The human body is not a set of LEGO bricks assembled by our DNA instruction booklet.
You can't just say "I don't want this blue brick here, this gene correlated with manic depression" and have that be the extent of the affect on our future child.
There is not a 1-1 mapping from a gene or a DNA molecule or a set of genes to a characteristic of our phenotype.
As our body is built, all the different genes are interacting with the other genes and it's quite a mess to untangle what came from where. There's no single quality in the end state that came from any single quality of the start state. Scale that up, there's no set of qualities at the end state that came from any set smaller than the whole at the start state. It all interacted with all else along the way.