§ So GI is a digestion system, like a stomach?

 The stomach is the GI track.

But you called it, the digestion system, nerve system, bone is a system?

No, bone is the structure, muscle is the structure, from the last question I say. Systems are like, lymph system, blood system, nerve system, digestion system, reproduction systems.

So you know about these systems?

I just explain to you some definition of words, your health class middle school, might just all have it defined for you, if you keep the textbooks.

So is there a way, DNA can change all these systems, DNA makes RNA, makes amino acid, there is no words in the system.

Correct, you mean proteins in the system to do some part of mechanism. Its too trivial size. The system is almost like your are living balance or equilibrium with your weight. If you are too heavy weight, is your blood pressure high? When the blood pressure high, you have some sympton of everything the hospital told you to do a check up. Sometimes they do some blood works.

Can DNA modify these system to make us healthier, that is what I want to say.

Most people have disease its because of their diet. Some are even more so, are their negative thinking, or very permissive types of character. When the mind works are weak, like you do things with cigarette, or drugs, or alochol, you are weak nature to cause some social burden others have to look after you. DNA does not change the habits, why you want to get a drink in the bar. Just one drink.