How does effect DHT on these follicles?
Some of the hair follicles which have genetically tendency are rich of 5 alpha reductose enzyme and this enzyme is responsible of the transaction of testesteron to DHT. DHT gets connected to receptor and by effecting the cell metabolism causes to stop the normal cycles of hair.

In the early stages of hair loss, hair becomes thinner (miniaturization) and loses its pigment and becomes lighter colour. The hair on the backside and above the ears (donor area) don’t contain 5 alpha reductose  therefore they do not fall down.

During the hair transplantation the necessity hair is taken from the backside hair. Despite there is being testesteron in that area after the transplantation those hair are not sensible to DHT. Therefore patient don’t lose his hair.

It is not predictable when hair loss starts, when stops. What is important here is genetic potential.