Cell lines which are infected with retrovirus are resistant to superinfection by a related retrovirus. Packaging of whole virions within synthetic lipid vesicles allows efficient infection of such resistant cell lines. This system is more efficient in introducing encapsulated virus into infected cells than into uninfected cells.

We present an approximate analytic study of our previously introduced model of evolution including the effects of genetic exchange. This model is motivated by the process of bacterial transformation. We solve for the velocity, the rate of increase of fitness, as a function of the fixed population size, N. We find the velocity increases with ln N, eventually saturating at an N which depends on t...

March 2000 " Wildlife Bulletins frequently contain preliminary data, so conclusions based on these may be subject to change. Bulletins receive some review and may be cited in publications. Copies may be obtained, depending upon supply, from the Ministry of Environment, Lands and Parks,

John Karlsson is a researcher and farmer who has been working on a variety of sheep selection and resistance to parasites for more than 30 years. He is a Senior Veterinary Officer at the Department of Agriculture and Food Western Australia (DAFWA). At DAFWA he has worked on regulatory disease management programmes and providing general advice to livestock farmers since 1978. Al Karlsson is a Zo...