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.

Phenotype of the organism is composite of observable characteristics or traits of the organism. The traits include morphology or the physical form and the structure of the organism; the developmental processes of the organism ; the biochemical and the physiological properties of the organism; the behavior and products of the behavior of the organism.

Organism's phenotype results from the two basic factors, which are:

Expression of an genetic code organism

Influence of the environmental factors.

Thus, both Aubrey and Ava have different phenotypes which leads to having different symptoms between them.