共查询到20条相似文献,搜索用时 15 毫秒
1.
Usually, genetic correlations are estimated from breeding designs in the laboratory or greenhouse. However, estimates of the genetic correlation for natural populations are lacking, mostly because pedigrees of wild individuals are rarely known. Recently Lynch (1999) proposed a formula to estimate the genetic correlation in the absence of data on pedigree. This method has been shown to be particularly accurate provided a large sample size and a minimum (20%) proportion of relatives. Lynch (1999) proposed the use of the bootstrap to estimate standard errors associated with genetic correlations, but did not test the reliability of such a method. We tested the bootstrap and showed the jackknife can provide valid estimates of the genetic correlation calculated with the Lynch formula. The occurrence of undefined estimates, combined with the high number of replicates involved in the bootstrap, means there is a high probability of obtaining a biased upward, incomplete bootstrap, even when there is a high fraction of related pairs in a sample. It is easier to obtain complete jackknife estimates for which all the pseudovalues have been defined. We therefore recommend the use of the jackknife to estimate the genetic correlation with the Lynch formula. Provided data can be collected for more than two individuals at each location, we propose a group sampling method that produces low standard errors associated with the jackknife, even when there is a low fraction of relatives in a sample. 相似文献
2.
Kruuk LE 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2004,359(1446):873-890
Estimating the genetic basis of quantitative traits can be tricky for wild populations in natural environments, as environmental variation frequently obscures the underlying evolutionary patterns. I review the recent application of restricted maximum-likelihood "animal models" to multigenerational data from natural populations, and show how the estimation of variance components and prediction of breeding values using these methods offer a powerful means of tackling the potentially confounding effects of environmental variation, as well as generating a wealth of new areas of investigation. 相似文献
3.
Estimating levels of gene flow in natural populations 总被引:4,自引:2,他引:2
Slatkin M 《Genetics》1981,99(2):323-335
The results from a simulation model of selection, mutation and genetic drift in a geographically subdivided population are presented. The infinite-alleles mutation model of Kimura and Crow (1964) is asumed, and both advantageous and deleterious mutations are considered. It is shown that the average frequency of an allele conditioned on the number of local populations it appears in-the conditional average frequency-is approximately independent of both the selection intensity and mutation rates assumed, but depends strongly on the overall level of gene flow. This result justifies the use of the conditional average frequency to obtain a rough estimate of the level of gene flow in a subdivided population. Data from 16 species are presented and discussed. There are large differences in the conditional average frequencies of different species, although there is some consistency within taxa. Some species apparently have high levels of gene flow and others, particularly salamanders, have low levels. Alternative explanations for the patterns found in the data are considered. 相似文献
4.
5.
Quantitative genetic studies in natural populations have been rare because they require large breeding programmes or known pedigrees. The relatedness that has been estimated from molecular markers can now be used to substitute for breeding, allowing studies of previously inaccessible species. Many behavioural ecologists have a sufficient number of markers and study species with characteristics that are amenable to this approach. It is now time to combine studies of selection with studies of genetic variation for a more complete understanding of behavioural evolution. 相似文献
6.
The selection coefficient, s, quantifies the strength of selection acting on a genetic variant. Despite this parameter's central importance to population genetic models, until recently we have known relatively little about the value of s in natural populations. With the development of molecular genetic techniques in the late 20th century and the sequencing technologies that followed, biologists are now able to identify genetic variants and directly relate them to organismal fitness. We reviewed the literature for published estimates of natural selection acting at the genetic level and found over 3000 estimates of selection coefficients from 79 studies. Selection coefficients were roughly exponentially distributed, suggesting that the impact of selection at the genetic level is generally weak but can occasionally be quite strong. We used both nonparametric statistics and formal random‐effects meta‐analysis to determine how selection varies across biological and methodological categories. Selection was stronger when measured over shorter timescales, with the mean magnitude of s greatest for studies that measured selection within a single generation. Our analyses found conflicting trends when considering how selection varies with the genetic scale (e.g., SNPs or haplotypes) at which it is measured, suggesting a need for further research. Besides these quantitative conclusions, we highlight key issues in the calculation, interpretation, and reporting of selection coefficients and provide recommendations for future research. 相似文献
7.
The estimation of relatedness within social groups, such as the colonies of a population of social insects, is an important field for evaluating hypotheses concerning the evolution and maintenance of social behaviour. The methodology of this estimation from genetic data in the absence of pedigree information has been poorly understood; we develop this methodology for b, the regression coefficient of relatedness, and discuss its applications. Both b and G (the pedigree coefficient of relatedness) are potentially asymmetric coefficients, whereas φ, r, and FST are necessarily symmetric. We develop an estimator for b suitable for small samples, and also one for standard deviation, and examine the properties of both using sampling simulations. The b estimator returns values slightly below E(b), and the standard deviation estimator yields conservative confidence intervals. A comparative study of b and FST shows that, given the same set of data, b is estimated with greater reliability than is FST. As is the case for FST, b can be used to examine population structure at various levels, and b possesses the advantage of an estimator for its standard error, which can also be used to test for heterogeneity among the loci surveyed. The actual numbers of identical genes held in common by interacting individuals, and not simply their proportions, need to be considered in using coefficients of relatedness in inclusive fitness calculations. This necessity is handled by the weighted coefficients of relatedness, G′ and b′, which have been referred to in the literature as r (as have most relatedness measures). 相似文献
8.
Quantitative genetic parameters are nowadays more frequently estimated with restricted maximum likelihood using the 'animal model' than with traditional methods such as parent-offspring regressions. These methods have however rarely been evaluated using equivalent data sets. We compare heritabilities and genetic correlations from animal model and parent-offspring analyses, respectively, using data on eight morphological traits in the great reed warbler (Acrocephalus arundinaceus). Animal models were run using either mean trait values or individual repeated measurements to be able to separate between effects of including more extended pedigree information and effects of replicated sampling from the same individuals. We show that the inclusion of more pedigree information by the use of mean traits animal models had limited effect on the standard error and magnitude of heritabilities. In contrast, the use of repeated measures animal model generally had a positive effect on the sampling accuracy and resulted in lower heritabilities; the latter due to lower additive variance and higher phenotypic variance. For most trait combinations, both animal model methods gave genetic correlations that were lower than the parent-offspring estimates, whereas the standard errors were lower only for the mean traits animal model. We conclude that differences in heritabilities between the animal model and parent-offspring regressions were mostly due to the inclusion of individual replicates to the animal model rather than the inclusion of more extended pedigree information. Genetic correlations were, on the other hand, primarily affected by the inclusion of more pedigree information. This study is to our knowledge the most comprehensive empirical evaluation of the performance of the animal model in relation to parent-offspring regressions in a wild population. Our conclusions should be valuable for reconciliation of data obtained in earlier studies as well as for future meta-analyses utilizing estimates from both traditional methods and the animal model. 相似文献
9.
Zintzaras E 《Journal of genetics》2011,90(1):51-58
Knowledge of genetic correlations is essential to understand the joint evolution of traits through correlated responses to
selection, a difficult and seldom, very precise task even with easy-to-breed species. Here, a simulation-based method to estimate
genetic correlations and genetic covariances that relies only on phenotypic measurements is proposed. The method does not
require any degree of relatedness in the sampled individuals. Extensive numerical results suggest that the propose method
may provide relatively efficient estimates regardless of sample sizes and contributions from common environmental effects. 相似文献
10.
L��zaro Jos�� Chaves Roland Vencovsky Rossana Serrato Mendon?a Silva Mariana Pires de Campos Telles Maria Imaculada Zucchi Alexandre Siqueira Guedes Coelho 《Conservation Genetics》2011,12(2):569-576
Inbreeding and inbreeding depression are important issues in the biology and conservation of natural plant and animal populations, primarily when subpopulation sizes are reduced due to habitat fragmentation. In this study, we propose a method for estimating inbreeding depression in progenies of natural plant populations, combining the estimation of the fixation index by codominant markers with the experimental evaluation of quantitative traits. Our technique estimates apparent inbreeding depression in structured natural populations using the linear regression of phenotypic means on the inbreeding coefficients estimated with codominant markers. This method was applied to data from 112 maternal progenies of 10 natural subpopulations of Eugenia dysenterica DC, a fruiting tree species from the Brazilian savanna (Cerrado). The results show that the proposed method was efficient at detecting the presence of inbreeding depression for seedling emergence and initial growth traits in the species. This corroborates the importance of maintaining high levels of heterozygosity for in situ conservation or genetic restoration of natural populations. 相似文献
11.
12.
Mitchell-Olds T 《Trends in ecology & evolution》1995,10(8):324-328
DNA markers allow us to study quantitative trait loci (QTL) - the genes that control adaptation and quantitative variation. Experiments can map the genes responsible for quantitative variation and address the evolutionary and ecological significance of this variation. Recent studies suggest that major genes segregate within and among natural populations. It is now feasible to study the genes that cause morphological variation, life history trade-offs, heterosis and speciation. These methods can determine the role of epistasis and genotype-by-environment interaction in maintaining genetic variation. QTL mapping is an important tool used to address evolutionary and ecological questions of long-standing interest. 相似文献
13.
Gina L. Conte Matthew E. Arnegard Catherine L. Peichel Dolph Schluter 《Proceedings. Biological sciences / The Royal Society》2012,279(1749):5039-5047
Genomic and genetic methods allow investigation of how frequently the same genes are used by different populations during adaptive evolution, yielding insights into the predictability of evolution at the genetic level. We estimated the probability of gene reuse in parallel and convergent phenotypic evolution in nature using data from published studies. The estimates are surprisingly high, with mean probabilities of 0.32 for genetic mapping studies and 0.55 for candidate gene studies. The probability declines with increasing age of the common ancestor of compared taxa, from about 0.8 for young nodes to 0.1–0.4 for the oldest nodes in our study. Probability of gene reuse is higher when populations begin from the same ancestor (genetic parallelism) than when they begin from divergent ancestors (genetic convergence). Our estimates are broadly consistent with genomic estimates of gene reuse during repeated adaptation to similar environments, but most genomic studies lack data on phenotypic traits affected. Frequent reuse of the same genes during repeated phenotypic evolution suggests that strong biases and constraints affect adaptive evolution, resulting in changes at a relatively small subset of available genes. Declines in the probability of gene reuse with increasing age suggest that these biases diverge with time. 相似文献
14.
W Amos J Harwood 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1998,353(1366):177-186
Genetic variability is the clay of evolution, providing the base material on which adaptation and speciation depend. It is often assumed that most interspecific differences in variability are due primarily to population size effects, with bottlenecked populations carrying less variability than those of stable size. However, we show that population bottlenecks are unlikely to be the only factor, even in classic case studies such as the northern elephant seal and the cheetah, where genetic polymorphism is virtually absent. Instead, we suggest that the low levels of variability observed in endangered populations are more likely to result from a combination of publication biases, which tend to inflate the level of variability which is considered ''normal'', and inbreeding effects, which may hasten loss of variability due to drift. To account for species with large population sizes but low variability we advance three hypotheses. First, it is known that certain metapopulation structures can result in effective population sizes far below the census size. Second, there is increasing evidence that heterozygous sites mutate more frequently than equivalent homozygous sites, plausibly because mismatch repair between homologous chromosomes during meiosis provides extra opportunities to mutate. Such a mechanism would undermine the simple relationship between heterozygosity and effective population size. Third, the fact that related species that differ greatly in variability implies that large amounts of variability can be gained or lost rapidly. We argue that such cases are best explained by rapid loss through a genome-wide selective sweep, and suggest a mechanism by which this could come about, based on forced changes to a control gene inducing coevolution in the genes it controls. Our model, based on meiotic drive in mammals, but easily extended to other systems, would tend to facilitate population isolation by generating molecular incompatabilities. Circumstances can even be envisioned in which the process could provide intrinsic impetus to speciation. 相似文献
15.
Captive breeding and the genetic fitness of natural populations 总被引:2,自引:0,他引:2
Many populations of endangered species are subject to recurrent introductions of individuals from an alternative setting where selection is either relaxed or in a direction opposite to that in the natural habitat. Such population structures, which are common to captive breeding and hatchery programs, can lead to a scenario in which alleles that are deleterious (and ordinarily keptat low levels) in the wild can rise to high frequencies and, in some cases, go to fixation. We outline how these genetic responses to supplementation candevelop to a large enough extent to impose a substantial risk of extinction for natural populations on time scales of relevance to conservation biology.The genetic supplementation load can be especially severe when a captive population that is largely closed to import makes a large contribution to the breeding pool of individuals in the wild, as these conditions insure thatthe productivity of the two-population system is dominated by captive breeders. However, a substantial supplementation load can even develop when the captive breeders are always derived from the wild, and in general, a severe restriction of gene flow into the natural population is required to reduce this load to an insignificant level. Domestication selection (adaptation to the captive environment) poses a particularly serious problem because it promotes fixations of alleles that are deleterious in nature, thereby resulting in a permanent load that cannot be purged once the supplementation program is truncated. Thus, our results suggest that the apparent short-term demographic advantages of a supplementation program can be quite deceiving. Unless the selective pressures of the captive environmentare closely managed to resemble those in the wild, long-term supplementation programs are expected to result in genetic transformations that can eventually lead to natural populations that are no longer capable of sustaining themselves. 相似文献
16.
M. E. Sartor R. N. Rebozzio C. L. Quarin F. Espinoza 《Plant Systematics and Evolution》2013,299(7):1295-1306
Paspalum has many multiploid species displaying a wide range of ploidy levels and reproductive systems including apomixis. However, not much is known about the genetic structure of natural populations of the apomictic species of Paspalum. The aim of this work was to evaluate the genetic diversity of several natural populations belonging to five species of Paspalum. A total of 13 populations were analyzed using amplified fragment length polymorphism (AFLP). The AFLP data revealed maximal genotypic diversity and significant levels of genetic diversity in diploid and mixed diploid–tetraploid populations of P. denticulatum and P. rufum, where all individuals represent different genotypes. This may be mainly due to the reproductive system of diploid members and the gene flow from diploids to polyploids. The pure populations of tetraploids consist of either multiple genotypes (P. nicorae) or of one dominant genotype with a few deviated genotypes (P. denticulatum and P. lividum). Here, the main source of variability may be the residual sexuality, which continues generating new genotypic combinations. The hexaploid populations of P. buckleyanum consist of a single AFLP genotype and each population represents a particular genotype suggesting that populations arose from independent polyploidization events. This study represents one of the first reports of genetic diversity in natural populations of several Paspalum agamic complexes. Apomixis in these five species may be acting as a successful method for the dispersion of better adapted genotypes. 相似文献
17.
Carolina L. Pometti Cecilia F. Bessega Juan C. Vilardi Beatriz O. Saidman 《Tree Genetics & Genomes》2012,8(4):911-924
Acacia caven is a South American species which shows remarkable climate tolerance and ecological adaptability; as such, this species is suitable for colonizing anthropogenically degraded sites. This species is widely distributed, and six varieties have been described based on both morphological traits and molecular markers. Moreover, Aronson (1992) suggests that, for this species, geographical separation could be associated with ecological differentiation. In this study, amplified fragment length polymorphisms were used to study genetic variation within and among 15 populations of A. caven from five eco-regions of Argentina and to investigate (1) whether the varieties are genetically coherent, (2) whether the varieties correspond consistently to a single eco-region, (3) the proportion of the species diversity explained within and among varieties and eco-regions. Eight of the 225 bands appear to be under positive selection. The remaining 217 neutral loci showed a high percentage of polymorphism (99.1%). The estimates of genetic diversity H j were generally high. The F ST (0.315) was highly significant, providing evidence for genetic structure among populations. Hierarchical analysis of molecular variance indicated that variation among eco-regions was 8.2% and highly significant. The higher component of variance was found within populations (67.5%). STRUCTURE analysis suggested that the optimal number of K?=?11. The results showed that, in most cases, geographic separation is associated with ecological differentiation. Since differentiation of A. caven populations studied here in eco-regions was highly significant, sampling should include a large number of trees within populations as well as covering the wide ecological diversity of the species. 相似文献
18.
锥栗自然居群遗传多样性的ISSR分析 总被引:1,自引:0,他引:1
采用20条ISSR分子标记对栗属中国特有种-锥栗(Castanea henryi)的16个自然居群进行了遗传多样性与遗传关系分析。在449份试材上共扩增得到379个位点,其中多态性位点378个,多态性位点百分率(PPL)达99.74%,平均期望杂合度(He)为0.2950,Shannon信息指数(I)为0.4522;居群水平遗传多样性为46.09%,且不同居群遗传多样性水平有较大差异,16个自然居群中以湘西居群的遗传多样性水平最高(PPL=53.30%,He=0.1861,I=0.2781),其次为靖州、庆元、昭通及都江堰居群,南平居群最低(PPL=36.94%,He=0.1202,I=0.1817)。Nei’s遗传多样性和AMOVA分析表明,居群间产生了较大的遗传分化(Gst=0.4466),锥栗自然居群内的遗传变异稍占优势(52.51%)。UPGMA聚类分析将16个锥栗居群分为2大类5亚类。湘西地区可能是锥栗的次生分布中心和现代遗传多样性分布中心,是锥栗研究的资源中心,也是最有价值的基因库,需要重点保护。 相似文献
19.
20.
The importance of infectious disease in the survival and adaptation of animal populations is rapidly becoming apparent. Throughout evolution, animal species have been continually afflicted with devastating disease outbreaks which have influenced the demographic and genetic status of the populations. Some general population consequences of such epidemics include selection for disease resistance, the occasional alteration of host gene frequencies by a genetic 'founder effect' after an outbreak, and genetic adaptation of parasites to abrogate host defense mechanisms. A wide variety of host cellular genes which are polymorphic within species and which confer a regulatory effect on the outcome of infectious diseases has recently been discovered. The critical importance of maintaining genetic diversity with respect to disease defense genes in natural populations is indicated by certain populations which have reduced genetic variability and apparent increased vulnerability to infectious disease. 相似文献