There has yet been no known attempt to conduct germline gene therapy on a
human embryo. Medical science has not yet advanced far enough to do such a
procedure safely. However, it is inevitable that science will progress far
enough that parents will be able to actually determine the genetic makeup of
their children. They will be able to do this for either therapeutic (i.e. to
weed out certain genetic disorders) or for what are called cosmetic reasons
(i.e. hair color, eye color, intelligence, and so on.)
Germline gene therapy for therapeutic reasons would not only weed out
genetic traits for such inherited diseases such as down syndrome or hemophilia,
but even the predisposition to catch diseases such as cancer and Alzheimers
later in life. The implications of a widespread use of such therapy would mean
that many diseases that afflict human beings would become far rarer or even
nonexistent.
Some parents will be tempted to design their children with other traits. If
potential parents want blond haired, blue eyed children, they would be able to
get them. They could order other traits such as intelligence, athletic ability,
musical talent, physical beauty, and so on. Of course, many of these traits are
determined just as much by environment and nurturing as they are by ones
genetic makeup. What use, for example, is musical talent if it is never
nurtured by training and exposure to great music?