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.