Hybrid vigor

Hybrid dysgenesis is a phenomenon observed in certain species of Drosophila, a genus of small flies, often called fruit flies. This phenomenon is characterized by a high rate of various genetic abnormalities, including mutations, chromosome rearrangements, and sterility. These abnormalities are observed in the offspring of certain crosses between strains of Drosophila, hence the term "hybrid" dysgenesis.

Mechanism

The mechanism of hybrid dysgenesis involves the mobilization of transposable elements, which are segments of DNA that can move around to different positions within the genome of a single cell. In the case of hybrid dysgenesis, these transposable elements become active in the germ line cells of the hybrid offspring, leading to a high rate of genetic abnormalities.

There are several types of hybrid dysgenesis in Drosophila, each associated with a different type of transposable element. These include the P-M system, the I-R system, and the hobo-Activator system. In each of these systems, one strain of Drosophila (the "inducer" strain) carries active transposable elements, while the other strain (the "reactive" strain) does not.

P-M System

The P-M system of hybrid dysgenesis is the most well-studied. It involves a transposable element called the P element. The P element is a type of DNA transposon, which means it moves around the genome by a "cut and paste" mechanism. In the P-M system, the inducer strain carries active P elements, while the reactive strain does not.

I-R System

The I-R system of hybrid dysgenesis involves a transposable element called the I element. Like the P element, the I element is a DNA transposon. In the I-R system, the inducer strain carries active I elements, while the reactive strain does not.

Hobo-Activator System

The hobo-Activator system of hybrid dysgenesis involves two types of transposable elements: the hobo element and the Activator element. Both of these elements are DNA transposons. In the hobo-Activator system, the inducer strain carries active hobo and Activator elements, while the reactive strain does not.

Implications

The phenomenon of hybrid dysgenesis has important implications for our understanding of genetic variation and evolution. It shows that transposable elements can have a major impact on the genetic makeup of a population, and that this impact can be influenced by the mating patterns within the population.