"P" elements are commonly used as mutagenic agents in genetic experiments with "Drosophila." One advantage of this approach is that the mutations are easy to locate. In hybrid dysgenesis, one strain of "Drosophila" mates with another strain of "Drosophila" producing hybrid offspring and causing chromosomal damage known to be dysgenic. Hybrid dysgenesis requires a contribution from both parents. For example, in the "P-M" system, where the "P" strain contributes paternally and "M" strain contributes maternally, dysgenesis can occur. The reverse cross, with "M" cytotype father and "P" mother, produces normal offspring, as it crosses in a "P" x "P" or "M" x "M" manner. "P" male chromosomes can cause dysgenesis when crossed with an "M" female.