Biological Sciences
Genetic Diversity
Genetic diversity refers to the variety of genetic information within a population or species. It encompasses the range of different alleles, genes, and genetic traits present in a group of organisms. Genetic diversity is important for the long-term survival and adaptability of a population, as it provides the raw material for evolution and allows species to respond to environmental changes.
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9 Key excerpts on "Genetic Diversity"
- Mahmut Caliskan(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
Part 1 Genetic Diversity in Plant Populations 1 Genomics Meets Biodiversity: Advances in Molecular Marker Development and Their Applications in Plant Genetic Diversity Assessment Péter Poczai 1,2 , Ildikó Varga 2 , Neil E. Bell 1,3 and Jaakko Hyvönen 1 1 Plant Biology, University of Helsinki, Helsinki 2 Department of Plant Science and Biotechnology, Georgikon Faculty University of Pannonia, Keszthely 3 Botanical Museum, University of Helsinki, Helsinki 1,3 Finland 2 Hungary 1. Introduction Genetic Diversity is the fundamental source of biodiversity – the total number of genetic characters contributing to variation within species. In other words it is the measure that quantifies the variation found within a population of a given species. Genetic Diversity among individuals reflects the presence of different alleles in the gene pool, and hence different genotypes within populations. Genetic Diversity should be distinguished from genetic variability, which describes the tendency of genetic traits found within populations to vary (Laikre et al., 2009). Since the beginning of the 20 th century, the study of Genetic Diversity has been the major focus of core evolutionary biology. The theoretical metrics developed, such as genetic variance and heritability (Fisher, 1930; Wright, 1931), provided the quantitative standards necessary for the evolutionary synthesis. Further research has focused on the origin of Genetic Diversity, its maintenance and its role in evolution. Simple questions such as “who breeds with whom” initiated studies on the relatedness of populations. These investigations led to the formation of metapopulation theory, where a group of spatially separated populations of the same species interact at some level and form a coherent larger group (Hanski, 1998). The discovery of spatial structure in populations was a key element in the early concepts and models of population ecology, genetics and adaptive evolution (Wright, 1931; Andrewartha & Birch, 1954).
eBook - PDF- K V Krishnamurthy(Author)
- 2003(Publication Date)
- CRC Press(Publisher)
2 Genetic Diversity Introduction In the last chapter it was recorded that Biodiversity can be studied at four levels: Gene, Species, Ecosystem and Landscape. In this chapter attention will be focused on details of Genetic Diversity, which is also referred to as within-species divemity, or intra-or infra-specific divemity. A number of infra-specific categories have often been recognised and most of them also enjoy taxonomic implications without necessarily being defined in genetic terms (UNEP 1995): subspecies, varieties, land races, clines, cultivars, ecotypes, chemotypes, cytotypes, hybrids, polytypes, polyploid complexes, aggregated species, etc. The recognition of these 'taxonomic' categories often poses problems in defining and conceptualizing Genetic Diversity. It should thus be emphasised that 'there is no single definition of Genetic Diversity that can be used for all purposes' (UNEP 1995, p. 213). Nature and Origin of Genetic Variations It is a well-known fact that the blueprints for all living beings are genes and that they consist of discrete segments of deoxyribonucleic acid (DNA). Meadows (1990) was correct in making the following remark: 'Nature's knowledge is contained in the DNA within living cells'. DNA is a linear molecule composed of sequences of four different nucleotide bases: adenine, guanine, thymine and cytosine. These four bases form the four base pairs: adenine-thymine, guanine-cytosine, thymine-adenine and cytosine-guanine. Genes are 'linearly arranged' along the length of the DNA molecule. All observed variations are invariably due to variations in the sequences of the four base pairs of the DNA molecule. The number of possible combinations of these base pairs exceeds the number of atoms in the universe. From this, one can imagine the magnitude of variations that can be produced. The combinations of these four base pairs in various permutations result in the Genetic code.
eBook - PDF- Christian Lévêque, Jean-Claude Mounolou(Authors)
- 2004(Publication Date)
- Wiley(Publisher)
3 . 2. 5 Spatial organization and dynamics of intraspecific Genetic Diversity Genetic Diversity is the fruit of the history of the DNA molecules present on the planet today. It is distributed geographically over all the species inhabiting the different ecosystems. The developmental and reproductive strategies of each species, population and individual mould this Genetic Diversity both qualitatively, quantitatively and over time. Theoretically, in the absence of any intrinsic or extrinsic constraints, all genes and all DNA molecules are equally prone to replication. Under such conditions, Genetic Diversity is preserved from one generation to another and, in the absence of mutations, remains identical onto itself. The pattern of diversity observed in a site remains stable, characterized by the frequency of the various alleles present in the area. Thus, for sexually reproductive plant and animal species, mitosis and meiosis are dependable and accurate systems for splitting DNA molecules, independ- ently of the nature and volume of information carried by these molecules. 3 . 2 ORIGINS AND DYNAMICS 47 The laws of genetics revolutionized biology in the 20th century. They are quantitative and predictive and may be tested experimentally by compar- ing actual observations with the theoretical predictions of a mathemat- ical model. This applies to Mendel’s laws on the scale of individuals, as well as to the Hardy–Weinberg law on the scale of populations. (The latter law predicts that for any population, the nature and frequency of genotypes will remain constant from one generation to the next, provided all encounters between gametes of the previous generation are equally probable – a situation known as panmixia.) Given a large population, its Genetic Diversity should be preserved over successive generations.
eBook - ePub- Peerzada Arshid Shabir, Peerzada Yasir Yousuf, Khalid Rehman Hakeem, Peerzada Arshid Shabir, Peerzada Yasir Yousuf, Khalid Rehman Hakeem(Authors)
- 2022(Publication Date)
- Apple Academic Press(Publisher)
Diederichsen and Richards, 2003 ). This facilitates the conservation of trait-specific genotypes/accessions that can be used in crop improvement by following conventional and non-conventional approaches.Biodiversity is the repository that offers an opportunity to meet our food and nutritional requirements sustainable by maintaining natural genetic variation at intra- and interspecific levels in the biological systems. The main aim of conserving genetic variability is to improve the social and economic status of poor people to meet their food and nutritional requirements and at the same time keeping their cultural diversity intact. There is an unequal distribution of biological resources and thus the countries should collaborate for effective conservation and utilization at a global level (Rao and Hodgkin, 2002 ). Assessment of population structure and genetic variability in rare and endangered plant species is of vital importance for the development of conservation and management strategies because it provides valuable insights into the demography, reproduction, and ecology of species (Zaya et al., 2017 ).10.2 FACTORS RESPONSIBLE FOR Genetic Diversity
The extent of variation observed within and among the individuals/genotypes/accessions of a population or species is defined as Genetic Diversity (Brown, 1983 ). It depends on some important factors which include the presence of different forms of a gene (alleles) among individuals, their interaction, distribution, and the influence they have on performance and total variation presented by the individuals of a population/species. This total variation is determined by the frequency of mutation and recombination. Other factors include selection, genetic drift, and the amount of gene flow in different populations that cause the variation in the population (Brown, 1988 ; Hamrick et al., 1992
eBook - PDF- W. Johnny Wilson, Richard Primack(Authors)
- 2019(Publication Date)
- Open Book Publishers(Publisher)
Figure 3.4 Genetic Diversity arises due to variation in the alleles of individual genes and variation in chro-mosomes from different parents, which give rise to genetic variation between individuals, both within the same population and between different populations. CC BY 4.0. In species which reproduce asexually, the potential for increased Genetic Diversity is limited to DNA mutations. However, sexual reproduction creates new genetic combinations by bringing together chromosomes from each parent. This process, called recombination, results in offspring that are genetically unique from their parents. Genetic mutations provide the foundation of genetic variation, but sexual reproduction dramatically increases Genetic Diversity by randomly mixing alleles in different combinations. Two factors determine a species’ Genetic Diversity: the number of genes that have multiple alleles ( polymorphic genes) and the number of alleles present in a population for each polymorphic gene. If a gene is polymorphic, some individuals will have two different forms of the gene—that is, they will be heterozygous because they received different alleles of the same gene from their parents. Some individuals will have two of the same forms of the Genetic Diversity enables species to adapt to environmental change. 69 Chapter 3 | What is Biodiversity? gene—they will be homozygous because each parent gave them the same allele. In general, the greater the Genetic Diversity in a population, especially the greater number of alleles present, the more capable a species will be to adapt to changing circumstances in their environment. Genetics also affect an individual organism’s development, physiology, and fitness —the relative ability of individuals to survive and reproduce. This same principle gives humans the ability to select and breed crops and domestic animals with characteristics that benefit the production and quality of food (Davis et al., 2012).
eBook - ePubBiotechnology and Plant Breeding
Applications and Approaches for Developing Improved Cultivars
- Aluízio Borém, Roberto Fritsche-Neto(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
Studies about Genetic Diversity have been of great importance for the purposes of genetic improvement and to evaluate the impact of human activity on biodiversity. They are equally important in the understanding of the microevolutionary and macroevolutionary mechanisms that act in the diversification of the species, involving population studies, as well as in the optimization of the conservation of Genetic Diversity. They are also fundamental in understanding how natural populations are structured in time and space and the effects of anthropogenic activities on this structure and, consequently, on their chances of survival and/or extinction. This information provides an aid in finding the genetic losses generated by the isolation of the populations and of the individuals, which will be reflected in future generations, allowing for the establishment of better strategies to increase and preserve species diversity and diversity within the species.Genetic resources are established by accesses that represent the genetic variability organized in a set of different materials called germplasm. They comprise the diversity of genetic material contained in old, obsolete, traditional, and modern varieties, wild relatives of the target species, wild species and primitive lines, which can be used in the present or in the future, for food, agriculture, and other purposes.The most important causes of loss of biodiversity and of genetic resources are: the destruction of habitats and natural communities; genetic vulnerability; genetic erosion; and genetic drift. The Genetic Diversity of the species is an important way to maintain the natural capacity to respond to climatic changes and all types of biotic and abiotic stress. In actuality, there exists great concern in evaluating biodiversity, because of the marked loss of Genetic Diversity, mostly due to the actions of man, replacing local varieties with modern varieties, hybrids, and, most recently, clones, so that large expanses of area are occupied by one or a few varieties or narrow genetic base.
eBook - ePub- Frank W. Nicholas(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
ex-situ conservation by storage of gametes or zygotes. However, this form of technology is available for only a very limited range of species. As also with domesticated species, cloning from differentiated cells offers a longer-term prospect.Summary- If a population can be genotyped for some DNA markers, its level of Genetic Diversity can be estimated as observed heterozygosity, expected heterozygosity, allelic diversity, and effective number of alleles
- The genetic distance between two populations is the extent to which their allelic frequencies differ
- The Genetic Diversity between two populations can also be estimated by counting the number of bases at which the sequence of a particular locus differs between the two populations
- Each of the above measures of Genetic Diversity among populations is typically estimated for all pairwise combinations of a set of populations (breeds or isolated populations or species), from which it is possible to construct a phylogenetic tree, showing the relationship of each population to every other population
- Genetic Diversity is important because it is the only means by which populations can immediately respond to selection (artificial and/or natural) either now or when circumstances change in the future
- The biggest threat to Genetic Diversity in livestock species in recent times has been selection between breeds
- For non-domesticated species, the main threat to Genetic Diversity is human encroachment
- To maintain around 90 per cent of a population’s Genetic Diversity for 100 years, the effective population size must be around 500/L ; and to retain evolutionary potential in the longer term (where generation intervals are not relevant), an effective population size of at least 500 is required
- Captive breeding programmes conducted by zoos and other organizations are good examples of the practical application of population and quantitative genetics
Further readingBoakes, E.H., Wang, J. and Amos, W. (2007) An investigation of inbreeding depression and purging in captive pedigreed populations. Heredity , 98
eBook - PDFTechnological Change In Agriculture
Locking in to Genetic Uniformity
- D. Hogg(Author)
- 2000(Publication Date)
- Palgrave Macmillan(Publisher)
1 Genetic Diversity in Agriculture: Its Rise, Fall and Significance The rise and fall of Genetic Diversity in agriculture The development of diversity For more than ten thousand years, human beings have sought to trans- form their environment to ensure that their basic food requirements are met. Through agriculture, societies have directed the evolutionary process of animals and crops. 1 The criteria for selection of crop and animal varieties for agricultural purposes substantially changes the selection pressures to which these organisms are exposed. Few domest- icated crops would survive in the absence of human husbandry or cul- tivation. 2 They have been adapting to, and have been selected for their suitability in, agricultural systems which have changed over time in their rationale, geographical extent and location. Agricultural crops (and livestock) co-evolve with humans. 3 It is worth considering what conditions are necessary in order for crops to adapt to changed socio-economic and environmental condi- tions. Natural selection in ‘the wild’ requires that there be diversity on which selection pressures can act. The process of selection imparts to adaptation a genetic, and therefore heritable, base. 4 Those combina- tions that are selected will constitute the best part of the genetic make- up of subsequent generations, resulting in the development of ecotypes adapted to local ecological conditions. Ecotypes are made up of popu- lations which are not uniform genetically, but are characterised by the frequency with which different alleles of genes occur within that popu- lation (Holden et al. 1993, 28; Simmonds 1979, ch. 1). Changes in environmental conditions can be catastrophic for a given ecotype lacking the diversity necessary for adaptation. In most wild plants, a degree of diversity is maintained within the ecotype through 1
eBook - PDF- Torbjörn Säll, Bengt O. Bengtsson(Authors)
- 2017(Publication Date)
- Wiley-Blackwell(Publisher)
Derivation 5 The evolution of Genetic Diversity The derivations in this chapter continue to describe the effect of biolog-ical populations being finite in size, even if potentially large in number. We start by finding the formula for how much genetic variation is expected in a diploid population where both mutation and genetic drift operate. The same population model is assumed as in the last chapter – the simple and well-defined Wright–Fisher model – though it is here used for going forward rather than backward in generations. We then extend our results by investigating how long it takes for a population to build up its standing genetic variation, and for how long the variation in a population will ‘remember’ a prior demographic disturbance to its current size. In our derivations, we assume that every new mutation leads to a new allelic type. The biological background to this assumption is discussed at the end of the chapter, where we introduce the infinite sites model of genes and DNA stretches. Within the framework of this model, it is possible to analyse gene copies, not only with respect to them being dif-ferent or not, but from the point of view of how different they are. When such information is available, powerful phylogenetic reconstructions can be made, and we sketch the basis for such work. We also discuss how sequence information can be used to test the processes that have led to the currently existing genetic variation in a population: Is the variation affected solely by random processes, or is there an indication that, for example, selection has also been involved? The chapter finishes with a brief comment on the versatility of methods with which population genetic equations can be analysed. Understanding Population Genetics , First Edition. Torbjörn Säll and Bengt O. Bengtsson. © 2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd. [ 85 ]
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