The relationship between the concepts of genetic diversity and differentiation

Summary Diversity as a measure of individual variation within a population is widely agreed to reflect the number of different types in the population, taking into account their frequencies. In contrast, differentiation measures variation between two or more populations, demes or subpopulations. As such, it is based on the relative frequencies of types within these subpopulations and, ideally, measures the average distance of subpopulations from their respective lumped remainders. This concept of subpopulation differentiation can be applied consistently to a single population by regarding each individual as a deme (subpopulation) of its own, and it results in a measure of population differentiation _T which depends on the relative frequencies of the types and the population size. _T corresponds to several indices of variation frequently applied in population genetics and ecology, and it verifies these indices as measures of differentiation rather than diversity. For any particular frequency distribution of types, the diversity is then shown to be the size of a hypothetical population in which each type is represented exactly once, i. e. for which _T =1. Hence, the diversity of a population is its differentiation effective number of types. This uniquely specifies the link between the two concepts. Moreover, again corresponds to known measures of diversity applied in population genetics and ecology. While population differentiation can always be estimated from samples, the diversity of a population, particularly if it is large, may not be. In such cases, it is recommended that population differentiation is estimated and the corresponding sample diversity merely computed. Finally, a solution to the problem of measuring multi-locus diversities is provided.     

Transferability of Cucurbita SSR markers for genetic diversity assessment of Turkish bottle gourd (Lagenaria siceraria) genetic resources

The genetic diversity present in crop landraces represents a valuable genetic resource for breeding and genetic studies. Bottle gourd (Lagenaria siceraria) landraces in Turkey are highly genetically diverse. However, the limited genomic resources available for this crop hinder the molecular characterization of Turkish bottle gourd germplasm for its adequate conservation and management. Therefore, we evaluated the efficacy of 40 SSR markers from major cucurbit crops (Cucurbita pepo L. and Cucurbita moschata L.) in 30 bottle gourd landraces, together with 16 SRAP primer combinations. In addition, we compared the genetic relationship between bottle gourd and 31 other cucurbit accessions (11 Cucurbita maxima, 3 C. moschata, 5 C. pepo subsp. ovifera, 10 C. pepo and 2 Luffa cylindrica). Twenty-seven Cucurbita SSR markers showed transferability to bottle gourd. SSR markers amplified 59 alleles, in bottle gourd genome with an average of 1.64 alleles per locus. Together, SSR and SRAP markers amplified 453 fragments across the 61 accessions, and clearly discriminated L. siceraria and L. cylindrica from the other cucurbit species. Genetic diversity analysis separated edible cucurbit from ornamentals, while population structure analysis classified L. siceraria in two subpopulations defined by fruit shape, rather than geographical origin. The results indicated that the genomic resources available for Cucurbita species are valuable to study and preserve the genetic diversity of bottle gourd in Turkey.     

孑遗植物银杏群体遗传多样性的ISSR分析

采用ISSR分子标记技术,对江苏泰兴、美国纽约的栽培银杏(Ginkgo biloba)群体和中国3个可能为野生的银杏自然群体(浙江西天目山、贵州务川、湖北大洪山区)的遗传多样性水平和群体遗传结构进行了研究。用13个引物对5个群体共66个样品进行扩增,共得到88个清晰的扩增位点,其中多态性位点62个,多态位点百分率(PPB)为70．45％。POPGENE分析结果表明：与其他裸子植物相比,银杏具有丰富的遗传变异(He=0．2408;Ho=0．3599)。贵州务川群体的遗传多样性水平最高(PPB=56．82％,He=0．2089,Ho=0．3087),江苏泰兴栽培群体(PPB=34．09％,,Ho=0．1269,Ho=0．1858)和美国纽约的栽培群体(PPB=23．86％,,He=0．0884,Ho=0．1312)的遗传多样性水平较低。Nei′s遗传多样性分析和AMOVA分析表明,3个可能的自然群体间出现了一定程度的遗传分化(Gst=0．1476,Φst=14．26％)。群体间一定程度的遗传分化可能是人为选择压力和基因流障碍引起的。根据Nei′s遗传距离矩阵分别构建了群体间和个体间的遗传关系树状图。由UPGMA聚类分析可知,贵州务川群体与浙江西天目山群体优先聚类;美国纽约群体与湖北大洪山群体具有较近的亲缘关系,它们可能为同一野生群体的后裔。通过对银杏群体遗传结构的分析并结合群落学调查研究,结果表明：贵州务川银杏群体很可能为野生自然群体。基于银杏群体遗传学和生态学的研究结果,建议在自然银杏群体最适生境和遗传多样性最高的贵州务川建立银杏保护区。由于银杏群体间出现了一定程度的分化,建议3个自然群体间可进行植株和幼苗相互移栽,以提高群体间的基因交流,以最大限度地保护银杏的遗传多样性。     

Development of Ty1-copia retrotransposon-based SSAP molecular markers for the study of genetic diversity in peach

Sequence-specific amplified polymorphism (SSAP) technology is a novel, anchored PCR approach derived from AFLP, which amplifies the region between a transposon insertion and an adjacent restriction site and have higher levels of polymorphism. In the current study, we developed 16 SSAP markers based on the long terminal repeat (LTR) sequences of Ty1-copia retrotransposons in the peach and used them for DNA profiling of 52 individual peaches: 44 peach cultivars and 8 ornamental peaches. These primer combinations produced a total of 1,553 fragments and 1,517 polymorphic bands with a polymorphism percentage of 97.7%. Furthermore, the Shannon's information index of each primer combination ranged from 0.1593 to 0.4456. Neighbor-joining analyses revealed two main genetic clusters, corresponding to the fruit flesh types: (A-1) MF (melting flesh) with clingstone and ornamental peaches; (A-2) MF with freestone and NMF (non-melting flesh) with clingstone. Finally, cluster analyses revealed that all ornamental peaches are closely related to the MF with clingstone peach cultivars. The application of these primer combinations identified using SSAP will facilitate future cultivar identification and germplasm management in peaches.     

Advances in the development of molecular genetic tools for Mycobacterium tuberculosis

Mycobacterium tuberculosis, a Gram-positive bacterium of great clinical relevance, is a lethal pathogen owing to its complex physiological characteristics and development of drug resistance. Several molecular genetic tools have been developed in the past few decades to study this microorganism. These tools have been instrumental in understanding how M. tuberculosis became a successful pathogen. Advanced molecular genetic tools have played a significant role in exploring the complex pathways involved in M. tuberculosis pathogenesis. Here, we review various molecular genetic tools used in the study of M. tuberculosis. Further, we discuss the applications of clustered regularly interspaced short palindromic repeat interference (CRISPRi), a novel technology recently applied in M. tuberculosis research to study target gene functions. Finally, prospective outcomes of the applications of molecular techniques in the field of M. tuberculosis genetic research are also discussed.     

Analysis of the genetic diversity and population structure of Perinereis aibuhitensis in China using TRAP and AFLP markers

Perinereis aibuhitensis is found in the coastal waters of northwestern Pacific. Different ecotypes are distributed throughout the coastal sea beach based on their ecology and behavior, but relatively little is known about the population structure of this species. In this study, we estimated the genetic relationships within P. aibuhitensis using Target Region Amplified Polymorphisms (TRAP) and Amplified Fragment Length Polymorphisms (AFLP) that were derived from related populations on the coasts of China. All populations were uniquely fingerprinted using the TRAP and AFLP marker method. The mean genetic distance was estimated to be 0.1859 based on the TRAPs and AFLPs. Using the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) by Molecular Evolutionary Genetics Analysis (MEGA) 6.06 software, Principal Coordinate Analysis (PCA) and STRUCTURE analysis, the phylogenetic tree of the ten P. aibuhitensis populations was separated into four major clusters; however, the mantel test indicated that there was no significant correlation between the genetic and geographical distances due to gene differentiation and gene flow (P > 0.005). The genetic diversity was low for P. aibuhitensis at the population level compared with the species level. Finally, an appropriate strategy for conserving the P. aibuhitensis germplasm is proposed.     

Minimum population size,genetic diversity,and social structure of the Asian elephant in Cat Tien National Park and its adjoining areas,Vietnam, based on molecular genetic analyses

Vietnam’s elephant population that has suffered severe declines during the past three decades is now believed to number 60–80 individuals in the wild. Cat Tien National Park is thought to be one of the key areas for the recovery of Vietnam’s elephants. We carried out a molecular genetic study of elephants in Cat Tien National Park and its adjoining areas with the objectives of estimating minimum population size, assessing genetic diversity, and obtaining insights into social organization. We obtained a minimum population size of 11 elephants based on a combination of unique nuclear microsatellite genotypes and mitochondrial haplotypes. While mitochondrial diversity based on a 600-base pair segment was high in this small sample of individuals, the six microsatellite loci examined showed low diversity and the signature of a recent population bottleneck. Along with nuclear genetic depauperation of Cat Tien’s elephants, we also report disruption of normal social organization, with different matrilines having coalesced into a single social group because of anthropogenic disturbance. The results emphasize the critical condition of this elephant population and the need for urgent conservation measures if this population is to be saved.     

The blacks of Panama: their genetic diversity as assessed by 15 inherited biochemical systems

Panama's black citizens are culturally and historically divisible into two groups, the Spanish-speaking coloniales and the English-speaking anglos or afro-antillanos. Until recently these groups have been geographically as well as culturally isolated one from the other, although both are predominantly of West and Southwest African origin. Assessment of the genetic diversity within-villages and within language groups reveals as much, possibly somewhat more, diversity in 15 inherited biochemical markers within villages and language groups as that which obtains between villages and language groups. A number of rare variants at the 6-phosphogluconate dehydrogenase, lactate dehydrogenase, and esterase D loci were encountered and are described.     

Isolation and characterization of microsatellite loci for the analysis of genetic diversity in Whitmania pigra

The objective of this study was to isolate microsatellite loci to analyze the genetic diversity of Whitmania pigra. Four new microsatellite markers of W. pigra were developed from an enriched library and ten from a modified SAMPL assay. A total of 127 alleles were detected, with an average of 9.1 alleles per locus. The expected heterozygosity (He) of each microsatellite locus varied from 0.451 to 0.857, with an average of 0.688. The polymorphism information content (PIC) of each microsatellite locus ranged from 0.361 to 0.838, with an average of 0.640. Analysis of molecular variance showed that the main variation component existed within the populations (81.64%) rather than among the populations (18.36%). Phylogenetic tree for 15 populations of Hirudo using the NJ method by MEGA 5.1 software were divided into two major clusters. These microsatellite markers will contribute to research on the individual identification, genetic diversity, population structure, genome mapping and conservation biology of Hirudo.     

The importance of control populations for the identification and management of genetic diversity

A fundamental criterion for recognizing species or populations as potentially endangered is the presence/absence of genetic diversity. However, the lack of control populations in many studies of natural systems deprives one from unambiguous criteria for evaluating the genetic effects of small population size and its potential effects on fitness. In this study, I present an example of how the lack of adequate controls may lead to erroneous conclusions for understanding the role that population size may play in the preservation of genetic diversity and fitness of natural populations. The genetic analysis of a population of greater prairie chickens from Illinois, USA, between two time periods (1974–1987 and 1988–1993) in which the studied population experienced a substantial reduction in size and fitness showed no apparent associations between population size and genetic diversity. However, genetic analysis of museum specimens from early this century indicated that Illinois prairie chickens had originally higher levels of genetic diversity, which suggest the Illinois population was already bottlenecked by the 1970s. This study emphasizes the importance of using historical controls to evaluate the temporal dynamics of genetic variability in natural populations. The large number of museum collections worldwide may provide a valuable source of genetic information from past populations, particularly in species currently endangered as a result of human activities. This revised version was published online in July 2006 with corrections to the Cover Date.     

AFLP analysis of the genetic diversity of Meloidogyne chitwoodi and M. fallax, major agricultural pests

M. chitwoodi and M. fallax populations are clustered and separated from the other species studied. The genetic diversity observed for M. incognita, M. arenaria, M. javanica, M. hapla, and M. mayaguensis correlates well with the previously validated species. Two main groups can be identified within the M. chitwoodi/M. fallax cluster, the first group comprises only M. chitwoodi populations whereas the second group is made of M. chitwoodi and M. fallax populations. Moreover, M. chitwoodi displays a higher genetic diversity than M. fallax and is characterised by the presence of several clusters.     

Phylogeography and genetic diversity of the red squirrel (Sciurus vulgaris) in China: Implications for the species' postglacial expansion history

The geographical distribution of Sciurus vulgaris spans much of the Palearctic from western Europe and the UK eastward to the pacific coast of East Asia. S. vulgaris occurs in China only in the far northwest and the northeast. Understanding of the species’ postglacial expansion history in East Asia has been limited by the paucity of molecular data. In this study, we used partial D-loop and cytochrome b gene sequences to assess mitochondrial DNA variation in S. vulgaris in China. Our objectives were to (1) determine phylogeographical patterns of S. vulgaris in China; (2) understand the species’ postglacial expansion history in this region; and (3) quantify genetic diversity levels within S. vulgaris populations in China. We identified a supported phylogenetic group in S. vulgaris from China, and found no tendency for haplotypes to cluster by geographic region. Our analysis of S. vulgaris from China and other regions supports the hypothesis that the Calabria region of southern Italy is a glacial refugium for the species. We tentatively propose a postglacial expansion pattern for the squirrels: migrating from Calabria via Central and Eastern Europe to Russia and from there to China, and firstly to the northwest and then to northeast in China. We found high levels of genetic diversity in S. vulgaris populations across China as a whole, and discussed its influential factors.     

EST-derived single nucleotide polymorphism markers for assembling genetic and physical maps of the barley genome

In a panel of seven genotypes, 437 expressed sequence tag (EST)-derived DNA fragments were sequenced. Single nucleotide polymorphisms (SNPs) that were polymorphic between the parents of three mapping populations were mapped by heteroduplex analysis and a genome-wide consensus map comprising 216 EST-derived SNPs and 4 InDel (insertion/deletion) markers was constructed. The average frequency of SNPs amounted to 1/130 bp and 1/107.8 bp for a set of randomly selected and a set of mapped ESTs, respectively. The calculated nucleotide diversities (π) ranged from 0 to 40.0 × 10⁻³ (average 3.1 × 10⁻³) and 0.52 × 10⁻³ to 39.51 × 10^–3 (average 4.37 × 10⁻³) for random and mapped ESTs, respectively. The polymorphism information content value for mapped SNPs ranged from 0.24 to 0.50 with an average of 0.34. As expected, combination of SNPs present in an amplicon (haplotype) exhibited a higher information content ranging from 0.24 to 0.85 with an average of 0.50. Cleaved amplified polymorphic sequence assays (including InDels) were designed for a total of 87 (39.5%) SNP markers. The high abundance of SNPs in the barley genome provides avenues for the systematic development of saturated genetic maps and their integration with physical maps. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Both R. Kota and R.K. Varshney contributed equally to this work.     

An estimation of the minimum number of SSR loci needed to reveal genetic relationships in wheat varieties: Information from 96 random accessions with maximized genetic diversity

Genetic relationships among common wheat varieties from the 10 wheat growing regions of China were assessed using SSR markers. The wheat varieties included 33 modern varieties and 63 landraces selected from the national gene bank collection of China. One hundred and four pairs of selected primers detected a total of 802 alleles, of which 234 were specific to A genome, 309 to B genome, and 221 to D genome. The average genetic richness per locus (A _ij /loci) for A, B and D genomes were 6.88, 7.92 and 7.62, respectively. Their average genetic dispersion indices (H _t ) were 0.637, 0.694 and 0.656, respectively. The B genome showed the highest genetic diversity among the three wheat genomes. The landraces had a higher genetic diversity than the modern varieties, and the major difference between the landraces and the modern varieties in China existed in the D genome, followed by B and A genomes. The majority of the accessions (65.6%) had heterogeneity at the 112 loci detected. The highest heterogeneity locus percentages were 9.09 and 12.73 in the modern varieties and the landraces, respectively. SSR data were analyzed with NTSYS-pc software. The genetic similarities between accessions were estimated with the DICE coefficient. The accessions clustered into two groups, the modern varieties and the landraces by the un-weighted pair-group method using arithmetic average (UPGMA). The trend of correlation coefficients between genetic similarity matrices based on different numbers of random alleles and that of 802 alleles showed that 550 alleles were sufficient to construct a robust dendrogram. The separated simulations from six sub-samples revealed that 550 alleles were the minimum number required to confidently determine the genetic relationships. It was shown that the number of alleles (loci) needed do not have a strong association with the number of wheat lines in the sample size. These data suggested that 73 loci with good polymorphism are needed to reflect genetic relationships among accessions with more than 90% certainty. In the dendrogram, most accessions from the same wheat region were clustered together, and those from geographically adjacent regions usually appeared in the same small group. This indicated that genetic diversity of Chinese common wheat has a close association with their geographic distribution and ecological environment.     

The use of microsatellite markers for detection of genetic diversity in barley populations

 A barley lambda-phage library was screened with (GA)n and (GT)n probes for developing microsatellite markers. The number of repeats ranged from 2 to 58 for GA and from 2 to 24 for GT. Fifteen selected microsatellite markers were highly polymorphic for barley. These microsatellite markers were used to estimate the genetic diversity among 163 barley genotypes chosen from the collection of the IPK Genebank, Germany. A total of 130 alleles were detected by 15 barley microsatellite markers. The number of alleles per microsatellite marker varied from 5 to 15. On average 8.6 alleles per locus were observed. Except for GMS004 all other barley microsatellite markers showed on average a high value of gene diversity ranging from 0.64 to 0.88. The mean value of gene diversity in the wild forms and landraces was 0.74, and even among the cultivars the gene diversity ranged from 0.30 to 0.86 with a mean of 0.72. No significant differences in polymorphism were detected by the GA and GT microsatellite markers. The estimated genetic distances revealed by the microsatellite markers were, on average , 0.75 for the wild forms, 0.72 for landraces and 0.70 among cultivars. The microsatellite markers were able to distinguish between different barley genotypes. The high degree of polymorphisms of microsatellite markers allows a rapid and efficient identification of barley genotypes. Received: 26 November 1997 / Accepted: 19 January 1998     

The use of RAPD markers for detecting genetic diversity,relationship and molecular identification of Chinese elite tea genetic resources [<Emphasis Type="Italic">Camellia sinensis</Emphasis> (L.) O. Kuntze] preserved in a tea germplasm repository

The genetic diversity, relationship and molecular identification of 15 well known, widely planted traditional Chinese elite tea genetic resources [Camellia sinensis (L.) O. Kuntze] preserved in the China National Germplasm Hangzhou Tea Repository in the Tea Research Institute of the Chinese Academy of Agricultural Sciences located in Zhejiang province, China, were investigated using RAPD markers. A total of 1050 bands with an average of 52.5 bands per primer, 70 bands per genetic resource were generated by the 20 selected primers from the 15 tea genetic resources. In the total of 137 amplified products, 129 were polymorphic, corresponding to 94.2% genetic diversity. The relative frequency of polymorphic products was from 0.24 to 0.83, with an average of 0.47. In general, this average frequency was relatively high. The genetic distances among the genetic resources were from 0.16 to 0.62, with an average of 0.37. The 15 tea genetic resources were grouped into three groups by UPGMA cluster analysis based on RAPD data. By using the presence of 20 unique RAPD markers and the absence of 11 unique markers, all the 15 investigated tea genetic resources could be easily identified. RAPD markers provided a practical method not only to evaluate the genetic diversity and relationship, but also to identify tea genetic resources.