One of the issues scientists run into when doing selective breeding is running out of variation to select on. In the early part of the 20th century they discovered that it was possible to create variation in plants through induced mutagenesis. Induced mutagenesis changes plant DNA by exposing plants to X-rays, gamma rays, or mutagenic chemicals. This process leads to random mutations in the plant which are later screened for novel traits which may be desirable. These traits can later be selected for and the mutagenised plants can be further crossed in breeding programmes. This approach is quite random and can also create detrimental mutations along with positive mutations, and works on the shotgun approach by making hundreds of mutations and hoping you get a hit (positive mutation). This approach, however is largely unregulated due to its history of safe use.