Population Biology of the psr Chromosome

近年来，人们对某些遗传因素可能是“自私的”或“寄生的”这一概念越来越感兴趣，即它们可能除了自身在物种内的繁殖外没有其他功能。这里的研究涉及一种已知的最极端的寄生元素--海燕的PSR(父性比)染色体。PSR是正常传播的，但会导致父本染色体的丢失。由于在这种昆虫中，雄性通常是单倍体，雌性是二倍体，PSR的作用是通过完全破坏父亲的基因组，将二倍体雌性卵子转化为单倍体雄性卵子(携带PSR)。PSR从这种表型中获得了传播优势，因为它通过雄性的传播率很高，而通过雌性的传播率很低。这是研究寄生遗传元素进化的一个很好的系统。将进行研究以回答以下具体问题：(A)PSR在自然种群中的分布是什么？(B)种群结构如何影响PSR的频率？和(C)PSR染色体的起源是什么？这些问题是可以回答的，因为重组克隆可以用来表征染色体和进行种群研究。此外，还建立了PSR的实验室和田间群体遗传学研究程序。遗传学、细胞遗传学和分子研究将确定PSR染色体的结构。实地研究将确定PSR在北美3个近缘种的北美黄蜂种群中的分布。实验室种群实验将研究不同种群结构下的PSR种群动态。最后，将通过比较3种黄蜂的模式来确定PSR染色体上序列的可能来源。除了提供对“自私”DNA的遗传和进化的基本洞察外，PSR染色体还可以成为研究染色体印记的遗传基础的一个容易处理的系统。PSR还具有作为害虫生防剂的巨大潜力。

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.