Emma and Anna Are Identical Twins Who Were Adopted by Different

Multiple Choice

Emma and Anna are identical twins who were adopted by different families a few weeks after their birth. Although genetically identical, they grew up with different physical and psychological characteristics. For example, though both inherited a tendency to grow large, Anna was slim and athletic because of the active lifestyle practiced in her adoptive family. This variability can be explained by how

A) each zygote is unique.
B) longevity genes can make an individual less vulnerable to certain diseases.
C) for each genotype, a range of phenotypes can be expressed.
D) mutated genes can be a source of genetic variability.