Levitan D R, Grosberg R K
Center for Population Biology, University of California, Davis 95616.
Mol Ecol. 1993 Oct;2(5):315-26. doi: 10.1111/j.1365-294x.1993.tb00024.x.
For organisms in which direct observation of mating and subsequent dispersal of offspring and relatives is impossible, patterns of reproductive success and genealogical relationship can only be established using genetic markers. The ideal genetic assay would (1) employ highly polymorphic genetic markers for distinguishing among individuals; (2) use little tissue for analysing early life-history stages; and (3) require minimal investment in time and money for population level studies. From this perspective, DNA polymorphisms revealed by PCR amplification using random ten-base primers [Randomly Amplified Polymorphic DNA (PCR-RAPD) or Arbitrarily Primed DNA (AP-PCR)] have great potential. However, the evidence that RAPD/AP markers are both heritable and can be repeatably amplified remains controversial. This study characterizes patterns of inheritance and polymorphism of RAPD markers in the free-spawning, colonial marine hydrozoan Hydractinia symbiolongicarpus. In all cases, the amplification products were identical among extractions from the same clone. Of 56 primers screened, 13 had sufficient polymorphism and scoreability for an analysis of parentage and higher-order genetic relationships in three matings. These primers generated 156 unique amplification products (putative loci), of which 133 were polymorphic. All but four of these loci were inherited as dominant mendelian markers. Our study suggests that the presence of a marker represents a single allele at a locus; however, what appear to be single null alleles may actually comprise several segregating alleles. When the identity of neither parent was known a priori, inclusion (unique markers present in offspring and only one of the potential parents) proved to be more efficient than exclusion for assigning offspring to parents. The most powerful approach, however, was cluster analysis of all presence/absence information for the marker bands. Clustering avoided the pitfalls caused by the appearance of occasional nonparental bands, and constructed a hierarchical framework that correctly reflected all genealogical relationships.
对于那些无法直接观察交配以及后代和亲属随后扩散情况的生物，只能使用遗传标记来确定繁殖成功模式和谱系关系。理想的遗传分析方法应具备以下几点：（1）采用高度多态性的遗传标记来区分个体；（2）只需少量组织就能分析生命史早期阶段；（3）在群体水平研究中所需的时间和资金投入最少。从这个角度来看，利用随机十碱基引物进行PCR扩增所揭示的DNA多态性[随机扩增多态性DNA（PCR-RAPD）或任意引物DNA（AP-PCR）]具有很大潜力。然而，RAPD/AP标记具有遗传性且能被重复扩增这一证据仍存在争议。本研究对自由产卵的群体海洋水螅虫共生长柄水螅（Hydractinia symbiolongicarpus）中RAPD标记的遗传模式和多态性进行了表征。在所有情况下，同一克隆提取物中的扩增产物都是相同的。在筛选的56种引物中，有13种具有足够的多态性和可评分性，可用于分析三次交配中的亲子关系和高阶遗传关系。这些引物产生了156个独特的扩增产物（假定位点），其中133个是多态性的。除了四个位点外，所有这些位点都作为显性孟德尔标记遗传。我们的研究表明，一个标记的存在代表一个位点上的单个等位基因；然而，看似单个无效等位基因实际上可能包含几个分离的等位基因。当事先不知道双亲的身份时，包含法（后代和仅一个潜在亲本中存在的独特标记）在将后代分配给亲本方面被证明比排除法更有效。然而，最有效的方法是对标记带的所有存在/缺失信息进行聚类分析。聚类避免了偶尔出现的非亲本带所导致的陷阱，并构建了一个正确反映所有谱系关系的层次框架。
