The human body has been studied by scientists for several centuries now to learn more about it and how they function. This also helps in knowing the causes for some sicknesses which helps in finding a way to cure them. And other things this does is in understanding the reasons why people react differently to certain triggers like what happens in a food allergy.
This includes studying the genetics of humans which are basically the cells composing the body with the help of the life instructions coming from the DNA. Within them are several sequences which specifies the ways in making important proteins. Then there are epigenetics which affects essentially how cells read the genes to produce proteins in certain methods.
There are many things that these changes do in affecting the life of a person through the reactions made during particular triggers. This includes life circumstances that can cause the genes in being expressed or silenced over time. It means they could be turned on and become active or turned off and become inactive then.
Everything around you affects your body such as the time you sleep, the place you live, the food you eat, the exercises you do and even aging. These factors can cause chemical modifications eventually around the genes which turn them off or on after a while. Certain diseases would switch them to their opposite state which was the normal or healthy one.
These changes makes individuals unique from other people by giving them specific physical features which are different from others. This even includes their preferences in food, socialization, personality, skills and talents. These different combinations of genes being active and dormant grants the uniqueness of a person and there are even indications that changes with it could be inherited as well.
Reversing them might also be despite the thousands of genes within the body and the variety of possible combinations of them being turned off or on. But if each cause and effect that the combinations have can be mapped by scientists and reversing their state is possible then they could eliminate the bad and keep the good ones. This may theoretically stop obesity, slow aging and cure cancer among other possibilities.
Compare it with movies with them being the span of a human life and the cells are the actors and actresses that are in them these are units essential in making up the movie and the DNA being the script of that story which states what each participant does in their roles. The sequences then would be the words written on the script.
Certain phrases in them with the instructions for certain key events or actions taking place will be the genes then. Scriptwriting then is comparable to genetics while epigentics is compared to directing the movie. This means the script may be the same for everyone but the director has the right to tweak or eliminate certain dialogue or scenes.
This is what makes each movie, or person different from one another. Even when the same story is being told, there are still differences between them depending on the storyteller. That is why identical twins are not entirely identical.