mild symptoms of phenylketonuria (PKU), but Ava's symptoms are more severe. The girls have different for this disease.

Phenotypes.

Explanation:

The genotype represents the genetic constitution of the individual whereas the phenotype represents the physical appearance of the individual. The genotype and environmental factors are responsible for the phenotype of an individual.

The phenylketonuria is the genetic disease that might occur due to the disrupt mechanism of the amino acid phenylalanine. The two girls have different symptoms for the disease that means they show the phenotypic differences bur their genetic constitution is same. This phenotypic difference might occur due to the different environmental conditions.

Thus, the answer is phenotype.