On Some Theoretical Studies on Gene Differentiation in Natural Populations

1975 ◽  
Vol 24 (1-2) ◽  
pp. 111-117
Author(s):  
Ranajit Chakraborty
Keyword(s):  
Genetic Variation ◽  
Genetic Drift ◽  
Molecular Level ◽  
Gene Diversity ◽  
Natural Populations ◽  
Simultaneous Action ◽  
Present Moment ◽  
Theoretical Studies ◽  
Random Genetic Drift ◽  
Approaches To Study

Different mathematical approaches to study the extent of genetic variation of natural populations are reviewed. The modern understanding of the gene structure permits new interpretations of existing concepts like fixation or inbreeding. A more recent measure of genie divergence, which at molecular level is designed to measure net codon differences is also seen to be related with gene diversity in a substructed population. It is argued that such variations are produced and preserved possibly by simultaneous action of migration, mutation, selection, and random genetic drift. At the present moment it is very difficult to isolate out the effect of each factor because of varying degrees of variation at the different gene sites and between different sets of populations.

scholarly journals RAPD ANALYSIS OF GENETIC VARIATION IN NATURAL POPULATIONS OF AEGILOPS SP. FROM SOUTH ADRIATIC

AGROFOR ◽  
2018 ◽  
Vol 3 (1) ◽  
Author(s):  
Miodrag DIMITRIJEVIĆ ◽  
Sofija PETROVIĆ ◽  
Borislav BANJAC ◽  
Goran BARAĆ
Keyword(s):  
Genetic Variation ◽  
Food Production ◽  
Rapd Markers ◽  
Rapd Analysis ◽  
Gene Diversity ◽  
Rapd Marker ◽  
Natural Populations ◽  
Genetic Structuring ◽  
Potential Source ◽  
Novel Approach

New challenges that food production is facing, requires novel approach inagricultural strategy. The scissors of growing demand for food and the limits of theEarth's resources are forcing plant breeders to run for the new borders, utilizing allthe available genetic variation in order to create fruitful and economically soundcultivars. Aegilops sp. (Poaceae) is a potential source of genetic variation for wheatimprovement. RAPD marker analysis was used in order to distinguish and evaluatedifferent genotypes of Aegilops sp. population samples from the collectiongathered during few years’ expeditions in South Adriatic, along the coastal, littoraland the inland parts of Montenegro. Ten randomly amplified polymorphic DNAmarkers (RAPDs) were tested: OPA-05, OPA-08, OPB-06, OPA-02, OPA-07,OPA-25, OPB-07, OPB-18, OPC-06, OPC-10 to examine genetic structuring on 18samples of 6 populations of different Aegilops sp. According to global AMOVA,75% of total gene diversity was attributable mostly to diversity within population(ΦPT =0.205 p=0.001), indicating that the groups of studied goat grass populationswere seemingly to differing genetically. In contrast, 25% of the variation camefrom variation among populations. According to PCoA, the distribution of 18 goatgrass accessions by Principal Coordinate Analysis shows 3 distinct groups. PCoaxis 1, PCo axis 2, and PCo axis 3 account for 20.8%, 18.2% and 14.1% of thevariation, respectively. The results showed that RAPD markers could be aconvenient tool for investigating genetic variation and for detecting geneticstructuring of populations. Genetic variability formed under natural selection wasentrenched.

The evolution of genetic diversity

1979 ◽  
Vol 205 (1161) ◽  
pp. 453-474 ◽  
Keyword(s):  
Genetic Diversity ◽  
Genetic Variation ◽  
Enzyme Kinetics ◽  
Genetic Control ◽  
Molecular Level ◽  
Natural Populations ◽  
Morphological Characters ◽  
Continuous Variation ◽  
Frequency Dependent ◽  
Frequency Dependent Selection

The existence within natural populations of large amounts of genetic variation in molecules and morphology presents an evolutionary problem. The ‘neutralist’ solution to this problem, that the variation is usually unimportant to the organisms displaying it, has now lost much of its strength. Interpretations that assume widespread heterozygous advantage also face serious difficulties. A resolution is possible in terms of frequency-dependent selection by predators, parasites and competitors. The evidence for pervasive frequency-dependent selection is now very strong. It appears to follow naturally from the behaviour of predators, from the evolutionary lability of parasites, from the ecology of competition and, at the molecular level, from the phenomena of enzyme kinetics. Such selection can explain the maintenance not only of conventional polymorphism but also of continuous variation in both molecular and morphological characters. It can account for the occurrence of diversity within groups of haploid and self-fertilizing organisms, and for the evolution of differences between individuals in their systems of genetic control.

scholarly journals The Population Genetics of Ploidy Change in Fungi

2020 ◽  
Author(s):  
Aleeza C. Gerstein ◽  
Nathaniel Sharp
Keyword(s):  
Population Genetics ◽  
Genetic Variation ◽  
Natural Selection ◽  
Genetic Variants ◽  
Natural Populations ◽  
Theoretical Work ◽  
Fungal Species ◽  
Random Genetic Drift ◽  
Lab Experiments ◽  
History Of

Ploidy is a significant type of genetic variation, describing the number of chromosome sets per cell. Ploidy evolves in natural populations, clinical populations, and lab experiments, particularly in fungi. Despite a long history of theoretical work on this topic, predicting how ploidy will evolve has proven difficult, as it is often unclear why one ploidy state outperforms another. Here, we review what is known about contemporary ploidy evolution in diverse fungal species through the lens of population genetics. As with typical genetic variants, ploidy evolution depends on the rate that new ploidy states arise by mutation, natural selection on alternative ploidy states, and random genetic drift. However, ploidy variation also has unique impacts on evolution, with the potential to alter chromosomal stability, the rate and patterns of point mutation, and the nature of selection on all loci in the genome. We discuss how ploidy evolution depends on these general and unique factors and highlight areas where additional experimental evidence is required to comprehensively explain the ploidy transitions observed in the field and the lab.

Random Genetic Drift in Small Populations

2020 ◽  
pp. 147-178
Author(s):  
Daniel L. Hartl
Keyword(s):  
Amino Acid ◽  
Allele Frequency ◽  
Genetic Drift ◽  
Diffusion Processes ◽  
Natural Populations ◽  
Small Populations ◽  
Random Genetic Drift ◽  
Diffusion Approximations ◽  
Sampling Formula ◽  
Allozyme Polymorphisms

Chapter 6 deals with the consequences of random genetic drift in finite populations and includes details of the diffusion approximations and their solutions as well as conditional diffusion processes. It includes probabilities of fixation and conditional times to fixation for neutral and nonneutral alleles. Various scenarios of mutation, migration, and selection are examined with regard to the stationary distributions of allele frequency. The Ewens sampling formula and its importance is discussed, as well as its implications for the distribution of the number of alleles in samples. An analysis of allozyme polymorphisms supports the hypothesis that most amino acid polymorphisms in natural populations are slightly deleterious.

scholarly journals Genetic variability of three natural populations of Maytenus aquifolium (Celesteraceae) from Telêmaco Borba, Paraná, Brazil

2010 ◽  
Vol 53 (5) ◽  
pp. 1037-1042 ◽  
Author(s):  
Sandra Aparecida Sahyun ◽  
Eduardo Augusto Ruas ◽  
Claudete de Fátima Ruas ◽  
Cristiano Medri ◽  
José Roberto Pinto de Souza ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Genetic Variability ◽  
Bayesian Analysis ◽  
Rapd Markers ◽  
Gene Diversity ◽  
Natural Populations ◽  
Soil Types ◽  
Number Of Clusters ◽  
Analysis Of Molecular Variance ◽  
Molecular Variance

Three populations of Maytenus aquifolium from Monte Alegre farm, Telemaco Borba county, Paraná, Brazil were analyzed by RAPD markers. A total of 13 primers were applied wich yielded 283 well amplified markers in all the studied populations (Mortandade, Vila Preta and Trinita), producing different values of gene diversity and polymorphic loci. The analysis of molecular variance (AMOVA) indicated that 21.77% of the genetic variation was among the population. Pairwise F ST analysis showed that the most divergent populations were closer geographically, demonstrating that other factors such as different soil types could explain this variation. Bayesian analysis for K number of clusters and the Principal Coordinate indicated that these three populations were highly structured, corroborating the high values found for the F ST and indicating that for conservation purposes all populations should be maintained.

scholarly journals Genetic Variation Among Natural Populations of Tilletia controversa and T. bromi

2000 ◽  
Vol 90 (4) ◽  
pp. 376-383 ◽  
Author(s):  
Guillermo Pimentel ◽  
Tobin L. Peever ◽  
Lori M. Carris
Keyword(s):  
Genetic Variation ◽  
Genetic Differentiation ◽  
Gene Diversity ◽  
Random Amplified Polymorphic Dna ◽  
Natural Populations ◽  
Host Population ◽  
Natural Hybridization ◽  
Character State ◽  
Phenotypic Analysis ◽  
Tilletia Controversa

Isolates of Tilletia controversa and T. bromi were sampled from wheat and two Bromus species hosts, respectively, in the Pacific Northwest, and genetic variation within and among populations was determined. Fifty-one random amplified polymorphic DNA markers from eleven primers were treated as phenotypic 1 and 0 character state data to estimate similarities and analyze molecular variance (AMOVA) among populations and as putative genetic loci to carry out analyses of gene diversity. Phenotypic analysis of T. controversa and T. bromi isolates revealed two distinct clusters that were 37% similar. The T. bromi cluster was subdivided further into two groups, corresponding to host, with 40% similarity. Cluster analysis based on allele frequencies produced similar results and also supported two T. bromi groups based on host. No evidence of natural hybridization and introgression was detected between the T. controversa and T. bromi populations. Both AMOVA and gene diversity analyses detected moderate levels of differentiation among T. controversa populations, whereas T. bromi populations were highly differentiated. The level of genetic differentiation observed between the T. bromi populations on different Bromus species hosts supports the hypothesis that a high degree of host specificity exists in the wild grass-infecting smuts. We speculate that the higher level of genetic differentiation among the T. bromi populations compared with the T. controversa populations on wheat may be due to selection by a more genetically diverse host population.

scholarly journals RAPD analysis of the genetic diversity of two natural populations of Paphiopedilum villosum var. Annamense rolfe. in the Lam Vien plateau

2016 ◽  
Vol 14 (3) ◽  
pp. 451-459
Author(s):  
Đặng Thị Thắm ◽  
Nông Văn Duy ◽  
Trần Văn Tiến ◽  
Lê Ngọc Triệu ◽  
Khuất Hữu Trung ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Wild Population ◽  
Gene Diversity ◽  
Species Conservation ◽  
Natural Populations ◽  
Small Population ◽  
Habitat Destruction ◽  
Similarity Coefficients ◽  
Population Sizes ◽  
Two Populations

Paphiopedilum villosum var. annamense Rolfe. is the attractive pot plant characterize by its larger and beautiful flower. Wild population of that orchid are now considered to be rare in nature as a result of habitat destruction and commercial preference. Thus, it is very important that actions should be taken to conserve this orchid before it becomes extinct. The information of genetic variation at both population and species levels is a scientific basic for species conservation. In this research, two populations of Paphiopedilum villosum var. annamense Rolfe were collected in Lam Dong province, Vietnam for analysing of genetic variation. RAPD directive was used to examine genetic variability in 20 individuals of two populations. The results showed that 25 bands were recorded from 12 specific identification primers. The percentages of polymorphic loci at species and population levels in the research were not high (Pt = 74.07%; P1 = 67.90%; P2 = 62.35%). However, in the first population, a higher percentage of polimorphic loci was observed as in the second one. Significant heterozygosity at both population and species levels was also low (HE1 = 0.23; HE2 = 0.18; and HEt = 0.25). The total gene diversity at the species level was partitioned primarily between two populations, as show by low GST= 0.17. Genetic distance between two populations was low (D12 = 0.079). In the orther hand, Genetic similarity coefficients between individuals in the general population were ranged from 0.57 to 0.91. The results suggested that the small population sizes in isolation had led to increase of inbred individuals within populations. Some solutions to the conservation and sustainable development have been mentioned.

Enzyme variation in natural populations of Sitka spruce (Piceasitchensis). 1. Genetic variation patterns among trees from 10 IUFRO provenances

1980 ◽  
Vol 10 (3) ◽  
pp. 415-422 ◽  
Author(s):  
Francis C. Yeh ◽  
Yousry A. El-Kassaby
Keyword(s):  
Genetic Variation ◽  
Gene Diversity ◽  
Natural Populations ◽  
Sitka Spruce ◽  
Genetic Distances ◽  
Pairwise Comparisons ◽  
A Value ◽  
Variation Patterns ◽  
Average Proportion ◽  
Geographic Sources

Genetic variation at 24 enzyme loci was studied for 10 IUFRO populations of Sitka spruce (Piceasitchensis (Bong.) Carr.). The average proportion of polymorphic loci per population was 0.51 ± 0.02 and the average proportion of heterozygous loci per individual was 0.15 ± 0.03. The following generalizations were advanced: (1) the amount of genetic polymorphism varied considerably from locus to locus; (2) many populations were similar in the amount and pattern of genetic variation for most loci; (3) but some loci had large differences among populations.Eight percent of the gene diversity was attributed to interpopulation differentiation; 92% of the total gene diversity resided within populations. Pairwise comparisons of genetic distances averaged 0.014, a value which reflected very little differentiation between geographic sources.

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