Amelioration of Horizontally Transferred Genes

Licentiate thesis, 2008

The importance of Horizontal (Lateral) Gene Transfer has attracted much attention during the last few decades. It is a very important factor in bacterial evolution and ecology, and it has great implications on human life as well. In response to selective and mutational pressures, horizontally transferred genes will undergo changes in DNA composition, ameliorate. When subject to these pressures long enough, the genes will exhibit a pattern of GC content, codon usage, and oligonucleotide abundance characteristic to the environment. The mechanisms responsible are not known, but it is commonly assumed that they result from processes specific to the host. In this dissertation I demonstrate that * a method used by Lawrence and Ochman in 1997 to estimate the time since the introduction of horizontally transferred genes is overly optimistic. I have developed a better technique for this purpose. * the mechanisms responsible for the amelioration of horizontally transferred genes can be attributed to the replicator molecule on which it is situated, be it the bacterial chromosome or a plasmid.