Measuring the Sensitivity of Single-locus


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Measuring the Sensitivity of Single locus Neutrality Tests Using a Direct Perturbation Approach Daniel Garrigan Richard Lewontin and John Wakeley Department of Organismic and Evolutionary Biology Harvard University Corresponding author E mail daniel garrigan rochester edu Present address Department of Biology University of Rochester Associate editor John H McDonald Abstract Key words DNA sequence infinite allele model infinite sites model natural selection polymorphism Introduction A major question pertinent to understanding the genetic variation within and between species is how important natural selection has been in determining that variation That is how much of the observed genetic differentiation is a consequence of direct physiological developmental and behavioral causal relations between DNA sequence variation and variation in fertility and probability of survival of individuals carrying these sequences The obvious direct approach to this problem would be to measure the components of reproductive fitness in different genotypes but there are a number of serious limitations inherent in this approach especially for animals Orr 2009 First it is extremely difficult if not impossible to obtain complete fitness components including probabilities of different matings fertility schedules and life tables for organisms whose life cycle cannot be observed in detail under natural conditions Second even if complete life cycle components can be obtained large enough sample sizes to detect selection are not possible unless fitness effects are drastic e g see the study by Christiansen and Frydenberg 1973 of an esterase polymorphism in the live bearing fish Zoarces viviparus where all the components of fitness could be measured Third measures of fitness components in present day environments may not necessarily reflect fitness in past environments One solution offered to circumvent these difficulties has been to attempt to infer the occurrence of natural selection from extant

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