Causes of Variation
Variation is a result that leads to a difference or deviation (for example, structure, form, function) from the recognised norm or standard. It is a modification in structure, form or function in an organism, deviating from other organisms of the same species or group. There are two types of variation: interspecific variation and intraspecific variation. Interspecific variation is when one species differs from another like mammals differ from fish. These differences are explained through differing ancestries explained by the difference of genetics perhaps due to natural selection. However, intraspecific variation is when members of the same species differ from each other like how there are many different types of cats. This can be mainly explained through mutations.
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Variation is the result of two main factors: genetic differences and environmental influences. In most cases it is a combination of both factors. Additionally, in asexual reproduction, variety can only occur through mutations whereas off springs that have been produced sexually the variety will be more apparent due to the probabilities being higher due to more factors contributing to the cause of variation such as meiosis and fusion of gametes, as well as mutation.
Genetic differences are due to the different genes that each individual organism possesses. The differences occur arise in living organisms and change from generation to generation. Genetic variation arises as a result of mutations, meiosis and fusion of gametes. Mutations are changes in DNA that result in the offspring containing different characteristics by the changing of quantity or structure of the DNA.
The end result of the process of altering the DNA structure is a different amino acid sequence that leads to a formation of a different polypeptide, and hence a different protein, or no protein being produced at all. So, as proteins are responsible for the characteristics of an organism, it follows that changes to DNA are likely to alter an organisms characteristics. These sudden changes to genes and chromosomes may, or may not be passed onto the next generation.
Genetic differences are also explained through meiosis. Meiosis is the process in which four daughter nuclei’s are produced, each with half the number of chromosomes as the parent cell. It allows the offspring to adapt and survive in the changing world by allowing genetic variation through the independent segregation of homologous chromosomes due to the homologous pairs of chromosomes arranging in a new, random order. Also, the recombination of homologous chromosomes crossing over causes variation. Overall, meiosis mixes up the genetic material before it is passed into the gametes, all of which are therefore different.
Lastly, genetic differences are also explained through the fusion of gametes. In sexual reproduction the offspring inherit some characteristics of each parents and are therefore different from both of them. Which gamete fuses with at fertilisation is a completely random process that emphasises the variation occurring in the offspring.
On the other hand, environmental influences also have a massive input in variation. The environment influences the way in which the genes are expressed. The genes allow certain things to happen whereas the environment determines where each characteristic is utilised. For example, a plant may contain genes that allow it to grow tall however, it is the environment that allow this stage to progress so if the seed germinates for example, the plant will not be able to utilise it’s beneficial characteristics to the highest extent. Examples of environmental influences are: climatic conditions (such as rainfall, temperature and sunlight), soil conditions, food availability and pH.
Overall, variation is caused due to a combination of environmental influences and genetic differences. However, it is hard to distinguish between the effects of environmental and genetic so is difficult to draw conclusions about the causes of variation.