Evolution of P-Element Copy Number in Drosophila melanogaster

Transposable elements comprise a significant portion of the genomes of both plants and animals. The parasitic nature of transposable elements can modify genome structure, gene expression, and genome stability. Transposable elements are responsible for their negative impact due to their inherent tendency to insert themselves into the genome of the host organism and replicate itself throughout the genome. An example of a transposable element invasion is the invasion of the P-element transposon in D. melanogaster flies around 1950. D. melanogaster responded to the invasion via small RNAs known as piwi interacting RNA (piRNA). The piRNA pathway uses piRNAs that are transcribed in the germline in response to P-element copies located on piRNA clusters. The piRNA pathway evolved in D. melanogaster is a great model to study host tolerance and repression of transposable elements. Because the piRNA silencing pathways depends on P-element insertions into piRNA clusters, there should be a relationship between P-element copy number and evolution of the piRNA silencing pathway. As P-element copy number increases across successive generations, the probability of an insertion into a piRNA cluster should increase, which will lead to more production of piRNA and a more evolved piRNA silencing pathway. This relationship can be tested by examining the genome of experimental flies from successive generations for P-element copy numbers using relative standard qPCR.