Everyone is familiar with DNA to a certain point. It is the the code that every cell of your body carries. If it breaks or changes due to some external “force” your cells are not going to function properly. This change can happen because of random mutation what can happen when your tissues are growing and your cells are dividing or because of some external DNA modification, like UV radiation, chemicals, oxidative damage, viruses. We have repair mechanisms to correct these, but if the mechanism fails, and sometimes fails due to too many mutations present at a time or because the mechanism itself gets damaged, this can happen naturally with age, the mutation remains in the cell. If the cell divides it can be passed down.
Getting a mutation is not necessarily means you will find changes in your system, not even if you are born with them.
Having the template for something doesn’t mean your cells are going to use it, or use all that they have. Different types of cells need different building blocks, proteins for their functionality. Most of our cells have the same DNA in every one of them (are some exceptions), but we still have different organs with different functionality. This difference can be achieved by selecting what part of the DNA the particular cell or is using. The part of the DNA that is not used is packed tightly, cant be accessed easily. The part that is used is “unpacked” it allows the proteins to access it and to get the information the cells need take care of it’s functionalities.
With our lifestyle, day-to-day choices we have (to a certain degree) control over what parts of our DNA is accessible and what part is packed away. This is epigenetics. With it you have power in your hands to have favorable and not favorable changes on your DNA usage in your cells. These changes can be passed down to your children too. Good news is good changes tend to stay longer, not favorable ones can be changed faster.
What you do matters, more than what you were born with.