Many experimental observations convincingly demonstrate that the genes and genome as a whole are sensitive to the magnetic fields, permanent and oscillating. The invasion of nuclear magnetic stable isotopes of Mg, Ca, and Zn in enzymatic catalysis disclosed new features of the DNA and gene chemistry; it discovered a new, radical pair mechanism, which substantiated the origin of magnetic effects. This mechanism implies electron transfer between the reaction partners; it is switched on by catalyzing ions and generates magneto-sensitive radical pairs. The key processes of gene functioning – DNA synthesis, DNA damage, and DNA repair – are shown to be magnetically controlled. A new anti-cancer strategy is suggested based on the using of the nuclear magnetic ions of magnesium, calcium, and zinc as a powerful and universal means to selectively kill only cancer cells; they are supposed to be highly promising for medical applications.