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The causes and consequences of variation

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Introduction

The causes and consequences of variation Variation is the differences that exist between members of the same species. It can be caused by environmental or genetic factors. Genetic variation tends to be permanent and stays within the population gene pool (unless it is erased via evolution) and can effect both the phenotype and the genotype of an organism. The environmental differences within or between species cannot be inherited by offspring and are only able to influence the phenotype of a species. Variation can either be continuous and discontinuous. Continuous variation is when there is a complete range of measurements between two extremes. An example of this type of variation can be seen in the height of humans, which ranges from the shortest to the tallest individual in a population. This is an example of polygenic inheritance and the pattern of variation reflects the fact that there are many different combinations of alleles possible for human height. Discontinuous variation is variation in which individuals fall into distinct categories is between one type and another, this type of variation is caused by major genes and is unaffected by the environment. An example of this type of variation if the ABO blood groups, a persons blood group doesn't change just because they don't have the right diet for example or get a tattoo. ...read more.

Middle

People infected by the disease tend to die young and are less likely to pass on their genes. This means that their genes will eventually be eliminated from the gene pool (in certain areas, for example Britain -where malaria is a very rare disease) however, in other areas that gene may be beneficial, as in this case, so its function in the gene pool is significant. This is an environmental cause of variation between a species (human) -the process of selection, described above. Gene flow can also causes variation, it is the exchange of genes between populations of a species. For example, the various populations of magpies found in different locations around Australia do not usually interbreed, and they have observably different phenotypes in different areas. However, if some magpies migrate between locations, and interbreed with the magpies in the new location, their genes have 'flowed' out of the original population and into the second population. This introduction of new genes into a population is often beneficial as it may supply the so-called hybrid vigour, which increases the survival potential of the next generation of individuals. Environmental differences can be very important when considering variations within a species. For example, some twins have an identical genetic make-up and it would expect that these be exact copies of each other throughout their lives if they grew in similar conditions but big differences in diet could make one twin much taller or heavier than the other. ...read more.

Conclusion

These gene-altered fish pose threats to wild fish, in rivers and oceans, and as well as to those who eat them. These threats are irreversible, once genetically engineered fish escape into open waters, they can never be recalled. This may cause variation in rare cases and even cause a new species to evolve. Many crops and vegetables are also genetically modified; certain desirable characteristics are emphasised a lot more in the genotype than in the natural form of the organisms. This type of variation can be disastrous on a species ability to evolve and adapt to new environments via evolution. To conclude variation has as many wide spread causes as it does consequences. Its importance on earth is immense and it is due to variation in species that the human has evolved. The true, literal source of variation has been shut up inside the genome of species for a long time. It consists of (in the case of the structural genes which code for proteins) an abundance of genetic material. Mutations damage those genes, which upsets balances and/or causes 'new' characteristics to appear. However, those characteristics were already contained within the organism. In other words, precision prevention and repair of mistake mutations are programmed into the genome, or designed if you will. As a result of the built-in designed, system of natural variation ...read more.

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