Your meaning, here is unclear, but if I understand it correctly, it is a mistake to describe a mutation as “a DNA defect”. Having taken a genetics class you should know that not all mutations are negative. Some have a positive effect (with respect to reproductive success) and the majority have no effect at all.
If you don't mind tell us your favorite ten "positive" mutations.
Maybe not ten off the top of my head, but here are a few.
All humans were once lactose intolerant. At several different places, several different mutations (new genes) have occurred. Each of which gave a specific population of humans the ability to consume milk into adulthood, and gave that population a distinct edge in competition for survival.
Further back in history, another mutation occurred in a gene which caused growth in a specific lobe of the brain responsible for verbal communication, and coincided with language development in the species.
And even further back in history, a prior mutation occurred which gave growth to a different lobe of the brain which controls artistic expression and coincided with the appearance of cave paintings.
