In other words, Luckylee, Garry hasn't got a clue. It's not his field of expertise.
DNA can be read; it doesn't have to be read. As best we can tell, one copy of a chromosome is held as a kind of backup while the other is read and used; its genes are expressed in a given cell.
For a gene to be expressed, it must contain information pertinent to the cell's function. Every cell in your body contains information coding for liver enzymes; only liver cells "express" those genes. DNA is turned on and off according to what tissue type it is in.
As to your third question, only further research can answer that question as you have stated it.
As to our fourth question, the choices of which copy to use are likely made randomly in each tissue and cell type. Dominant genes will be expressed unless they are turned "off" by come cellular mechanism. Hair and eye color are examples of this. Certain colors are dominat while others are recessive. If a single copy of the dominant gene is inherited, it will be expressed. In order for the recessive gene to be expressed you have to have both recesive alleles.
I don't know what you mean by invalid chromosomes. There are proteins that arise with tumors that the immune system can recognize as foreign and attack, but the proteins have to be formed in the cells from RNA using DNA as a template. The seeds of our own destruction are carried within our own cells, in that regard. They may have gotten there by means of viruses. What it takes to stimulate their production is the purview of oncologists.
I hope that helps.
