DNA replicates itself in a complex process during mitosis and meiosis. However, when the DNA replication goes wrong and the gene changes, it produces an allele. This is why an allele is defined as the different forms of genes. This change in gene is called a genetic mutation.
Mutation also occurs in chromosomes. The change in the shape or the amount of chromosomes present is called chromosome mutation. This can cause abnormality.
Genetic Mutation is a random event and is not caused by a medium or a disease.If it occurs in a specific cell of the body like the muscle cells or any other kind, It can be harmful to a cell. If it is harmful the cell soon dies and the mutation does not effect the body of an organism. However, If the genetic mutation is not harmful enough, the cell will survive and will eventually divide, producing the cells with the same kind of mutation. This kind of mutation is called somatic mutation. This can also cause cancer.
Albinism is a good example of genetic mutation. Every organism has a pigment in their skin called melanin. It is formed by an enzyme reaction formed from the alleles. In Albinism, due to the faulty gene, the enzyme cannot be produced which is why melanin might not be present. This causes the lack of pigmentation or color in skin, hair and eyes.
Lack of color in skin is very harmful. In small animals which falls prey to the predators, they lack the normal color of their skin and do not have the camouflage ability and fall prey to predators. In humans, albinism in skin is very harmful. It makes the patient vulnerable to the sun’s rays and will very well develop skin cancer. Patients with albinism do not live long enough to pass these genes on to the next generation.
Sickle Cell Anemia
Sickle cell anemia is another example of genetic mutation. It is a disease commonly found in sub-Saharan Areas of Africa and other places around the equator. The sickle cell anemia is a genetic mutation of the gene which has the genetic information for forming the protein hemoglobin. Once the mutation occurs the hemoglobin is formed in abnormal amounts. This stimulates the red blood cells to turn into sickle shaped. In this state the red blood cells become more fragile and carry less oxygen. The sickle shaped red blood cells are also destroyed by the spleen faster than the normal red blood cells. This causes anemia. Anemia is a disease in which the person is lacking a huge amount of red blood cells.
The allele of the normal person is written as Hb^A while those who have the mutated allele is Hb^S. A heterozygous human would be a carrier of the disease but does not show its symptoms in most humans. Those people who are homozygous will show symptoms of the disease. Thus the chart is as follows:
Hb^A Hb^A Hb^A Hb^S Hb^S Hb^S
Normal Carrier of the disease Sickle Cell Anemia
No symptoms Symptoms are rarely shown Symptoms are visible
It is quite advantageous to heterozygous human with the disease because this gives them the protection against malaria. When the pathogen is released into the blood, the sickle shaped red blood cells burst because they are so fragile and so the pathogen cannot absorb oxygen from the hemoglobin of these cells for respiration. These people can reproduce and can produce offspring which are invulnerable against malaria. This also shows the example of natural selection.