Gene Flow: Causes and Barriers
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Published: Tue, 05 Jun 2018
Variation of inherited traits in the section of individual organisms over a period of time is referred as evolution. The major renowned sources of variation are gene flow, genetic recombination and mutation. Gene flow that is also acknowledged as gene migrations is the genetic allele’s exchange within populations by migration of gametes, spores and individuals of the same species. This is common in species through crossbreeding, migration and cross pollination which yield hybrid organisms. Movement of genes is often carried out by human being and wind. When people move from one town or country to another and carry with them plants to experiment if they can grow in their new location gene variation commence. Differences in gene flow across populations depends on the type of organism, populations of inactive organisms tends to be more isolated from each other than population of actively moving organisms. This paper will examine gene flow as an aspect of evolution biology and provide a deeper understanding of its benefits to organisms.
Mobility in gene flow
One of the principal factors contributing the flow of genes between different populations is their movement habit. Plant population compared to animal population appears to be sedentary, hence, animals have high rate of experiencing gene flow. Migration and emigration of populations can reduce genetic differences within that particular group (Beurton, Peter, Raphael Falk et al 224). Through emigration, genes are carried away by the ongoing individuals to a new destination, whilst migration brings on board new genes to an existing gene pool. These processes are activated by perpetual diffusion and mixing of genes of a sexual population.
Barriers to Gene Flow
Human growth and advancement in technological world has not been without its cons to gene flow. This is a major obstacle to gene flow, especially in its many artificial and permanent development of the landscape. A structure like the Great Wall of China has hinder movement of many organisms and relocation of alleles of genes of indigenous plants population (Lewin 95). Another behavior that prohibits gene flow is the fencing of a game park where insider animals are restricted from meeting others from another park. Vast human progress and occupation can wipe out or partition ecosystems into a desert or secluded islands resulting to lessening genetic variation of the populations imprisoned there. In the efforts to facilitate gene flow scientists are increasingly crafting new ways to connect to these isolated species as away of maintaining viable genetic variation. The other distinguished barriers are the natural barriers that halt or slow the rate of migration of genes among populations. These are oceans, impassable mountains, hills and large and wide deserts that exhibit great challenges for animals’ movement. This hindrances leads to loss of genes in a population as fertile population are barred from meeting the weak or other strong ones (Beurton et al 124). These barriers in human population have created suspicion and tension among races to an extent of tribal animosity.
Conducted studies reveal that sex chromosomes (X and Z chromosomes) are affiliated to reproduction and sex genes (Lewin 88). These genes are a factor in the progression of post zygotic isolation especially in hybrid sterility. It has been noted empirically that strengthening of zygotic isolation does occur in certain conditions. Recombination between alleles is a significant factor that has been identified to be opposing reinforcement. Connections between genes that affect mating and those that affect hybrid fitness plus sex chromosomes have the likelihood of boosting the process of hybridizing species. These ideas fall short of extrapolating whether essential forms of non-adaptive effect of divergence with no gene flow are stagnant or they increase. As a result of this we discover that there exists co evolution of zygotic barriers to the flow of genes.
Gene flow in action
The lives of species is involves a lot of movements in search of satisfaction and fulfilling hierarchy of needs. Thus, migration has become a significant force of restructuring genetic variation. In the contemporary globalization characterized by wide dispersions of humans in search green pastures and mates gene exchange is take place fast. There are now inter-racial marriages aiding much generating patterns of hereditary variations. Migration can occur to a mass of people due war or search of resources and food or to an individual as a result of displacement or personal drive to explore. Large scale migration of people leads to accumulation of mutations and as a result population diverges as there is genetic drift. Individual movements in a small geographical area enhance genetic variation between populations. These migration behaviors have distinctive effects on population structure with each having its methodological challenges.
Gene flow accelerated by intermarriage between national or state communities occurs frequently within a short time period. It remains a challenge to determine temporal control and spatial control of historical human migration. Geographical sampling is a costly exercise, hence, to determine geographic scope of a specific event advanced genotyping technologies are used as they are economical. Determining temporal control which is when gene flow has occurred is even more challenging; DNA studies are examined to come up with resolution pertaining human mobility. New methods are underway to provide conclusive sequential bounds on flow of human genes using genetic data that will be analyzed to show human gene flow. To discover historical movements’ researchers use genetic markers like mitochondrial DNA and the Y chromosome as they are highly thought to be mainly instructive genetic markers. To study human history using these markers one has to understand that Y chromosome is passed from a father to sons while mitochondrial DNA is passed only from mother to off springs. This distinctive mode of transmission makes it easier to study human descent.
Due to high rate of random genetic drift in these systems Y chromosome and Mitochondrion DNA have been found to have uncertainty. Their records show biasness towards the sex-specific migration of women and men as they are small loci representing large region of human genetic variations (Slarkin 327). Nowadays, multiple markers can be screened across human genome due to rapid progress in use of genotype technologies. Hence, to determine if two populations have similar genetic variations has become simple. However, it requires advanced modeling and inferential statistics to enumerate and establish the amount of gene flow between them.
Gene flow from Neanderthals have made scientist to meditate and compare entire genomes. Complete genome sequence of Neanderthal has been sequenced by some scientist. Previously only mitochondria DNA were accessible from Neanderthal as they occur in numerous copies per cell which make it difficult to mine DNA from primeval remains (Barton & Bengtsson 360). In this conducted study there was no trace of gene flow between Neanderthal and human being albeit this research was not conclusive as Mitochondrion DNA could have been mislaid through genetic drift. A complete combination of genome sequence from three Neanderthal creatures has been led by Green and colleagues through use of advanced new technology of sequencing. In contrast to mitochondrion DNA there are data sets that show existence of gene flow from Neanderthal to modern human being. It has been identified that non-African descendant have at least 13 genetic regions that originate from Neanderthal siblings. Since these regions are not present in Africans descent, this is thus a sign to show that gene flow had occurred from Neanderthal to modern people as it is assumed some ancestors had left Africa around 50,000 years to look for other destination in the rest of the world (Servedio & Kirkpatrick 766).
An increase or decrease of a population affects gene pool frequencies as gene flow will have high chance to take place in a densely populated area while there will be minimal changes in a sparsely populated area. For example if all black people were to leave America, the next generation of humans would probably have few or no blacks. This study has revealed that gene flow can occur without migration especially in circumstances where people pays a visit to particular place and mate with natives even though they will eventually go back to their place. In this case, genes are transferred across those populations and the resulting generation is hybridized.
Gene flow occurs between species when segment of DNA are carried by viruses in their routine invasion of cells of plants and animals. Although this mechanism of transfer is seldom, there exist documented evidence for some species of microorganisms, mammals, reptiles and insects. Human beings have not been left behind in this process; there is a high probability that 40-50% of DNA sequencing might have been carried out by viruses (Slarkin 420).
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