Abstract
Several seemingly unrelated phenomena-sterility, chromosome breakage, mutability, male recombination, and distorted segregation ratios-have been discovered independently by several investigators. They all have three striking properties: (1) The effects are confined to cells in the germ line; (2) they appear in hybrids between two strains, arbitrarily designated M and P; and (3) reciprocal matings differ, the effects appearing only when M females are mated to P males. The suggestion that these have a common etiology was first made by Kidwell, Kidwell, and Sved (1977), who also suggested that the syndrome be named "hybrid dysgenesis". This is now known to be caused by a transposable element, the P factor. The first suggestion that such an element is involved was made by Green (1977).<br> I will discuss especially the research of my colleagues, William Engels, Christine Preston, and Michael Simmons, but I will mention work done by many others. The very rapid progress in understanding the P factor has been made possible by the friendly cooperation and exchange of materials among several laboratories. This report is necessarily abbreviated. For those who would like to know more there is a recent review (Engels 1983), which contains much additional information and many references.
