Sheena and tina are identical twins who developed from a single zygote and share identical dna. nevertheless, as they develop, differences in physical and psychological characteristics become evident. these differences are due to:

These differences are due to the different environmental factors the twins are exposed to in their lifetimes. 

Environmental factors that affect physical characteristics include the food that they eat, the air that they breathe and even exercise habits.

Environmental factors that affect psychological characteristics include the different experiences they may have in life, possibly because of staying in different locations with different environments.

Hope this helps! :)