Polymorphisms or the genetic variations spring from mutation. There are many ways for genetic differences to happen. There is the mitosis, from which the variations occur during the somatic cell division. It could also occur in meiosis or during the process when the cycle of sperm and egg cells has to go through. When these variations occur, lots of consequences can happen. They can be passed along to the offspring, creating more changes over the years, or can result to an illness. At other times, the genetic variations do not bring any apparent effect.
Polymorphisms can be classified into different categories, but the most common are silent genetic variations, unstable genetic variation, and stable genetic variation.
In silent genetic variations, the mutations or alterations in a gene does not result in changes in the protein product of the gene. Thus, the silent genetic variation can rarely bring an illness.
In unstable genetic variations, however, the nucleotide sequence commits several repetitions by itself, hence, it is sometimes called the 'repeat' variation. If the repeat becomes constant and unchanging, this should not pose any threats to the individual. Nevertheless, if the repetition sequences increases largely, it becomes an 'expanded repeat' and can be a cause of many genetic illnesses. An example of a disease caused by an expanded repeat variation is the Huntington disease, a severe brain disorder characterized by hydrocephalus, dementia, and unusual movements.
On the other hand, the stable genetic variations are a consequence of particular alterations in single nucleotides. The said alterations are termed Single Nucleotide Polymorphisms or SNPs, and can involve the substitutions, deletions and insertions.
The substitutions refer to the incidence in which one single nucleotide is replaced by another, while deletions mean that a certain single nucleotide is lost, and finally, insertions are an indication that one or more nucleotides are inserted into a specific gene.
An incidence called 'missense mutation' occurs when the SNPs result in making a new amino acid. An example of such incidence is the Sickle Cell Anemia, in which one of the nucleotide has been substituted by another. In Sickle Cell Anemia, the polymorphism results in having a different amino acid to be added into a protein, which in turn, lead into a protein that does not function properly, and yet causes some cells not to carry oxygen but to form sickle shapes.
Other genetic variations happen when the whole gene is copied somewhere in an individual's genome. When such thing happens, the presence of extra copies of genes become apparent and creates additional protein product. This type of mutation can lead to Charcot-Marie-Tooth disease type 1.
There are also mutations happening in a specific portion of a gene that controls when the DNA is duplicated to RNA. A decreased in protein production may result if the timing of protein production is put off.
Finally, there is a genetic variation that results in a defective gene making a protein that acts to fix broken DNA in the human cells. Such variation can have many diseases as the consequences, and this includes a xeroderman pigmentosum, a type of skin disease; and colorectal cancer.
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