Prof. Dr. Sohan Raj Tater
Invariably genetic Engineering involves DNA modifications. DNA is the genetic material in all known forms of lives. DNA contains genes (just as a recipe book contains recipes) that give us many of our physical characteristics. However we are not simply genes based machines—the environment we are in also determines our traits. One of the challenges of Genetic Engineering is to determine how genes influence our traits and how to modify DNA to alter these traits. Genes affecting disorders such as alcoholism provide only predisposition. Having the gene for alcoholism may make one prone to alcoholism but does not guarantee that one will become alcoholic, nor does not having the gene mean one is immune.
An important distinction in Genetic Engineering is between germline and non-gemline cells. In most organisms, there are cells set aside just for reproduction. These are eggs and sperms in human. Non germline cells are all the other cells in the body - muscle cells, skin cells, liver cells etc. If a genetic modification does not alter germline cells, it should not have any effect on the genetic make up of future generations (there are some possible exceptions to this). Thus, if one were to introduce the gene for purple hair, but the parent would. If the gene for purple hair were introduced into the parental germline cells, then the children could carry the purple hair gene.
This is complicated in plants because while many plants have germline cells. They can also be propogated asexually by cuttings. Additionally, it is possible to clone animals from single cells. Thus it is possible to clone a mouse from even non-germline cells. So even though introducing the purple hair gene into hair cell is not a strictly heritable alteration, it is still possible to grow a whole mouse from a single hair cell (not a hair cell, not a strand of hair).
Doctoral Thesis, JVBU