Biological Sciences
Gene Flow
Gene flow refers to the transfer of genetic material from one population to another through migration and interbreeding. It can lead to the spread of advantageous traits and genetic diversity within a species. Gene flow is a key factor in evolution, as it can influence the genetic makeup of populations and contribute to their adaptation to changing environments.
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9 Key excerpts on "Gene Flow"
eBook - PDF- Matthew B. Hamilton(Author)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
But, at the same time, genetic isolation allows subpo- pulations to evolve independent allele frequencies and maintain unique alleles as is required for genetic adaptation to local environments under natural selection, for example. It is worth noting that there are some important biological distinctions between Gene Flow and migration or dispersal. Migration (or dispersal) is simply the movement of individuals from one place to another. As such, migration may or may not result in Gene Flow. Gene Flow requires that migrat- ing individuals successfully contribute alleles to the mating pool of populations they join or visit. Thus, migration alone does not necessarily result in Gene Flow. Similarly, Gene Flow can also occur without the migration of individual organisms. Plants are a prime example, with Gene Flow that takes place via the movement of pollen grains (male gametes) but individuals themselves cannot migrate except as seeds. Gene Flow can also occur without easily detected migration of individuals, such as cases where individuals move briefly to mate and then return to their original geographic locations. To confuse matters, the variable m (for migration rate) is almost universally used to indicate the rate of Gene Flow in models of population structure. Even though models do not normally make the distinc- tion, it is wise to remember the biological differences between the processes of migration and Gene Flow in actual populations. 120 CHAPTER 4 Box 4.1 Are allele frequencies random or clumped in two dimensions? How can genetic variation in space be described to look for evidence of isolation by distance or other processes that cause spatial genetic differentiation in populations? The general approach is to compare pairs of individuals or populations, looking at both the similarity of their genotypes and how far apart they are located.
eBook - ePub- John H. Relethford(Author)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
This chapter includes a brief review of the basic concept and simple models of Gene Flow, applicable to a wide range of organisms. In addition, certain models used to analyze human Gene Flow are given particular focus, because it is often easier to assess Gene Flow in humans than in other organisms. I often see squirrels outside from my office window, but it is not easy to determine what part of campus they might have come from. Some probably live in the trees right across the road, but for all I know some might be migrants from farther away on campus or from someplace in the local neighborhood. How could I tell? In some studies of animal migration, they capture animals, tag them, and then recapture them later. Migration is much easier to assess in humans. Whereas we need to track squirrels, we can actually ask humans where they and their parents originated.Although we sometimes talk about migration and Gene Flow as synonymous, for many contexts we may need to draw a distinction. In humans, we typically treat migration as a change in residence as compared with a brief visit. For example, if I take a vacation trip to the Caribbean, we would not regard that as an actual migration, although if I moved to the Caribbean, that would constitute migration. The line between the two can sometimes be complicated; for example, a college student might live away from home most of the year, but this might not be considered a migration in many contexts. Gene Flow, on the other hand, involves the actual movement of genes (and DNA sequences) as the result of physically moving, whether temporarily or permanently. In this context, we can consider Gene Flow as what happens when an organism moves and reproduces in a different location, regardless of whether it remains there. In some cases, we might treat migration and Gene Flow as the same, but in other cases, the two terms may have different meanings.8.1 The Evolutionary Impact of Gene FlowOne assumption of Hardy–Weinberg equilibrium is that the population remains closed to other populations; that is, there is no Gene Flow. In fact, throughout our discussions of mutation, drift, and selection, we have always focused on a single population. In the real world, however, the existence of a single-population species is very rare. For example, humans live in thousands of populations around the world, which are all interconnected by varying levels of Gene Flow in the present and the past. What is the evolutionary impact of Gene Flow?
eBook - PDF- Joanna R. Freeland(Author)
- 2020(Publication Date)
- Wiley(Publisher)
197 Molecular Ecology, Third Edition. Joanna R. Freeland. © 2020 John Wiley & Sons Ltd. Published 2020 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/freeland/molecularecology 6 Why Study Multiple Populations? In Chapter 5 we learned that by quantifying the genetic diversity of single populations, we can gain considerable insight into processes as diverse as bottlenecks, reproduction, and natural selection. We must understand these process before we can interpret genetic data in an ecological context, but the genetics of populations are influenced by both intrapopulation and interpopulation processes, and therefore the next step is for us to investigate how Gene Flow (the transfer of genes from one population to another) also influences the evolution of populations and species. We will start this chapter by looking at how we can quantify population subdivision and Gene Flow between defined populations, and between non‐a priori populations. We will then ask the question of how local adaptation occurs in the presence of ongoing Gene Flow by looking at the ways in which genetic drift and natural selection interact with Gene Flow to influence the genetic structure of populations across a species’ range. What is Gene Flow? Before looking at ways to quantify Gene Flow, we have to understand exactly what con- stitutes Gene Flow, and how it differs from dispersal and migration. Dispersal generally refers to the movement of individuals or propagules between discrete locations or popu- lations, whereas migration refers to periodic movement to and from a specific geograph- ical area, often occurring seasonally and along a consistent route. While either dispersal or migration must precede Gene Flow, neither result in Gene Flow unless individuals suc- cessfully reproduce once they have arrived at their new location.
eBook - ePub- Andrew P. Hendry(Author)
- 2016(Publication Date)
- Princeton University Press(Publisher)
Chapter 5 Gene FlowIn the previous chapter, I outlined adaptive divergence as the primary determinant of population and species differences and therefore their divergent eco-evolutionary effects. It might have sometimes seemed I was arguing that adaptive divergence was ubiquitous and all powerful whereas, in reality, the success of adaptive divergence will depend critically on several factors. In the present chapter, I will focus on one of those factors: Gene Flow—the extent to which diverging groups are connected by genetic exchange. Gene Flow can have a diversity of effects that will be discussed in detail below but the most obvious effect, by way of example, is its role in preventing the independent evolution of populations in different environments and thereby constraining their adaptive divergence (Lenormand 2002, Garant et al. 2007). Through this constraint, Gene Flow can also prevent speciation and therefore adaptive radiation (Felsenstein 1981). For these reasons, the effects of adaptive divergence on eco-evolutionary dynamics will be shaped and modified by Gene Flow.I start with a consideration of what, precisely, Gene Flow is, including in relation to “dispersal” and “migration.” I then discuss how Gene Flow is commonly measured and interpreted in nature. I go on to explain the diversity of effects, both positive and negative, that Gene Flow can have on adaptive divergence. I then review—through the usual “key” questions—empirical evidence for the effects of Gene Flow on adaptive divergence, speciation, demography, and species’ ranges.What are migration, dispersal, and Gene Flow?These terms have been used in a variety of ways by a variety of authors (Endler 1977, Dingle 1996, Neigel 1997, Lenormand 2002, Garant et al. 2007). Instead of attempting to declare and defend some “correct” definitions, I will simply state definitions used consistently in the present book. Bear in mind that other publications sometimes use the same or different terms in similar or different ways.
- K.V. Chaitanya(Author)
- 2022(Publication Date)
- CRC Press(Publisher)
These are the following forces Mutations The frequency of gene B and its allele b will not remain in Hardy-Weinberg equilibrium if the mutation rate of B > b or b > B changes. Critically, this type of mutation plays only a minor role in the evolution, and the rates are too low. However, both gene and whole genome duplication is a form of mutation, which might have played a significant role in the evolution of new alleles. After being shuffled in various combinations with the rest of the gene pool, they provide the raw material for natural selection. Gene Flow Most of the species are made up of local populations, whose members tend to breed within the same population group. Breeding among the local populations might lead to developing a gene pool that is distinct from other local populations. Breeding between the members of one population group with occasional immigrants from the adjacent population can introduce new genes or even alter the existing gene frequencies among the residents. In many plants and some animals, Gene Flow can also occur between different species, known as hybridization. Breeding these hybrids with either of the parents will lead to the entry of new genes into the gene pool of the parent population. This process is known as introgression. In either case, Gene Flow increases the variability of the gene pool. Genetic Drift Most of the interbreeding is limited to the members of local population groups. Chance alone can eliminate certain members out of proportion to their numbers in a population. In such cases, the frequency of an allele may begin to drift toward higher or lower values, ultimately representing 100% of the gene pool, or just disappear from it. Drift produces evolutionary change, but there is no guarantee that the new population will fit better than the original one
eBook - PDF- Tomar, Arun Kumar(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
This leads to differentiation of gene frequencies in local populations resulting from sampling and is known as random drift . The fourth activity of breeders is the trade breeding under which the animals are sold or transferred to another breeder’s herd and thus migration of animals occurs. Moreover, the advances in animal breeding due to artificial in semi nation and frozen semen technology have made possible the transportation of semen from one herd to another herd located far apart with in or outside the country. This has thus further increased the possibility of Gene Flow ( migration ) from one corner to other corner of the country or the world. (ii) Role of Nature to Change Genetic Structure The factors which are under the control of nature to upset the genetic equilibrium are the mutation (change in genetic structure of a gene) and the natural selection . The gene mutation occurs due to many factors and changes the genetic material(mutation and chromosomal aberrations). The natural selection operates through differential fertility and viability. The fertility and survivability of individuals results in non-random mating and selective breeding. 2. Second Criterion Factors involved at individual and population level: The first is the change at gene level(mutation). The second is the change at population level by Gene Flow (migration), selection, small population size, and by a change in mating system from random matingtopreferentialmating (non-random mating). This ebook is exclusively for this university only. Cannot be resold/distributed. 3. Third Criterion Type of change involved : The genetic change may be brought in genotype distribution without affecting the gene frequencies or the change may occur in gene frequencies which accompanied change in genotype frequencies. The first category of force is the non-randommating (genetic assortative mating) which leads to a change only in genotype frequencies without affecting the gene frequencies.
eBook - PDF- Dick Neal(Author)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
13.6 ESTIMATING Gene Flow It is extremely difficult to quantify gene flow between subpopulations or within large popula- tions with continuous distributions. If we use direct methods, where the movements of marked 196 Migration, Gene Flow and Differentiation of Populations Table 13.1 Calculation of F-statistics at three hierarchical levels of grouped samples of Linanthus parryae in the Mohave Desert (see text) Region Subregions Regions Total Blue allele frequency HS Average allelic frequency HR Average allelic frequency HT West (7) 0.430 0.4902 0.452 0.4954 0.256 0.3809 0.297 0.4176 0.003 0.0060 0.241 0.3658 0.268 0.3924 0.2781 0.4016 Mid-west (8) 0.001 0.0020 0.001 0.0020 0.000 0.0000 0.001 0.0020 0.001 0.0020 0.000 0.0000 0.000 0.0000 0.000 0.0000 0.0005 0.0010 Mid-east (7) 0.001 0.0020 0.000 0.0000 0.001 0.0020 0.000 0.0000 0.000 0.0000 0.000 0.0000 0.002 0.0040 0.0006 0.0011 Estimating Gene Flow 197 individuals are tracked, we risk confusing migration with gene flow (see chapter introduction). Therefore, we also need to track the reproductive success of the individuals that move from one location to another. Such studies are laborious and difficult to do well. For example, gene flow in flowering plants occurs by the movement of both male gametes (pollen) and seeds, and so an investigator may need to study the behaviour of a pollinator (e.g. insect, bird or mammal) and the efficiency of pollen transfer as well as track the fate of thousands of seeds and the efficiency of their germination. Such studies may provide estimates over a short time scale, and this may be sufficient if we are only interested in assessing current gene flow. However, if we are interested in understanding the genetic make-up of populations, we should be aware that gene flow probably varies considerably over time. For example, a subpopulation of a territorial species that has declined in density for some reason may have an increased likelihood of immigration and subsequent gene flow than before.
eBook - PDF- John A. Thomas, Roy L. Fuchs(Authors)
- 2002(Publication Date)
- Academic Press(Publisher)
Chapter 15 Gene Flow from Transgenic Plants Mike Wilkinson Department of Agricultural Botany, Plant Sciences Laboratories Reading, United Kingdom Introduction Transgene Spread Initial Hybrid Formation Conclusion Transgene Introgression References Transformation technology o V ers unprecedented opportunities for the im-provement of crops. At the same time, there is concern that the use of these plants may lead to unwanted change to the broader environment. Gene ¯ow from genetically modi®ed GM) crops is perhaps the most apparent route by which such change could be mediated and has been the subject of intense study. There are essentially four sorts of recipient destination into which a transgene might move by gene ¯ow: ®elds of non-GM cultivars, feral popula-tions of the crop, conspeci®c weeds or wild populations, and populations of a related species. The process of gene ¯ow can itself be broken down into several components to form an interdependent pathway of intermediate stages. Examples are used to illustrate our current state of knowledge of three key stages in the phenomenon: the formation of a F 1 hybrid, gene stabilization by introgression, and transgene spread to other populations. The likelihood of completing the pathway so that a transgene becomes widespread and leads to some form of environmental change is dependent on a complex array of factors. These include characteristics of the crop and the transgene, the geographical location and the size, proximity, and the biology of the recipient. Biotechnology and Safety Assessment, 3rd edition Copyright 2002, Elsevier Science USA). All rights reserved. 413 In attempting to quantify the risks posed by a particular transgene±crop± location combination, a progressive stepwise approach is therefore advo-cated.
eBook - ePub- Matthew Hamilton(Author)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
CHAPTER 4: Population structure and Gene Flow 4.1 Genetic populations- Genetic versus geographic organization of populations.
- Isolation by distance and divergence of populations.
- Gene Flow and migration.
- Direct and indirect measures of Gene Flow.
The expectation that genotypes will be present in Hardy–Weinberg frequencies, covered in detail in Chapter 2, depends on the assumption of random mating throughout a population. Implicit is the view that a population is a single entity where processes such as mating and movement of individuals are uniform throughout, a condition often called panmixia. Several processes and features at work in actual populations make this initial perspective of population uniformity unlikely to hold true for many populations. It is often the case that within large populations the chances of mating are not uniform as assumed by Hardy–Weinberg. Instead, the chance that two individuals mate often depends on their location within the population. This leads to what is called population structure, or heterogeneity across a population in the chances that two randomly chosen individuals will mate. The first section of this chapter will introduce biological phenomena that contribute to population structure in mating and migration that can lead to differences in allele and genotype frequencies in different parts of a population. The goal of the entire chapter is to develop expectations for the impact of population structure on genotype and allele frequencies along with methods to measure patterns of population structure.To get an initial idea of how a population might be divided into smaller units that behave independently, consider the hypothetical population in Fig. 4.1 . Initially, all individuals in the population have equal chances of mating regardless of their location. Since mating is random, genotype frequencies in the entire population match Hardy–Weinberg expectations and allele frequencies are equal on both sides of the creek. Then imagine that the creek bisecting the population changes permanently into a large river that serves as a barrier to movement of individuals from one side to the other side. Although some individuals still cross the river on occasion, the rate of genetic mixing or Gene Flow between the two subpopulations bisected by the river is reduced. Lowered levels of Gene Flow mean that the two subpopulations have allele and genotype frequencies that tend to be independent through time. At the later time points in Fig. 4.1 , the two subpopulations have increasingly different allele frequencies over time due to genetic drift, even though there are Hardy–Weinberg expected genotype frequencies within each subpopulation. In the last time period in Fig. 4.1 , the allele frequencies in the subpopulations separated by the river are quite different and the genotype frequencies in the total population no longer meet Hardy–Weinberg expectations. In this example, a reduction in Gene Flow allows the two subpopulations to be acted on independently by genetic drift, ultimately resulting in population differentiation of allele frequencies. The appearance of a geographic barrier that restricts Gene Flow among populations like that in Fig. 4.1 is sometimes called a vicariance
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