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In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. Foundations of modern biology There are five unifying principles eVolution is the third Album by eLDee, it was due to be released in 2008 An adaptation is a characteristic of an Organism that has been favored by Natural selection and In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Speciation is the Evolutionary process by which new biological Species arise The wide range of evidence of common descent of living things strongly indicates the occurrence of Evolution and provides a wealth of information on the natural processes Although evidence of early Life is scarce and often difficult to interpret it appears that life appeared on Earth relatively soon (on the Geologic time scale) after Evolutionary thought, the idea that species change over time has roots in antiquity in the ideas of the Greeks, Romans, Chinese and Muslims theory of transmutation had early origins in the speculations and hypotheses of Erasmus Darwin, and Jean-Baptiste Lamarck. Objections to evolution have been raised ever since various evolutionary ideas came to prominence around the start of the nineteenth century Cladistics is the hierarchical classification of Species based on evolutionary ancestry Ecological genetics is the study of Genetics in the context of the interactions among organisms and between the organisms and their environment Evolutionary developmental biology ( evolution of development or informally evo-devo) is a field of Biology that compares the developmental processes Human evolution, or anthropogenesis, is the part of biological Evolution concerning the emergence of Homo sapiens as a distinct Species Molecular evolution is the process of evolution at the scale of DNA, RNA, and Proteins Molecular evolution emerged as a scientific field in the 1960s as Population genetics is the study of the Allele frequency distribution and change under the influence of the four evolutionary forces Natural selection, Genetic Population genetics is the study of the Allele frequency distribution and change under the influence of the four evolutionary forces Natural selection, Genetic An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance In Biology a population is the collection of inter-breeding organisms of a particular Species; in Sociology

Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Allele frequency is a measure of the relative frequency of an Allele at a genetic place(locus in a Population. Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population. In Population genetics, a gene pool is the complete set of unique Alleles in a Species or Population.

There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, as greater mobility of an individual tends to give it greater migratory potential. Animals tend to be more mobile than plants, although pollen and seeds may be carried great distances by animals or wind.

Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. It is for this reason that gene flow strongly acts against speciation, by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species. Speciation is the Evolutionary process by which new biological Species arise

Example: If a field of genetically modified corn is grown alongside a field of non-genetically modified corn, pollen from the former is likely to fertilize the latter.

Contents 1 Barrier to gene flow 2 Gene flow in humans 3 Gene flow between species 3.1 Genetic pollution 4 Models of gene flow 5 Gene flow mitigation 6 See also 7 External links 8 References

Barrier to gene flow

Physical barriers to gene flow are usually, but not always, natural. They may include impassable mountain ranges, oceans, or vast deserts. In some cases, they can be artificial, man-made barriers, such as the Great Wall of China, which has hindered the gene flow of native plant populations^[1]. The Great Wall of China ( or ( is a series of stone and earthen Fortifications in China, built rebuilt and maintained between the 6th century BC and the 16th Samples of the same species which grow on either side have been shown to have developed genetic differences, because there is no gene flow to provide recombination of the gene pools.

Barriers to gene flow need not always to be physical. Species can live in the same environment, yet show very limited gene flow due to limited hybridization or hybridization yielding unfit hybrids.

Gene flow in humans

Gene flow has been observed in humans. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus For example, in the United States, gene flow was observed between a white European population and a black West African population, which were recently brought together. The United States of America —commonly referred to as the In West Africa, where malaria is prevalent, the Duffy antigen provides some resistance to the disease, and this allele is thus present in nearly all of the West African population. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including The Duffy antigen is a protein located on the outside of Red blood cells and is named after the patient in which it was discovered In contrast, Europeans have either the allele Fy^a or Fy^b, because malaria is almost non-existent. By measuring the frequencies of the West African and European groups, scientists found that the allele frequencies became mixed in each population because of movement of individuals. It was also found that this gene flow between European and West African groups is much greater in the Northern U. S. than in the South.

Gene flow between species

Gene flow can occur between species, either through hybridization or gene transfer from bacteria or virus to new hosts. In Biology, hybrid has two meanings The first meaning is the result of interbreeding between two animals or plants of different taxa.

Gene transfer, defined as the movement of genetic material across species boundaries, which includes horizontal gene transfer, antigenic shift, and reassortment is sometimes an important source of genetic variation. Antigenic shift is the process by which at least two different strains of a virus (or different viruses especially Influenza, combine to form a new subtype Reassortment is the mixing of the genetic material of two similar Viruses that are infecting the same cell Viruses can transfer genes between species [2]. Bacteria can incorporate genes from other dead bacteria, exchange genes with living bacteria, and can exchange plasmids across species boundaries [3]. A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA "Sequence comparisons suggest recent horizontal transfer of many genes among diverse species including across the boundaries of phylogenetic "domains". History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes. " [4]

Biologist Gogarten suggests "the original metaphor of a tree no longer fits the data from recent genome research". Biologists [should] instead use the metaphor of a mosaic to describe the different histories combined in individual genomes and use the metaphor of an intertwined net to visualize the rich exchange and cooperative effects of horizontal gene transfer. [5]

"Using single genes as phylogenetic markers, it is difficult to trace organismal phylogeny in the presence of HGT [horizontal gene transfer]. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Combining the simple coalescence model of cladogenesis with rare HGT [horizontal gene transfer] events suggest there was no single last common ancestor that contained all of the genes ancestral to those shared among the three domains of life. Cladogenesis is an evolutionary splitting event in which each branch and its smaller branches forms a " clade " an evolutionary mechanism and a process of adaptive evolution A Last Common Ancestor (LCA is the Most recent common ancestor of any two Clades for example species that came to be separated by a Species barrier Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism Each contemporary molecule has its own history and traces back to an individual molecule cenancestor. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The last universal ancestor ( LUA) also called the last universal common ancestor ( LUCA) the cenancestor or "number one" However, these molecular ancestors were likely to be present in different organisms at different times. " [6]

Genetic pollution

Main article: Genetic pollution

Purebred, naturally-evolved, region-specific, wild species can be threatened with extinction in a big way^[2] through the process of genetic pollution i. Genetic pollution is undesirable Gene flow into wild populations In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Genetic pollution is undesirable Gene flow into wild populations e. uncontrolled hybridization, introgression and genetic swamping which leads to homogenization or replacement of local genotypes as a result of either a numerical and/or fitness advantage of introduced plant or animal^[3]. Introgression, in Genetics (particularly plant genetics is the movement of a Gene ( Gene flow) from one species into the gene pool of another by backcrossing The genotype is the genetic constitution of a cell an organism or an individual (i Fitness (often denoted w in Population genetics models is a central concept in evolutionary theory. Nonnative species can bring about a form of extinction of native plants and animals by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones where the abundant ones can interbreed with them swamping the entire rarer gene pool creating hybrids thus driving the entire original purebred native stock to complete extinction. Attention has to be focused on the extent of this under appreciated problem that is not always apparent from morphological (outward appearance) observations alone. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism Some degree of gene flow may be a normal, evolutionarily constructive process, and all constellations of genes and genotypes cannot be preserved however, hybridization with or without introgression may, nevertheless, threaten a rare species' existence^[4][5]. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance The genotype is the genetic constitution of a cell an organism or an individual (i

Models of gene flow

Models of gene flow can be derived from population genetics, e. Population genetics is the study of the Allele frequency distribution and change under the influence of the four evolutionary forces Natural selection, Genetic g. Sewall Wright's neighborhood model, Wright's island model and the stepping stone model. Sewall Green Wright ( December 21, 1889 – March 3, 1988) was an American Geneticist

Gene flow mitigation

When cultivating genetically modified (GM) plants or livestock, it becomes necessary to prevent "genetic pollution" i. Genetic engineering, Recombinant DNA technology, genetic modification/manipulation (GM and gene splicing are terms that apply to the direct Livestock is the term used to refer (singularly or plurally to a Domesticated Animal intentionally reared in an agricultural setting to produce such as Food Genetic pollution is undesirable Gene flow into wild populations e. their genetic modification from reaching other conventionally hybridized or wild native plant and animal populations by using gene flow mitigation usually through unintentional cross pollination and crossbreeding. Pollination in angiosperms and Gymnosperms is the process that transfers pollen grains, which contain the male Gametes (sperm to where the female A crossbreed or crossbred usually refers to an animal with Purebred parents of two different breeds varieties or populations Reasons to limit gene flow may include biosafety or agricultural co-existence, in which GM and non-GM cropping systems work side by side. Biosafety: prevention of large-scale loss of Biological integrity, focusing both on Ecology and Human health In the context of agriculture and food and feed production co-existence means using cropping systems with and without Genetically modified organisms (GMOs in parallel

Scientists in several large research programmes are investigating methods of limiting gene flow in plants. Among these programmes are Transcontainer, which investigates methods for biocontainment, SIGMEA, which focuses on the biosafety of genetically modified plants, and Co-Extra, which studies the co-existence of GM and non-GM product chains. Biological containment (or biocontainment describes measures aimed at preventing Genetically modified organisms (GMOs and their Transgenes from spreading into the Co-Extra is an EU-funded research programme on ''co-ex''istence and ''tra''ceability of genetically modified crops and their edible derivatives

Generally, there are three approaches to gene flow mitigation: keeping the genetic modification out of the pollen, preventing the formation of pollen, and keeping the pollen inside the flower.

• The first approach requires transplastomic plants. In transplastomic plants, the modified DNA is not situated in the cell's nucleus but is present in plastids, which are cellular compartments outside the nucleus. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change An example for plastids are chloroplasts, in which photosynthesis occurs. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. In some plants, the pollen does not contain plastids and, consequently, any modification located in plastids cannot be transmitted by the pollen. Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of
• The second approach relies on male sterile plants. Male sterile plants are unable to produce functioning flowers and therefore cannot release viable pollen. Cytoplasmic male sterile plants are known to produce higher yields. Male sterility is defined as the failure of plants to produce functional Anthers Pollen, or male Gametes. Therefore, researchers are trying to introduce this trait to genetically modified crops.
• The third approach works by preventing the flowers from opening. This trait is called cleistogamy and occurs naturally in some plants. Cleistogamy or automatic self-pollination describes the trait of certain plants to propagate by using non-opening self-pollinating flowers Cleistogamous plants produce flowers which either open only partly or not at all. However, it remains unclear how reliable cleistogamy is for gene flow mitigation: a Co-Extra research project on rapeseed investigating the matter has published preliminary results which cast doubt on the attainment of a high degree of reliability.

See also

• Biological dispersal
• Genetic pollution
• Genetic erosion

External links

• Co-Extra research on gene flow mitigation
• Transcontainer research on biocontainment
• SIGMEA research on the biosafety of GMOs: http://sigmea.dyndns.org

References

• Su, H et al. (2003) "The Great Wall of China: a physical barrier to gene flow?. " Heredity, Volume 9 Pages 212-219

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