Proportion Of Loci Research Articles

Tetraploid interspecific hybrids between Asian and African rice species restore fertility depending on killer-protector loci for hybrid sterility.

Interspecific F1 hybrids between Asian (Oryza sativa) and African rice (Oryza glaberrima) exhibit severe sterility caused by the accumulation of hybrid sterility genes/loci at 15 or more loci. The mechanisms underlying the hybrid sterility genes are largely unknown; however, a few genes associated with the killer-protector system, which is the system most frequently associated with hybrid sterility genes, have been identified. We previously produced fertile plants as tetraploids derived from diploid interspecific F1 hybrids through anther culture; therefore, it was suggested that hybrid sterility could be overcome following tetraploidization. We investigated whether tetraploid interspecific plants produced by crossing are fertile and tested the involvement of hybrid sterility genes in the process. Fertile tetraploid interspecific F1 hybrid plants were obtained by crossing 2 tetraploids of O. sativa and O. glaberrima. To elucidate the relationships between pollen fertility and the hybrid sterility loci in the tetraploid F1 microspores, we performed genetic analyses of the tetraploid F2 hybrids and diploid plants obtained from the microspores of tetraploid interspecific hybrids by anther culture. The result suggested that the tetraploid interspecific hybrids overcame pollen and seed infertility based on the proportion of loci with the killer-protector system present in the tetraploids. The heterozygous hybrid sterility loci with the killer-protector system in the tetraploid segregate the homozygous killed allele (16.7-21.4%), with more than three-quarters of the gametes surviving. We theoretically and experimentally demonstrated that fertile rice progenies can be grown from tetraploid interspecific hybrids.

Comparing Likelihood Ratios to Understand Genome-Wide Variation in Phylogenetic Support.

Genomic data have only sometimes brought resolution to the tree of life. Large phylogenomic studies can reach conflicting conclusions about important relationships, with mutually exclusive hypotheses receiving strong support. Reconciling such differences requires a detailed understanding of how phylogenetic signal varies among data sets. Two complementary strategies for better understanding phylogenomic conflicts are to examine support on a locus-by-locus basis and use support values that capture a larger range of variation in phylogenetic information, such as likelihood ratios. Likelihood ratios can be calculated using either maximum or marginal likelihoods. Despite being conceptually similar, differences in how these ratios are calculated and interpreted have not been closely examined in phylogenomics. Here, we compare the behavior of maximum and marginal likelihood ratios when evaluating alternate resolutions of recalcitrant relationships among major squamate lineages. We find that these ratios are broadly correlated between loci, but the correlation is driven by extreme values. As a consequence, the proportion of loci that support a hypothesis can change depending on which ratio is used and whether smaller values are discarded. In addition, maximum likelihood ratios frequently exhibit identical support for alternate hypotheses, making conflict resolution a challenge. We find surprising support for a sister relationship between snakes and iguanians across four different phylogenomic data sets in contrast to previous empirical studies. [Bayes factors; likelihood ratios; marginal likelihood; maximum likelihood; phylogenomics; squamates.].

Widespread Allelic Heterogeneity in Complex Traits

Recent successes in genome-wide association studies (GWASs) make it possible to address important questions about the genetic architecture of complex traits, such as allele frequency and effect size. One lesser-known aspect of complex traits is the extent of allelic heterogeneity (AH) arising from multiple causal variants at a locus. We developed a computational method to infer the probability of AHand applied it to three GWASs and four expression quantitative trait loci (eQTL) datasets. We identified a total of 4,152 loci with strong evidence of AH. The proportion of all loci with identified AH is 4%-23% in eQTLs, 35% in GWASs of high-density lipoprotein (HDL), and 23% in GWASs of schizophrenia. For eQTLs, we observed a strong correlation between sample size and the proportion of loci with AH (R2 = 0.85, p = 2.2× 10-16), indicating that statistical power prevents identification of AH in other loci. Understanding the extent of AH may guide the development of new methods for fine mapping and association mapping of complex traits.

Heterozygosity level and its relationship with genetic variability mechanisms in beans

Heterozygosity is an extremely important resource in early breeding programs using autogamous plants because it is usually associated with the presence of genetic variability. Induced mutation and artificial hybridization can increase distinctly the proportion of loci in heterozygosis. This study aimed to compare segregating and mutant populations and relate the mechanisms used to generate variability with their respective heterozygosity levels tested. The treatments mutant populations (M2, M3, M4, M5, M6 and M7), segregating populations (F4, F5 and F6) and lines (BRS Perola and IPR Uirapuru) were evaluated by multivariate analysis and compared by orthogonal contrasts. The canonical discriminant analysis revealed which response variables contributed to differentiate the treatments assessed. All orthogonal contrasts involving the mutant populations showed significant differences, except the contrast between M2 vs. M3, M4, M5, M6, M7. The orthogonal contrast between the mutant and segregating populations denotes a significant variation in the interest in genetic breeding. The traits stem diameter (1.41) and number of legumes per plant (2.72) showed the highest canonical weight in this contrast. Conversely, number of grains per plant (-3.58) approached the mutant and segregating populations. No significant difference was observed in the linear comparison of means F5 vs. F6. The traits are fixed early in the segregant populations, unlike the mutant populations. Comparatively, induced mutation provides more loci in heterozygosis than artificial hybridization. Selection pressure should vary according to the variability creation mechanism used at the beginning of the breeding program.

Conservation genetics of the annual hemiparasitic plant Melampyrum sylvaticum (Orobanchaceae) in the UK and Scandinavia

Melampyrum sylvaticum is an endangered annual hemiparasitic plant that is found in only 19 small and isolated populations in the United Kingdom (UK). To evaluate the genetic consequences of this patchy distribution we compared levels of diversity, inbreeding and differentiation from ten populations from the UK with eight relatively large populations from Sweden and Norway where the species is more continuously distributed. We demonstrate that in both the UK and Scandinavia, the species is highly inbreeding (global F IS = 0.899). Levels of population differentiation were high (F’ST = 0.892) and significantly higher amongst UK populations (F’ST = 0.949) than Scandinavian populations (F’ST = 0.762; P < 0.01). The isolated populations in the UK have, on average, lower genetic diversity (allelic richness, proportion of loci that are polymorphic, gene diversity) than Scandinavian populations, and this diversity difference is associated with the smaller census size and population area of UK populations. From a conservation perspective, the naturally inbreeding nature of the species may buffer the species against immediate effects of inbreeding depression, but the markedly lower levels of genetic diversity in UK populations may represent a genetic constraint to evolutionary change. In addition, the high levels of population differentiation suggest that gene flow among populations will not be effective at replenishing lost variation. We thus recommend supporting in situ conservation management with ex situ populations and human-mediated seed dispersal among selected populations in the UK.

Population genetic evidence that basidiospores play an important role in the disease cycle of rice‐infecting populations of Rhizoctonia solani AG‐1 IA in Iran

The fungus Rhizoctonia solani AG‐1 IA causes sheath blight, one of the most important rice diseases worldwide. The first objective of this study was to analyse the genetic structure of R. solani AG‐1 IA populations from three locations in the Iranian Caspian Sea rice agroecosystem. Three population samples of R. solani AG‐1 IA isolates were obtained in 2006 from infected rice fields separated by 126–263 km. Each field was sampled twice during the season: at the early booting stage and 45 days later at the early mature grain stage. The genetic structure of these three populations was analysed using nine microsatellite loci. While the population genetic structure from Tonekabon and Amol indicated high gene flow, they were both differentiated from Rasht. The high gene flow between Tonekabon and Amol was probably due mainly to human‐mediated movement of infested seeds. The second objective was to determine the importance of recombination. All three populations exhibited a mixed reproductive mode, including both sexual and asexual reproduction. No inbreeding was detected, suggesting that the pathogen is random mating. The third objective was to determine if genetic structure within a field changes over the course of a growing season. A decrease in the proportion of admixed genotypes from the early to the late season was detected. There was also a significant (P = 0·002) increase in the proportion of loci under Hardy–Weinberg equilibrium. These two lines of evidence support the hypothesis that basidiospores can be a source of secondary inoculum.

Estimating ancestry and heterozygosity of hybrids using molecular markers

BackgroundHybridization, genetic mixture of distinct populations, gives rise to myriad recombinant genotypes. Characterizing the genomic composition of hybrids is critical for studies of hybrid zone dynamics, inheritance of traits, and consequences of hybridization for evolution and conservation. Hybrid genomes are often summarized either by an estimate of the proportion of alleles coming from each ancestral population or classification into discrete categories like F1, F2, backcross, or merely “hybrid” vs. “pure”. In most cases, it is not realistic to classify individuals into the restricted set of classes produced in the first two generations of admixture. However, the continuous ancestry index misses an important dimension of the genotype. Joint consideration of ancestry together with interclass heterozygosity (proportion of loci with alleles from both ancestral populations) captures all of the information in the discrete classification without the unrealistic assumption that only two generations of admixture have transpired.MethodsI describe a maximum likelihood method for joint estimation of ancestry and interclass heterozygosity. I present two worked examples illustrating the value of the approach for describing variation among hybrid populations and evaluating the validity of the assumption underlying discrete classification.ResultsNaively classifying natural hybrids into the standard six line cross categories can be misleading, and false classification can be a serious problem for datasets with few molecular markers. My analysis underscores previous work showing that many (50 or more) ancestry informative markers are needed to avoid erroneous classification.ConclusionAlthough classification of hybrids might often be misleading, valuable inferences can be obtained by focusing directly on distributions of ancestry and heterozygosity. Estimating and visualizing the joint distribution of ancestry and interclass heterozygosity is an effective way to compare the genetic structure of hybrid populations and these estimates can be used in classic quantitative genetic methods for assessing additive, dominant, and epistatic genetic effects on hybrid phenotypes and fitness. The methods are implemented in a freely available package “HIest” for the R statistical software ( http://cran.r-project.org/web/packages/HIest/index.html).

Outcrossing rate of Couratari multiflora (J.Smith) Eyma (Lecythidaceae), a low-density tropical tree species from a central Amazonian rainforest

A multilocus mixed-mating model was used to evaluate the mating system of a population of Couratari multiflora, an emergent tree species found in low densities (1 individual/10 ha) in lowland forests of central Amazonia. We surveyed and observed phenologically 41 trees in an area of 400 ha. From these, only four mother trees were analyzed here because few of them set fruits, which also suffered high predation. No difference was observed between the population multilocus outcrossing rate (t mp = 0.953 ± 0.040) and the average single locus rate (t sp = 0.968 ± 0.132). The four mother trees were highly outcrossed (t m ~ 1). Two out of five loci showed departures from the Hardy-Weinberg Equilibrium (HWE) expectations, and the same results occurred with the mixed-mating model. Besides the low number of trees analyzed, the proportion of loci in HWE suggests random mating in the population. However, the pollen pool was heterogeneous among families, probably due to both the small sample number and the flowering of trees at different times of the flowering season. Reproductive phenology of the population and the results presented here suggest, at least for part of the population, a long-distance pollen movement, around 1,000 m.

Detection of genetic integrity of conserved maize (Zea mays L.) germplasm in genebanks using SNP markers

Twenty maize landrace accessions regenerated and conserved in five maize genebanks were investigated for genetic integrity using 1,150 Single Nucleotide Polymorphisms (SNPs) and 235 SNP haplotypes. The genetic diversity of three accessions changed significantly in terms of the average number of alleles per locus. Ten out of twenty accessions had significantly different SNP allelic frequencies, either after regeneration or in the same accession held in different genebanks. The proportion of loci with significant changes in SNP allelic frequency was very low (37/1,150). Changes in the major allelic frequency (MAF) for the majority of SNP loci (60.2–75.2%) were less than 0.05. For SNP haplotypes, the genetic diversity of four accessions changed significantly in terms of average number of haplotype alleles and polymorphic information content (PIC) per locus. The proportion of SNP haplotype alleles lost in the later generations ranged between 0 and 22.6%, and at the same time 0–19.9% of the SNP haplotype alleles appeared in later generations, however, these were absent in the earlier generations. Dynamic changes in genetic integrity, in terms of presence and absence of genes (alleles), by both SNP and SNP haplotype analysis were detected during regeneration. A suboptimum number of ears harvested in one generation can be combined with those from another, repeated regeneration to capture the diversity of the previous generation. Use of molecular markers during regeneration of accessions can help in understanding the extent of genetic integrity of the maize accessions in ex situ genebanks and in recommending the best practice for maintaining the original genetic diversity of the genebank accessions.

Abstract 802: Minimal deleted regions and their clinical significances in oral squamous cell cacinomas

Abstract With improvements in technologies, DNA alterations on a genome-wide scale have been successfully evaluated in several human cancers. To determine frequently novel deletion regions in oral squamous cell carcinomas (OSCCs) in Taiwan and regions specifically associated with clinicopathologic parameters and prognoses, the 400 polymorphic microsatellite markers from Applied Biosystems PRISM Linkage Mapping Set-MD10 (PE Biosystems, Foster City, CA) were used to examine 63 male primary tumors. To make sure that tumor tissue samples for genome-wide LOH screening consisted &amp;gt;90% tumor cells, LCM was performed on immunostaining slide using a PixCell laser capture microscope (Arcturus Engineering, Mountain View, CA). For increasing reliability of statistical analysis, only when a microsatellite marker was able to provide LOH information in more than 30% (&amp;gt; 19 cases) of the DNA samples was considered to be a successful allelotyping. Based on this criterion, 276 markers were included for the present study. The mean heterozygosity rate in these 276 microsatellite markers was 70.04%. The percentage of LOH among the markers was ranged from 3.85% (marker D20S171) to 65.52% (marker D18S478) with a mean of 33.63% (SD, 12.28%). Twenty-four markers displayed &amp;gt;50% LOH and chromosome regions at 2p21, 2p11.2, 5p15.1, 5q35.1 and 7q21.13 were novel frequent LOH regions not reported previously in OSCC. In this study, we found that markers with a LOH frequency &amp;gt;35% are likely to show LOHs associated with cancer-specific phenotypes. Therefore, only markers with a LOH frequency &amp;gt;35% (121 markers) were used to examine whether there were associations between LOH and the clinicopathologic parameters, including age, anatomic site, tumor stage and risk factors of oral cancer (cigarette smoking, alcohol drinking and AQ chewing) and construct minimal deleted region (MDR). Thirty-two MDRs were defined and 10 novel MDRs were noted. A loss of MDR c19r2 (19q13.42-19q13.43) was correlated significantly with cigarette smoking and a loss of MDR c14r1 (14q24.2-14q32.12) and c11r1 (11q13.4-11q25) was associated with disease-free survival. A loss of MDR c14r1 and c11r1 was associated with the magnitude of genomic instability estimated by the proportion of loci showing LOH (PLOH) and the degree of chromosomal derangement estimated by the mean fractional allelic loss (FAL) in a tumor. In conclusion, our comprehensive allelotype analyses have unveiled a few MDRs involved in the development of OSCC in Taiwan. These results provide useful clues for identification of putative tumor suppressor genes by fine mapping of the suspected MDRs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 802.

The Rutilus alburnoides complex (Cyprinidae): evidence for a hybrid origin

A genetic survey of 18 presumptive enzyme loci was conducted on members of the diploid-triploid R. alburnoides complex in order to test the hypothesis of hybrid origin. Most specimens examined were heterozygous at a high proportion of loci, with seven loci showing virtually fixed heterozygosity in some or all populations. This observation strongly supports the hypothesized hybrid ancestry. Involvement in the origin of the R. alburnoides complex was examined by comparison of allels with those observed in the other diploid cyprinids that inhabit the same Portuguese drainages. Allelic composition at the homozygous loci IDDH* and LDH-B* seems to rule out the genus Chondrostoma and other members of the genus Rutilus as one of the ancestors, and supports Leuciscus sp. as one parental species involved in the putative hybrid origin of the R. alburnoides complex. Moreover, with few exceptions, all specimens exhibited at every locus one or two alleles also present in extant populations of Leuciscus. The indentity of the other parental taxon remains unclear. Five diploid males exhibited multilocus genotypes that fit to the hypothetical genotype(s) of the ‘missing’ ancestor. However, the possibility exists that a hybrid female could produce or re-create a genotype of a parental species.

Genetic diversity in native and commercial breeds of pigs in Portugal assessed by microsatellites1

Population structure and genetic diversity in the Portuguese native breeds of pigs Alentejano (AL), Bísaro (BI), and Malhado de Alcobaça (MA) and the exotic breeds Duroc (DU), Landrace (LR), Large White (LW), and Pietrain were analyzed by typing 22 microsatellite markers in 249 individuals. In general, the markers used were greatly polymorphic, with mean total and effective number of alleles per locus of 10.68 and 4.33, respectively, and an expected heterozygosity of 0.667 across loci. The effective number of alleles per locus and expected heterozygosity were greatest in BI, LR, and AL, and least in DU. Private alleles were found in 9 of the 22 markers analyzed, mostly in AL, but also in the other breeds, with the exception of LW. The proportion of loci not in Hardy-Weinberg equilibrium in each breed analyzed ranged between 0.23 (AL) and 0.41 (BI, LW, and Pietrain), mostly because of a less than expected number of heterozygotes in those loci. With the exception of MA, all breeds showed a significant deficit in heterozygosity (F(IS); P < 0.05), which was more pronounced in BI (F(IS) = 0.175) and AL (F(IS) = 0.139), suggesting that inbreeding is a major concern, especially in these breeds that have gone through a genetic bottleneck in the recent past. The analysis of relationships among breeds, assessed by different methods, indicates that DU and AL are the more distanced breeds relative to the others, with the closest relationship being observed between LR and MA. The degree of differentiation between subpopulations (F(ST)) indicates that 0.184 of the total genetic variability can be attributed to differences among breeds. The analysis of individual distances based on allele sharing indicates that animals of the same breed generally cluster together, but subdivision is observed in the BI and LR breeds. Furthermore, the analysis of population structure indicates there is very little admixture among breeds, with each one being identified with a single ancestral population. The results of this study confirm that native breeds of pigs represent a very interesting reservoir of allelic diversity, even though the current levels of inbreeding raise concerns. Therefore, appropriate conservation efforts should be undertaken, such as adopting strategies aimed at minimizing inbreeding, to avoid further losses of genetic diversity.

Assessing genetic diversity and differentiation in Portuguese coarse-wool sheep breeds with microsatellite markers

Population structure and genetic diversity in the Portuguese native breeds of sheep Algarvia (AL), Badana (BA), Galega Bragançana (GB), Galega Mirandesa (GM), Mondegueira (MO) and Churra da Terra Quente (TQ), as well as the exotic Assaf (AS), were analyzed by typing 25 microsatellite markers in 210 individuals. The markers used exhibited high levels of polymorphism, with means for total and effective number of alleles per locus of 13.0 and 4.2, respectively, and an expected heterozygosity of 0.72 across loci. The mean number of alleles per locus and expected heterozygosity were highest in GM and GB, and lowest in AS. Exclusive alleles were found in 10 of the 25 markers analysed, mostly in the AS breed. The proportion of loci which were not in Hardy–Weinberg equilibrium in each breed ranged between 0.12 (GB) and 0.40 (AL and GM), mostly due to a lower than expected number of heterozygotes in those loci. All breeds showed a significant deficit in heterozygosity, which was more pronounced in GM ( F IS = 0.113) and BA ( F IS = 0.103), suggesting that inbreeding might be a major concern in these breeds. The analysis of relationships among breeds, assessed by different methods, indicates that AS and AL are the more distanced breeds relative to the others, while the closest relationships were observed between TQ with MO and GM with GB. The estimated F ST indicates that only 0.049 of the total genetic variability can be attributed to differences among breeds, and this ratio dropped to 0.029 when only the native breeds were considered. The analysis of individual distances based on allele-sharing indicates that only AS and AL had a tendency for animals of the same breed to cluster together, while for the other breeds there was overlapping among breeds. The results of this study confirm that native breeds of sheep represent an important reservoir of genetic diversity, even though the level of differentiation among closely located breeds tends to be rather small. For several of the breeds analyzed, the levels of inbreeding currently observed cause some apprehension, and recommend the establishment of appropriate conservation strategies, aimed at minimizing inbreeding to avoid further losses of genetic diversity.

Genetic Polymorphism in Heterogeneous Environments: The Age of Genomics

The selective mechanisms for maintaining polymorphism in natural populations has been the subject of theory, experiments, and review over the past half century. Advances in molecular genetic techniques have provided new insight into many examples of balancing selection. In addition, new theoretical developments demonstrate how diversifying selection over environments may maintain polymorphism. Tests for balancing selection in the current generation, the recent past, and the distant past provide a comprehensive approach for evaluating selective impacts. In particular, sequenced-based tests provide new ways to evaluate the long-term impact of selection on particular genes and the overall genome in natural populations. Overall, there appear to be many loci exhibiting the signal of adaptive directional selection from genomic scans, but the present evidence suggests that the proportion of loci where polymorphism is maintained by environmental heterogeneity is low. However, as more molecular genetic details become available, more examples of polymorphism maintained by selection in heterogeneous environments may be found.

Allozyme variation of Cyclobalanopsis championii (Fagaceae), a narrowly distributed species in southern Taiwan.

Allozyme genetic variability in five natural populations of Cyclobalanopsis championii (Fagaceae) in Taiwan was investigated using 12 loci from 9 enzyme systems. The average values of parameters describing within-population variation, expected heterozygosity (He = 0.151), the percentage of polymorphic loci per individual (P = 50%), the average number of alleles per locus (A = 1.7), effective number of alleles per locus (Ae = 1.25), and the average number of alleles per polymorphic loci (AP = 2.2) are comparable to those of other long-lived woody plants. The overall fixation index (Fis = 0.208) indicates a significant deficiency of heterozygotes at the population level. Allelic frequency deviation from Hardy-Weinberg equilibrium was found for different loci in different populations. An exact test for population differentiation using the Tools for Population Genetic Analyses program also indicates that allelic frequencies among populations are significantly different (P < .001). Among-population variation, Gst, accounted for 9.2% of the total heterozygosity. The population at Shouchia and the southernmost population Nanjenshan had higher inbreeding coefficients (0.177 and 0.153, respectively) than did the northern populations. Genetic drift is supported by the observations of the variance components of linkage disequilibrium and a large proportion of loci in Nanjenshan and Shouchia that show pairwise locus disequilibrium. We believe continuous genetic drift in the southern populations will increase genetic divergence among populations of C. championii in Taiwan. Significant correlation was found between elevation and expected heterozygosity. We therefore inferred that temperature is the most important ecological factor to influence the genetic diversity of C. championii.

Genomic alterations (LOH, MI) on chromosome 17q21-23 and prognosis of sporadic colorectal cancer.

Genomic alterations at the long arm of chromosome 17, and in particular at the nm23 locus, are still controversial in colorectal cancer (CRC). Our aim was to investigate the possible relationship of loss of heterozygosity (LOH) and microsatellite instability (MI), at 4 microsatellite loci spanning the 17q21-23 region, to the risk of liver metastasis and nm23 protein expression. Genomic DNA extracted from 58 primary and 54 liver secondary formalin-fixed and paraffin-embedded CRCs was obtained from 82 patients. A fluorescent PCR coupled with an automated DNA sequencer was applied. Increasing fraction of loci showing LOH was positively associated with risk of liver metastases (logrank test for trend, p = 0.005); this remained independent after adjusting to T-stage (Cox regression, p = 0.022), N-stage (p = 0.007), or Dukes' stage (p = 0.012). Conversely, increasing frequency of MI was associated with a reduced risk of liver metastases in Dukes' B tumours (logrank test for trend, p = 0.032). When comparing 30 primary and matched liver secondary lesions, we found concordant genomic alteration in 72% (NME1) to 43% (D17S579). Finally, we observed a trend in association between the proportion of loci with LOH and nm23 positivity (chi2 test for trend, p = 0.024). Our findings suggest that genomic alterations in the 17q21-23 region may affect prognosis of CRC as well as regulation of the nm23 protein expression via an unknown underlying mechanism.

Description and power analysis of two tests for detecting recent population bottlenecks from allele frequency data.

When a population experiences a reduction of its effective size, it generally develops a heterozygosity excess at selectively neutral loci, i.e., the heterozygosity computed from a sample of genes is larger than the heterozygosity expected from the number of alleles found in the sample if the population were at mutation drift equilibrium. The heterozygosity excess persists only a certain number of generations until a new equilibrium is established. Two statistical tests for detecting a heterozygosity excess are described. They require measurements of the number of alleles and heterozygosity at each of several loci from a population sample. The first test determines if the proportion of loci with heterozygosity excess is significantly larger than expected at equilibrium. The second test establishes if the average of standardized differences between observed and expected heterozygosities is significantly different from zero. Type I and II errors have been evaluated by computer simulations, varying sample size, number of loci, bottleneck size, time elapsed since the beginning of the bottleneck and level of variability of loci. These analyses show that the most useful markers for bottleneck detection are those evolving under the infinite allele model (IAM) and they provide guidelines for selecting sample sizes of individuals and loci. The usefulness of these tests for conservation biology is discussed.

Breeding strategies and genetic variation in European roe deer Capreolus capreolus populations

Kurt P., Hartl G. B. and Volk F. 1993. Breeding strategies and genetic variation in European roe deer Capreolus capreolus populations. [In: Ecological genetics in mam­ mals. G. B. Hartl and J. Markowski, eds], Acta theriol. 38, Suppl. 2: 187 - 194. Based on previously published electrophoretic data on genetic variability in 31 roe deer Capreolus capreolus Linnaeus, 1758 populations, the proportion of loci poly­ morphic (P), average heterozygosity (H), and the inbreeding coefficient (Fis) were examined for relationships with the social structure displayed in the various-popu­ lations. Our hypothesis was that genetic variability is lower and F/s-values are more positive in populations where males maintain a stable pattern of territories during the rutting season (forest dwelling roe deer) than in those characterized by pronounced fluctuations in population structure, both within and among seasons (field or mountain dwelling roe deer). P and H did not show differences among those two groups. Fis was significantly more positive in the ‘forest’ roe deer than in the more migratory ‘type’, but only when populations subjected to high culling rates were excluded from the analysis. Highly negative Fis-values in forest populations with high culling rates suggested that considerable perturbations of population structure may be caused by hunting. In conclusion, the ‘forest’ roe deer and the ‘field’ roe deer do not represent two distinct ecotypes with a particular genetic integrity, but rather reflect the consid­ erable behavioural plasticity of the species. Forschungsinstitut fur Wildtierkunde und Okologie der Veterinarmedizinischen Uni­ versitat Wien, Savoyenstrase 1, A-1160 Vienna, Austria (FK, GBH, FV)

Multilocus enzyme electrophoresis of major O-antigen reference strains of Pseudomonas aeruginosa.

Multilocus enzyme electrophoresis was used to characterize 27 Pseudomonas aeruginosa serogroup reference strains used in the major O-antigen schemes according to which Pseudomonas aeruginosa has been typed. Sixteen enzyme loci were assayed, ten of which showed electrophoretic variation. Genetic diversity was expressed for each enzyme locus, and as the mean allelic diversity of loci. Ten electrophoretic types were identified among the strains. The genetic distance between pairs of electrophoretic types was expressed as the proportion of loci at which similar alleles occurred. More than 80% similarity was observed between any pair of electrophoretic types, reflecting the homogeneity of multilocus genotypes within this species. Similarity between electrophoretic types was represented in the form of a dendrogram and by multi-dimensional scaling. Three distinct clusters of electrophoretic types were revealed; within each the serogroups appeared to be randomly distributed.

Genetic Variation within and among Populations of Ferns

The evolutionary potential of a species depends in part on the levels of genetic variation maintained within the species and also on the distribution of that variation both within and among its populations. Analyses of electrophoretic data for seed plants have resulted in several generalizations regarding levels and distribution of genetic variation: (1) High levels of genetic variation are maintained in populations of species with outcrossing mating systems, wide (regional) geographic distributions, habitats of late successional stages, and wind-pollination (Hamrick et al., 1979), (2) Inbreeding populations often exhibit genetic structure (i.e. a nonrandom distribution of genotypes in space), whereas genotypes are typically randomly distributed in highly outcrossing populations (Loveless & Hamrick, 1984), and (3) Outcrossing species maintain genetic variation within single populations, whereas inbreeding species distribute relatively more of their genetic variation among rather than within populations (Brown, 1979). Because ferns differ from seed plants in several life-history characteristics, especially in their life cycle and potential for large amounts of interpopulational gene flow via spore dispersal, it is unclear whether species of ferns follow these generalizations. Therefore, we address the following topics in homosporous ferns: (1) levels of genetic variation within populations of ferns, (2) the genetic structure of populations of ferns, and (3) the genetic structure of species of ferns. For all three topics we review the patterns of genetic variation that have been observed in ferns and then discuss factors that may contribute to these patterns. Electrophoretic data from the literature will be used to provide estimates of genetic variation. Data from the literature will be supplemented by our published and previously unpublished data for North American species of Polystichum. LEVELS OF GENETIC VARIATION WITHIN POPULATIONS OF FERNS Typical measures used to quantify the amount of genetic variation present in natural populations are P, the proportion of loci that are polymorphic in the population, A, the mean number of alleles per locus in a population, H, mean heterozygosity in a population (that is, heterozygosity expected at HardyWeinberg equilibrium), and Hobs, observed heterozygosity in the population. Measures of genetic variation for most of the diploid fern species that have been analyzed are presented in Table 1. Mean values for each measure of genetic variation cover a broad range. P ranges from 0.067 in Polystichum lonchitis to 0.635 in Pellaea andromedifolia. A ranges from 1.08 in P. lonchitis to 2.62 in Bommeria hispida. Hobs ranges from 1.08 in P. lonchitis to 0.221 in P. andromedifolia.