Exchange of Genetic Material
The Give and TakeWhen a parasitic relationship takes place, the parasite essentially becomes a part of the host. Though we typically think of parasites as organisms that steal nutrients from the host and give nothing in return, they sometimes share something valuable with their host. Though not common, parasites can exchange genetic information with their host, integrating their genes and forming a recombinant genome. This can be thought of as a form of horizontal gene transfer, where genes are exchanged between lineages (non-sexually) rather than within a lineage (sexually).1
How Does This Happen?
Rafflesia cantleyi (red flower) attached to it's host
Tetrastigma rafflesiae. 
|The lytic and lysogenic cycle of bacteriophages which transfers genetic information from cell to cell. |
Why does it happen?