Apportionment Of Genetic Diversity Research Articles

Echoes of the past: hereditarianism and A Troublesome Inheritance.

In 1969, Arthur Jensen ignited adecades-long debate when he wrote thatit is a ‘‘not unreasonable hypothesis thatgenetic factors are strongly implicated inthe average Negro–white intelligence dif-ference’’ [1]. From this he inferred thateducational interventions in communitieswhose members have lower measuredintelligence quotient (IQ) could not suc-ceed.The errors in Jensen’s choice of data [2]and statistical methods used to compute aheritability of about 80% for measured IQwere pointed out by numerous geneticistsand statisticians. 25 years after Jensen’sincendiary paper, Herrnstein and Mur-ray’s book, The Bell Curve [3], drewinferences similar to Jensen’s that differ-ences among races and social classes in IQwere genetically based. The Bell Curveelicited a flood of strong criticisms of thedata used, the statistical analyses, and thepolicy inferences [4]. Much of the criticismof Jensen and Herrnstein and Murraycenters on their interpretation of herita-bility of IQ. In 1975, Richard Lewontinand I [5] stressed the failure of theheritability statistic to do what theseauthors claim; namely, to show that IQis largely genetically determined andhence that traits related to IQ, such aseducational or economic success, would beimpervious to environmental intervention.As pointed out by Nicholas Wade inthe first half of A Troublesome Inheri-tance, we are now in a genomic age,where individual differences at the level ofDNA can be detected. The early chapterspresent a hodgepodge of historical ideasabout race, aggression, and genetics. Onpage 57, Wade gives an inkling of whatwill come in the last half of the book:‘‘important aspects of human social be-havior are shaped by the genes’’ and‘‘these behavior traits are likely to varyfrom one race to another, sometimessignificantly so’’ [6].Whereas inferences on the causes ofhuman behavioral variation referred toabove were based on correlations betweenrelatives, on pages 97–99 Wade developshis arguments for the genetic basis of socialbehaviors in the second half of A TroubledInheritance from results on worldwidevariation in DNA polymorphisms, namelymicrosatellite polymorphisms (The Rosen-berg-Feldman studies) [7,8] and singlenucleotide polymorphisms (another Stan-ford study) [9], from the Human GenomeDiversity Panel [10]. Here, as in hisprevious journalism about these studies,Wade exhibits a complete lack of under-standing of their implications. For exam-ple, he does not mention the finding,stressed in both studies, that only 5%–10%of the worldwide genomic variation isbetween continental groups, while the vastmajority is between individuals withinpopulations.Using data from 15 protein genes, R. C.Lewontin in 1972 [11] was the first topoint out that the overwhelming majorityof human genotypic variation is withinpopulations, and that continental ‘‘races’’differed little genetically. 25 years later,Barbujani et al. [12] came to the sameconclusion from their study of 109 DNAmarkers. Wade (page 120) criticizes Le-wontin’s conclusion that ‘‘racial classifica-tion is now seen to be of virtually nogenetic or taxonomic significance’’ asrepresenting Lewontin’s ‘‘political stakein the issue.’’From the data and analyses of world-wide molecular genomic variation, Rich-ard Lewontin and I amplified the conclu-sions of Lewontin and Barbujani et al. asfollows: ‘‘The repeated and consistentresults on the apportionment of geneticdiversity…show that the genes underlyingthe phenotypic differences used to assignrace categories are atypical of the genomein general and are not a reliable index tothe amount of genetic differentiationbetween groups. Thus, racial assignmentloses any general biological interest. Forthe human species, race assignment ofindividuals does not carry with it anygeneral implication about genetic differ-entiation’’ [13]. The increased resolutionon patterns of human variation that wenow have has enabled us to understand agreat deal about human migration, ad-mixture, population size, and naturalselection. However, it has not told us thatthe earlier studies underestimated thebiological reality of race.Even though the between-continentfraction of genetic variation is small, asthe reader discovers on leaving the firsthalf of A Troublesome Inheritance, Wade’serroneous interpretation of its significancefor racial differences becomes the basis for

Conservation Genetics of Remnant Lilium philadelphicum Populations in the Midwestern United States

In recent decades, an increasing number of plant species have been negatively affected by anthropogenic habitat fragmentation and disturbance. In many cases, the habitat matrix between populations has been converted from a natural to an urban environment. One such species, Lilium philadelphicum (Liliaceae) a showy perennial with a naturally patchy distribution, currently has populations in parts of its range in North America that persist on highly urbanized and fragmented landscapes. In this study, we used six nuclear microsatellite loci to characterize the amount and apportionment of genetic diversity among 12 remnant populations in the Midwest United States. Genetic diversity was high (7–31 alleles per locus, mean HO = 0.44–0.70). An analysis of molecular variance (AMOVA) detected a low level of genetic structure (FST = 0.06, P < 0.001), and no effect of isolation by distance among sites (r2 = 0.02, P = 0.28). Principle coordinate analysis (PCoA) of inter-individual genetic distances revealed essentially no structuring with PC axes one and two explaining only 22.5 and 19.7% of the observed variation respectively. Moreover, Bayesian exploration of population structure supported this observed lack of structure with a low optimum number of estimated genetic “clusters” (e.g., populations; K = 1). If habitat fragmentation does affect gene flow among populations we cannot yet detect a strong genetic signature of this process; most likely due to the recency of landscape disturbance relative to the long generation time of this species. These results suggest that the genetic composition of these remnant populations is relatively homogenous and as such, provides land managers with a large potential germplasm source with a broad genetic base for use in local restoration activities.

The impact of clonality on parasite population genetic structure

In this paper, we briefly review the consequences of clonal reproduction on the apportionment of genetic diversity in parasite populations. We distinguish three kinds of parasite lifecycle where clonal reproduction occurs. The consequences of this mode of reproduction for the different kinds of parasite life-cycles are described. We here particularly focus on clonal diploids.

Genetic Diversity in a Worldwide Collection of Cherimoya Cultivars

Genetic diversity of 206 cherimoya (Annona cherimola Mill.) cultivars representing the major regions of production was determined from an analysis of 23 isozyme loci. Gene diversity in cherimoya was high, although not equally distributed among countries. Peru and Ecuador, the countries of origin of this species, showed the greatest diversity, and Spain and Madeira (Portugal) showed the least, probably due to genetics bottlenecks resulting from limited introduction. Cultivars from California showed high values for several genetic diversity measures, likely due to their diverse origins. The expansion of cherimoya cultivation out the area of origin has produced a change in the apportionment of genetic diversity, with an increase in the inter-populational components, but likely without a general erosion overall.

Genetic and demographic dynamics of small populations of Silene latifolia.

Small local populations of Silene alba, a short-lived herbaceous plant, were sampled in 1994 and again in 1999. Sampling included estimates of population size and genetic diversity, as measured at six polymorphic allozyme loci. When averaged across populations, there was very little change between samples (about three generations) in population size, measures of within-population genetic diversity such as number of alleles or expected heterozygosity, or in the apportionment of genetic diversity within and among populations as measured by F(st). However, individual populations changed considerably, both in terms of numbers of individuals and genetic composition. Some populations doubled in size between samples, while others shrank by more than 75%. Similarly, expected heterozygosity and allele number increased by more than two-fold in individual populations and decreased by more than three-fold in others. When population-specific change in number and change in measures of genetic diversity were considered together, significant positive correlations were found between the demographic and genetic variables. It is speculated that some populations were released from the demographic consequences of inbreeding depression by gene flow.

Apportionment of global human genetic diversity based on craniometrics and skin color.

A number of analyses of classical genetic markers and DNA polymorphisms have shown that the majority of human genetic diversity exists within local populations (approximately 85%), with much less among local populations (approximately 5%) or between major geographic regions or "races" (approximately 10%). Previous analysis of craniometric variation (Relethford [1994] Am J Phys Anthropol 95:53-62) found that between 11-14% of global diversity exists among geographic regions, with the remaining diversity existing within regions. The methods used in this earlier paper are extended to a hierarchical partitioning of genetic diversity in quantitative traits, allowing for assessment of diversity among regions, among local populations within regions, and within local populations. These methods are applied to global data on craniometric variation (57 traits) and skin color. Multivariate analysis of craniometric variation shows results similar to those obtained from genetic markers and DNA polymorphisms: roughly 13% of the total diversity is among regions, 6% among local populations within regions, and 81% within local populations. This distribution is concordant with neutral genetic markers. Skin color shows the opposite pattern, with 88% of total variation among regions, 3% among local populations within regions, and 9% within local populations, a pattern shaped by natural selection. The apportionment of genetic diversity in skin color is atypical, and cannot be used for purposes of classification. If racial groups are based on skin color, it appears unlikely that other genetic and quantitative traits will show the same patterns of variation.

HIERARCHICAL ANALYSIS OF GENETIC POPULATION STRUCTURE IN THE NOISY MINER USING DNA MICROSATELLITE MARKERS

Abstract The Noisy Miner (Manorina melanocephala) is a common, cooperatively breeding meliphagid of eastern and southeastern Australia. We used DNA microsatellites to examine the apportionment of genetic diversity in Noisy Miners at disparate geographic scales to generate baseline information about the population genetic structure of this species. We examined five loci for 79 individuals from four populations. We found small amounts of genetic differentiation between paired populations separated by 30–40 km, and more substantial and significant differentiation between populations separated by more than 1000 km. This result implies substantial gene flow on local scales but much less at regional levels, probably reflecting short dispersal distances and isolation by distance. Analisis Jerarquico de la Estructura Genetica Poblacional de Manorina melanocephala Utilizando Marcadores de ADN Microsatelital Resumen. Manorina melanocephala es un melifagido comun del sur-este de Australia que presenta cria cooperati...

Allozyme diversity in endemic flowering plant species of the Juan Fernandez Archipelago, Chile: ecological and historical factors with implications for conservation

The level and apportionment of allozyme diversity were determined for 29 endemic (and 1 native) species from the Juan Fernández Islands, Chile. Mean diversities at the species level (H(es) = 0.065) are low but comparable to those measured for other insular endemics in the Pacific. A high mean proportion (0.338) of species-level diversity resides among populations. Diversity statistics were compared for species in different ecological-life history trait categories and abundance classes. Species occurring in large populations and those present in scattered small populations have higher diversities than species occurring in one or two populations. Although not significant with the conservative statistical test employed, lower diversity was found in highly selfing species as compared to animal- or wind-pollinated species. The apportionment of genetic diversity within and among populations (G(ST) values) is not significantly different for any of the species categories. Of particular interest is the lack of difference between animal- and wind-pollinated species because previous analyses of large data sets showed higher differentiation between populations of animal- than wind-pollinated species. Historical factors, both ecological and phylogenetic in nature, can influence the level and apportionment of diversity within insular endemics, and thus ecological correlates of diversity seen in many continental species may not apply to endemics. The results have several conservation implications. The preservation of large populations or several small populations is important for conserving diversity within species because when species are reduced to one or two populations, allozyme diversity is sharply reduced. High mean G(ST) values for the species examined illustrate the need for conserving as many populations as possible, either in the wild or in the garden, to preserve maximal diversity within species. Effective conservation strategies require empirical knowledge of each species.

Genetic Diversity in Liatris cylindracea

A genetically substructured population of the perennial, outbreeding herb, Liatris cylindracea was marked off into a grid with quadrat size that approximates the neighborhood size of Liatris. The plants were genotyped at 27 allozyme loci, 15 of which were polymorphic. The apportionment of genetic diversity within the population was determined by the Shannon information measure. Ninety-three percent of the total diversity is represented within each neighborhood. Five percent of the diversity is due to between neighborhoods, and about 2% is due to differences between sample rozs and columns. It is concluded that the subdivision of a population does not result in a loss of genetic diversity within neighborhoods. The properties of genetically subdivided populations have received considerable attention by theoreticians (e.g., Wright, 1943a; Kimura & Weiss, 1954; Maruyama, 1970). Because of the difficulty in the past of finding suitable single locus genetic markers, few experimental studies on genetic substructuring have been available. Now, with the advent of allozyme electrophoresis as a tool for the genetic analysis of natural populations, an increased number of studies on both animals (Selander 8c Yang, 1969; Workman gc Niswander, 1970; Neel gc Ward, 1972) and plants (Schaal, 1975) have indicated that populations of some organisms are genetically