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1.
Ziziphus jujuba ‘Jinsixiaozao’ is one of the most elite Chinese jujube variety with a long cultivation history. There are many different types and newly developed accessions of ‘Jinsixiaozao’ reported, however the names are in chaotic. For the accurate identification of the accessions and estimating the genetic diversity, the diversity and relationships of the 45 ‘Jinsixiaozao’ accessions were evaluated by 49 morphological traits and 24 highly polymorphic genomic SSR primers. The UPGMA dendrogram based on morphological traits separated the accessions into four major groups with Euclidean distance ranging from 4.26 to 12.26. Six of 24 SSR primers produced polymorphic patterns with a total of 17 alleles. Cluster analysis using UPGMA and Jaccard‘s coefficient grouped the accessions into eight groups. The SSR markers failed to distinguish the majority of the analyzed accessions, and a negative percentage of variation was partitioned. These results indicated low genetic diversity among the collected accessions. The mantel test revealed a weak negative correlation (r = −0.051) between the morphological dissimilarity matrix and that based on SSR markers.  相似文献   

2.
Physical disturbance has often been invoked to control genotypic diversity in sessile clonal organisms, yet experimental evidence is lacking. I studied the effects of physical disturbance on genet dynamics and genotypic diversity in a clonal marine angiosperm, Zostera marina (eelgrass). In replicated plots of 1 m2, the vegetation canopy was removed in gaps of zero (control), 25%, 50% and 75% of the area (n = 6 replicates). Before removal and during two consecutive years, the genotypic composition was determined using genetic markers (DNA microsatellites) in a 5 x 5 pixel grid per plot. An aggregate index of genet dynamics summarizing recruitment, increase, loss and decrease of clones was maximal at intermediate disturbance levels (quadratic polynomial P = 0.02). Physical disturbance also increased the occurrence of new genotypes, possibly reflecting recruitment (linear model, P < 0.05). Contrary to expectations, there was no competitive advantage of more heterozygous genotypes over less heterozygous ones. In the absence of disturbance, in particular, clones with lower individual heterozygosity were more likely to increase in area over a 1-year time period than more heterozygous ones, while there was no such correlation in plots with disturbance (logistic model, P(disturbance x heterozygosity) = 0.036). Undisturbed plots revealed background recruitment independent of canopy gaps, suggesting that Z. marina exhibits a strategy of continual recruitment. Effects of experimental disturbance (linear or quadratic) on clonal diversity were not detectable. Instead, initial (pretreatment) clonal diversity accounted for between 68% and 91% of the variance in diversity, indicating remarkable resilience of genotypic diversity in the face of physical disturbance.  相似文献   

3.
The two most important components of biodiversity, species diversity and genetic diversity, have generally been treated as separate topics, although a coordination between both components is believed to be critical for ecosystem stability and resilience. Based on a new trait concept that allows for the assessment of genetic diversity across species, the relationship between species diversity and genetic diversity was examined in eight forest tree communities composed of different tree genera including both climax and pioneer species. It was intended to check whether a trade-off exists between the two diversity components as was found in a few studies on animal species.Using several isozyme-gene systems as genetic markers, the genetic diversity across species within each of the tree communities was determined by two measures, the commonly used intraspecific genetic diversity averaged over species and the recently developed transspecific genetic diversity per species. Both data sets were compared with the corresponding community-specific species diversity resulting in a positive relationship between the two diversity components. A statistically significant positive correlation was established between the transspecific genetic diversity per species and the species diversity for three isozyme-gene systems. Beyond that, consistent results were obtained using different parameters of the diversity measure which characterize the total, the effective and the number of prevalent variants. The number of prevalent variants reflected most significantly the non-randomness of the observed diversity patterns.These findings can be explained by the observation that the pioneer tree species reveal a by far higher genetic diversity than the climax tree species, which means that an increase in species diversity, due to the addition of several pioneer species at the expense of one or two climax species, goes along with an increase in the level of genetic diversity. Forest tree communities with the highest degree of species diversity exhibit therefore the highest transspecific genetic diversity per species. This result was discussed with regard to the particular composition and stability of forest tree communities.  相似文献   

4.
Knowledge about genetic variability of a crop allows for more efficient and effective use of resources in plant improvement programs. The genetic variation within temperate maize has been studied extensively, but the levels and patterns of diversity in tropical maize are still not well understood. Brazilian maize germplasm represents a very important pool of genetic diversity due to many past introductions of exotic material. To improve our knowledge of the genetic diversity in tropical maize inbred lines, we fingerprinted 85 lines with 569 AFLP bands and 50 microsatellite loci. These markers revealed substantial variability among lines, with high rates of polymorphism. Cluster analysis was used to identify groups of related lines. Well-defined groups were not observed, indicating that the tropical maize studied is not as well organized as temperate maize. Three types of genetic distance measurements were applied (Jaccard’s coefficient, Modified Rogers’ distance and molecular coefficient of coancestry), and the values obtained with all of them indicated that the genetic similarities were small among the lines. The different coefficients did not substantially affect the results of cluster analysis, but marker types had a large effect on genetic similarity estimates. Regardless of genetic similarity coefficient used, estimates based on AFLPs were poorly correlated with those based on SSRs. Analyses using AFLP and SSR data together do not seem to be the most efficient manner of assessing variability in highly diverse materials because the result was similar to using AFLPs alone. It was seen that molecular markers can help to organize the genetic variability and expose useful diversity for breeding purposes.  相似文献   

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Microsatellite variability is widely used to infer levels of genetic diversity in natural populations. However, the ascertainment bias caused by typically selecting only the most polymorphic markers in the genome may lead to reduced sensitivity for judging genome-wide levels of genetic diversity. To test this potential limitation of microsatellite-based approaches, we assessed the degree of nucleotide diversity in noncoding regions of eight different carnivore populations, including inbred as well as outbred populations, by sequencing 10 introns (5.4–5.7 kb) in 20 individuals of each population (wolves, coyotes, wolverines and lynxes). Estimates of nucleotide diversity varied 30-fold (7.1 × 10−5 –2.1 × 10−3), with densities of one single nucleotide polymorphism every 112–5446 bp. Microsatellite genotyping (10–27 markers) of the same animals revealed mean multilocus heterozygosities of 0.54–0.78, a 1.4-fold difference among populations. There was a positive yet not perfect ( r 2  = 0.70) correlation between microsatellite marker heterozygosity and nucleotide diversity at the population level. For example, point estimates of nucleotide diversity varied in some cases with an order of magnitude despite very similar levels of microsatellite marker heterozygosity. Moreover, at the individual level, no significant correlation was found. Our results imply that variability at microsatellite marker sets typically used in population studies may not accurately reflect the underlying genomic diversity. This suggests that researchers should consider using resequencing-based approaches for assessing genetic diversity when accurate inference is critical, as in many conservation and management contexts.  相似文献   

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9.
Kincaid’s lupine (Lupinus oreganus), a threatened perennial legume of western Oregon grasslands, is composed of small, fragmented populations that have consistently low natural seed set, suggesting they may have accumulated high enough levels of genetic load to be candidates for genetic rescue. We used simple sequence repeat (SSR) loci, both nuclear DNA and chloroplast DNA, to screen populations throughout the species’ range for evidence of severe inbreeding and recent genetic bottlenecks due to habitat fragmentation. After genotyping about 40% of the known populations, only one of 24 populations had strong statistical evidence for a recent genetic bottleneck (H e > H eq). Both mean nSSR fixation coefficients and genetic diversity did not statistically differ between very small, small, medium, and large lupine population size classes. Within population chloroplast DNA haplotype number was high for an animal pollinated species, ≈4.2 haplotypes/population, and within population haplotype diversity was also relatively evenly distributed. Within population patterns of nSSR and cpSSR genetic diversity suggest that genetic diversity has not been lost over the last century of habitat fragmentation. With genet lifespan thought to exceed 100 years, overlap of several to many generations, and substantial reductions in seed set from inbreeding depression that shifts cohort composition towards those generated by outcrossing events, Kincaid’s lupine is likely maintain the currently high levels of within population genetic diversity. The case of Kincaid’s lupine provides an example of how the assumptions of severe inbreeding depression with small population size and habitat fragmentation can be inaccurate.  相似文献   

10.
Obesity is accompanied by the development of chronic low-grade inflammation in adipose tissue. The presence of chronic inflammatory response along with metabolically harmful factors released by adipose tissue into the circulation is associated with several metabolic complications of obesity such as type 2 diabetes mellitus or accelerated atherosclerosis. The present review is focused on macrophages and lymphocytes and their possible role in low-grade inflammation in fat. Both macrophages and lymphocytes respond to obesity-induced adipocyte hypertrophy by their migration into adipose tissue. After activation and differentiation, they contribute to the development of local inflammatory response and modulation of endocrine function of adipose tissue. Despite intensive research, the exact role of lymphocytes and macrophages within adipose tissue is only partially clarified and various data obtained by different approaches bring ambiguous information with respect to their polarization and cytokine production. Compared to immunocompetent cells, the role of adipocytes in the obesity-related adipose tissue inflammation is often underestimated despite their abundant production of factors with immunomodulatory actions such as cytokines or adipokines such as leptin, adiponektin, and others. In summary, conflicting evidence together with only partial correlation of in vitro findings with true in vivo situation due to great heterogeneity and molecular complexity of tissue environment calls for intensive research in this rapidly evolving and important area.  相似文献   

11.
Commercial screening services for inheritable diseases raise concerns about pressure on parents to terminate “imperfect babies”. Subject Categories: S&S: Economics & Business, Molecular Biology of Disease

Nearly two decades have passed since the first draft sequences of the human genome were published at the eyewatering cost of nearly US$3 billion for the publicly funded project. Sequencing costs have dropped drastically since, and a range of direct‐to‐consumer genetics companies now offer partial sequencing of your individual genome in the US$100 price range, and whole‐genome sequencing for less than US$1,000.While such tests are mainly for personal peruse, there have also been substantial drops in price in clinical genome sequencing, which has greatly enabled the study of and screening for inheritable disorders. This has both advanced our understanding of these diseases in general, and benefitted early diagnosis of many genetic disorders, which is crucial for early and efficient treatment. Such detection can, in fact, now occur long before birth: from cell‐free DNA testing during the first trimester of pregnancy, to genetic testing of embryos generated by in vitro fertilization, to preconception carrier screening of parents to find out if both are carriers of an autosomal recessive condition. While such prenatal testing of foetuses or embryos primarily focuses on diseases caused by chromosomal abnormalities, technological advances allow also for the testing of an increasing number of heritable monogenic conditions in cases where the disease‐causing variants are known.The medical benefits of such screening are obvious: I personally have lost two pregnancies, one to Turner''s syndrome and the other to an extremely rare and lethal autosomal recessive skeletal dysplasia, and I know first‐hand the heartbreak and devastation involved in finding out that you will lose the child you already love so much. It should be noted though that, very rarely, Turner syndrome is survivable and the long‐term outlook is typically good in those cases (GARD, 2021). In addition, I have Kallmann syndrome, a highly genetically complex dominant endocrine disorder (Maoine et al, 2018), and early detection and treatment make a difference in outcome. Being able to screen early during pregnancy or childhood therefore has significant benefits for affected children. Many other genetic disorders similarly benefit from prenatal screening and detection.But there is also obvious cause for concern: the concept of “designer babies” selected for sex, physical features, or other apparent benefits is well entrenched in our society – and indeed culture – as a product from a dystopian future. Just as a recent example, Philipp Ball, writing for the Guardian in 2017, described designer babies as “an ethical horror waiting to happen” (Ball, 2017). In addition, various commercial enterprises hope to capitalize on these screening technologies. Orchid Inc claims that their preconception screening allows you to “… safely and naturally, protect your baby from diseases that run in your family”. The fact that this is hugely problematic if not impossible from a technological perspective has already been extensively clarified by Lior Pachter, a computational biologist at Caltech (Pachter, 2021). George Church at Harvard University suggested creating a DNA‐based dating app that would effectively prevent people who are both carriers for certain genetic conditions from matching (Flynn, 2019). Richard Dawkins at Oxford University recently commented that “…the decision to deliberately give birth to a Down [syndrome] baby, when you have the choice to abort it early in the pregnancy, might actually be immoral from the point of view of the child’s own welfare” (Dawkins, 2021).These are just a few examples, and as screening technology becomes cheaper, more companies will jump on the bandwagon of perfect “healthy” babies. Conversely, this creates a risk that parents come under pressure to terminate pregnancies with “imperfect babies” as I have experienced myself. What does this mean for people with rare diseases? From my personal moral perspective, the ethics are clear in cases where the pregnancy is clearly not viable. Yet, there are literally thousands of monogenic conditions and even chromosomal abnormalities, not all of which are lethal, and we are making constant strides in treating conditions that were previously considered untreatable. In addition, there is still societal prejudice against people with genetic disorders, and ignorance about how it is to live with a rare disease. In reality, however, all rare disease patients I have encountered are happy to be alive and here, even those whose conditions have significant impact on their quality of life. Many of us also don''t like the term “disorder” or “syndrome”, as we are so much more than merely a disorder or a syndrome.Unfortunately, I also see many parents panic about the results of prenatal testing. Without adequate genetic counselling, they do not understand that their baby’s condition may have actually a quite good prognosis without major impact on the quality of life. Following from this, a mere diagnosis of a rare disease – many of which would not even necessarily have been detectable until later in life, if at all – can be enough to make parents consider termination, due to social stigma.This of course raises the thorny issue of regulation, which range from the USA where there is little to no regulation of such screening technologies (ACOG, 2020), to Sweden where such screening technologies are banned with the exception of specific high‐risk/lethal medical conditions both parents are known carriers for (SMER, 2021). As countries come to grips with both the potential and the risks involved in new screening technologies, medical ethics board have approached this issue. And as screening technologies advance, we will need to ask ourselves difficult questions as a society. I know that in the world of “perfect babies” that some of these companies and individuals are trying to promote, I would not exist, nor would my daughter. I have never before had to find myself so often explaining to people that our lives have value, and I do not want to continue having to do so. Like other forms of diversity, genetic diversity is important and makes us richer as a society. As these screening technologies quickly advance and become more widely available, regulation should at least guarantee that screening must involve proper genetic counselling from a trained clinical geneticist so that parents actually understand the implications of the test results. More urgently, we need to address the problem of societal attitudes towards rare diseases, face the prejudice and fear towards patients, and understand that abolishing genetic diversity in a quest for perfect babies would impoverish humanity and make the world a much poorer place.  相似文献   

12.
Several genetic and nongenetic benefits have been proposed toexplain multiple mating (polyandry) in animals, to compensatefor costs associated with obtaining additional mates. The mostprominent hypotheses stress the benefits of increased geneticdiversity. In social insects, queens of most species mate onlyonce or have effective mating frequencies close to one. Yet,in a few species of ants, bees, and wasps, polyandry is therule. In these species, colonies are usually headed by a singlequeen, whereas multiple queening adds diversity in several ofthe remaining species, especially in ants. Here we investigatedmating frequency, inbreeding and relatedness between the queensand their mates in the polygynous ant Plagiolepis pygmaea, andthe effect of polyandry on the genetic diversity as a functionof the effective population size of individual colonies. Ourresults show that polyandry occurs frequently in the species.However, queens are frequently inseminated by close relatives,and additional sires add little genetic diversity among offspringof individual queens. In addition, the increase in diversityat the colony level is only marginal. Hence, contrary to establishednotions, polyandry in P. pygmaea seems not to be driven by substantialbenefits of genetic diversity. Nonetheless, very small or asyet unidentified genetic benefits to one party (males, workers,queens) in conjunction with low costs of mating may favor polyandry.Alternatively, nongenetic factors, such as convenience polyandry,may be more important than genetic factors in promoting polyandryin P. pygmaea.  相似文献   

13.
Many studies have focused on the importance of immigrants participating in the public spaces of the cities where they have settled in order to become integrated. Our research, in contrast, demonstrates the importance of contextualizing participation within the framework of the power relationships that justify and give meaning to certain practices of discipline and control. We look at one concrete example in Seville (Spain): the regulation of the Latin American sports leagues of San Jeronimo. This case demonstrates the central role of public space in monitoring and controlling immigrants and in the dynamics of resistance they develop.  相似文献   

14.
Populations of bluegill sunfish Lepomis macrochirus , experiencing heavy juvenile predation, showed increased growth rates and increased age and size at maturity relative to populations experiencing decreased predation on juveniles but increased predation on adults. This study examined bluegills experimentally from both types of populations and a cross between them in a common environment to determine if variation in growth and age at maturity is genetically or environmentally induced. Two factorial experiments, varying strain of bluegills and resource availability, were used to evaluate differences in growth rate. One experiment, varying strain of bluegills, was used to assess differences in age at maturity. Growth was strongly influenced by resource level, but growth rate did not vary among populations. Nearly all bluegills in each population matured at 1 year of age in a common environment. Thus, variation observed in source populations must be mostly attributable to differences in the environment between populations. At least three factors could potentially cause differences in growth and age at maturity: (1) variation in resource availability; (2) variation in demographic structure; and (3) variation in size-specific mortality rates caused by differences in predator abundance between populations. Observed patterns of variation between populations are best explained by effects of differences in predator populations.  相似文献   

15.
 A collection of 66 Malus×domestica Borkh. accessions from the USDA-ARS Plant Genetic Resources Unit’s core collection was screened with a set of eight SSR (simple sequence repeat) primers developed at the PGRU in order to determine genetic identities, estimate genetic diversity, and to identify genetic relationships among these accessions. All eight primer pairs generated multiple fragments when used in amplification reactions with DNA from these accessions. High levels of variation were detected with a mean of 12.1 alleles per locus and a mean heterozygosity across all eight loci of 0.693. The eight primer pairs utilized in this study unambiguously differentiated all but seven pairs of accessions in this collection of 66 M.×domestica Borkh. genotypes. The probability of matching any two genotypes at all eight loci in this study was approximately 1 in 1 billion. The markers detected two misnamed accessions in the collection. Genetic-identity data produced a genetic-relatedness phenogram which was concordant with geographic origins and/or known pedigree information. These SSR markers show great promise as tools for managing Malus ex situ germplasm collections as well as for collection and preservation strategies concerning wild Malus populations in situ. Received: 28 March 1998 / Accepted: 29 April 1998  相似文献   

16.
The Fisherian sexual selection paradigm has been called the null model of sexual selection. At its heart is the expectation of a genetic correlation (rG) between female preference and male trait. However, recent meta‐analysis has shown estimated correlations are often extremely weak and not statistically significant. We show here that systematic failure of studies to reject the null hypothesis that r= 0 is almost certainly due to the low power of most experimental designs used. We provide an easy way to assess experimental power a priori and suggest that current data make it difficult to definitively test a key component of the Fisher effect.  相似文献   

17.
Previous studies demonstrated the inhibitory participation of serotonergic (5-HT) and oxytocinergic (OT) neurons on sodium appetite induced by peritoneal dialysis (PD) in rats. The activity of 5-HT neurons increases after PD-induced 2% NaCl intake and decreases after sodium depletion; however, the activity of the OT neurons appears only after PD-induced 2% NaCl intake. To discriminate whether the differential activations of the 5-HT and OT neurons in this model are a consequence of the sodium satiation process or are the result of stimulation caused by the entry to the body of a hypertonic sodium solution during sodium access, we analyzed the number of Fos-5-HT- and Fos-OT-immunoreactive neurons in the dorsal raphe nucleus and the paraventricular nucleus of the hypothalamus-supraoptic nucleus, respectively, after isotonic vs. hypertonic NaCl intake induced by PD. We also studied the OT plasma levels after PD-induced isotonic or hypertonic NaCl intake. Sodium intake induced by PD significantly increased the number of Fos-5-HT cells, independently of the concentration of NaCl consumed. In contrast, the number of Fos-OT neurons increased after hypertonic NaCl intake, in both depleted and non-depleted animals. The OT plasma levels significantly increased only in the PD-induced 2% NaCl intake group in relation to others, showing a synergic effect of both factors. In summary, 5-HT neurons were activated after body sodium status was reestablished, suggesting that this system is activated under conditions of satiety. In terms of the OT system, both OT neural activity and OT plasma levels were increased by the entry of hypertonic NaCl solution during sodium consumption, suggesting that this system is involved in the processing of hyperosmotic signals.  相似文献   

18.
Polycelis nigra is a free-living simultaneous hermaphroditic flatworm that has amphimictic and pseudogamous parthenogenetic biotypes. Sexual individuals are always diploid (2n = 16) and pseudogamous parthenogens are polyploid (usually triploid). Two types of supernumerary chromosomes are found in parthenogens, those resembling autosomes ("A-like") and typical B chromosomes, both of which reach frequencies in populations of close to 100%. Experiments measuring the transmission rates of the B chromosomes indicated that they are potentially inherited via the male line, escaping expulsion by pseudogamous parthenogenesis. This study used the C-banding technique to demonstrate (i) that there is a single morphologically distinct B chromosome (B1) and (ii) that there are two "A-like" chromosomes that can be considered B chromosomes (B2 and B3) and which are not simple polysomics of one of the eight autosomes. As there is no genetic exchange between pseudogamous parthenogenetic lineages, two different individuals carrying a similar B morph must either have received it through common ancestry (a lineage marker) or have acquired it horizontally from another parthenogenetic lineage (leakage). C-banding further revealed intra-individual heteromorphy for band regions on chromosomes 5 and 8. This supports the karyotypic observation that oogenesis is preceded by premeiotic chromosome doubling followed by pairing of replicate homologues.  相似文献   

19.
Bovid species outnumber those of cervids by over two and half to one. The present study attempts to explain this difference using two principle concepts: contingency and constraint. The concept of contingency considers the role of biogeography and the distributions and timings of major dispersals seen in the two families. Although this historical context is considered vital for understanding the problem, cervids are also characterized by their global absence from open and arid grassland habitats. This is explained in terms of phylogenetic constraint. One proposal considers the deciduous antlers of cervids as constraining the group to higher quality forage that is not generally associated with open habitats. Alternatively and more generally applicable to all ruminants is the ‘cusp fusion hypothesis’, presented here for the first time. The hypothesis seeks to explain how the primitive ruminant molar state, as seen in modern cervids and giraffids, prevents the attainment of very high molar crowns and, with it, the ability to cope with high rates of dietary tooth wear. Conversely, the derived condition of precocial cusp fusion seen in the Bovidae and Antilocapridae has enabled higher tooth crowns, their expansion into open habitats, and an increased diversity potential. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 657–672.  相似文献   

20.
The main goal of synthetic biology (SB) is the creation of biodiversity applicable for biotechnological needs, while xenobiology (XB) aims to expand the framework of natural chemistries with the non‐natural building blocks in living cells to accomplish artificial biodiversity. Protein and proteome engineering, which overcome limitation of the canonical amino acid repertoire of 20 (+2) prescribed by the genetic code by using non‐canonic amino acids (ncAAs), is one of the main focuses of XB research. Ideally, estranging the genetic code from its current form via systematic introduction of ncAAs should enable the development of bio‐containment mechanisms in synthetic cells potentially endowing them with a “genetic firewall” i.e. orthogonality which prevents genetic information transfer to natural systems. Despite rapid progress over the past two decades, it is not yet possible to completely alienate an organism that would use and maintain different genetic code associations permanently. In order to engineer robust bio‐contained life forms, the chemical logic behind the amino acid repertoire establishment should be considered. Starting from recent proposal of Hartman and Smith about the genetic code establishment in the RNA world, here the authors mapped possible biotechnological invasion points for engineering of bio‐contained synthetic cells equipped with non‐canonical functionalities.  相似文献   

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