Population Biology of the psr Chromosome

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Within recent years there has been increasing interest in the concept that some genetic elements may be "selfish" or "parasitic", i.e. they may have no function other than their own propagation within a species. Research here concerns the most extreme example of a parasitic element known, the psr (paternal sex ratio) chromosome in Nasonia vitripennis. Psr is transmitted normally, but then causes loss of the paternal chromosomes. Because males are normally haploid and females diploid in this insect, the effect of psr is to convert diploid female eggs into haploid male eggs (which carry psr) by totally destroying the paternal genome. Psr gains a transmission advantage from this phenotype because it has a high transmission through males and a poor transmission through females. This is an excellent system for studying the evolution of parasitic genetic elements. Research will be undertaken to answer the following specific questions, (a) What is the distribution of psr in natural populations?, (b) How does population structure affect frequency of psr? and (c) What is the origin of the psr chromosome? These questions can be answered because recombinant clones can be used to characterize the chromosome and for population studies. In addition, procedures are established for population genetic studies of psr in both the laboratory and field. Genetic, cytogenetic and molecular studies will determine the structure of the psr chromosome. Field studies will determine the distribution of psr in North American wasp populations of 3 closely related Nasonia species. Laboratory population experiments will examine psr population dynamics under different population structures. Finally the possible origin of sequences on the psr chromosome will be determined by comparing patterns in the 3 wasp species. Besides providing basic insight into the genetics and evolution of "selfish " DNA, the psr chromosome could be a tractable system for studying the genetic basis of chromosome imprinting. Psr also has significant potential as a biological control agent of pest insects.