The Selfish Gene: The Extended Phenotype Of A Parasite

According to Dawkins mentioned in The Selfish Gene, the extended phenotype of a parasite is that selfish genes effect on not only the morphology of organisms but also the environment where they inhabit. There are three kinds of extended phenotype. Firstly, animals modify their environment by using architectural constructions. The classic example is that birds build nests, a shelter to live in. Same as human being build house to prevent extreme weather and ferocious carnivore. The second kind is that the behavior and appearance of host cells have advantage to both the host gene and the viral genes that infect the host. Viral gene is influencing other organism. For example, rabies virus can travel to host central nerve system via peripheral

A virus particle attaches and injects viral genome into host cell. Then the viral genome takes over the cell and recruit the host’s enzyme, and cellular enzyme start making new virus particles. The newly synthesized virus particle come together to form a new virus. Most of the virus infections lead to death of host cell, including apoptosis and cell lysis. When virus genes are more invasive, host cells undergo the infection process that mentioned above. Host cells replicate viral genome and help virus proliferate, once viral particles reassembly together On the other side, while the host genes are more aggressive, human immune system is activated and cause infected cell apoptosis. Both of these two situation cause a nonzero sum game, since it is either host cell dies or virus dies. However, there is a mechanism for virus dormant in the cell and cause no apparent effect on host cell called latency stage. Latency stage is a restrained form of viral genes, cells show few infectious symptoms and work normally. When viral gene is in latent noninfectious form, it escapes from immune system by several methods, such as down-regulate MHC molecule that presented on infected cell surface so that T cell cannot recognize it. In this case, because there is no harm for both host gene and virus gene, it is a zero