Question

Can you have too much DNA?

Answer 1

Yes, if by that you mean that DNA additions can cause disease.
When a full chomosome gets added, like for instance in the case of a trisomy, you can get serious manifestation, like the typical example of Down's syndrome. In this syndrome, one has three pairs of chromosome 21, instead of two. But in other cases, just a few added nucleotides can also add up op to very serious diseases.

Answer 2

yes eg in diseses like heamophilia, this in a condition where the female is the carrier ie she does not suffer from the disease but becase she has more chromosomes it can cause the infant to have heamophilia if he is male. ie male are mainly suifferers of the disease.