Point mutations are caused just by the replacement of single nucleotide with another. These mutations occur during the process of replication of DNA molecule. The cause of the mutation is some chemicals which affect the DNA molecule during replication. Single base substitutions take place in the sense that if one purine base is replaced with the other purine base i.e. A or G, then transition occurs but if one purine replaces one pyrimidine or the vice versa then that mutation is called as transversion. The mutation or defect in the gene by chemicals during the DNA replication then it is called as genetic disorder.

Point Mutations and causes of Cystic Fibrosis:-
Cystic fibrosis is a hereditary disease caused by the genetic disorder due to the changes in one gene. It is named as cystic fibrosis as it is caused due to the fibrous scar in the tissue. The tissue is developed in the pancreas which is the main region effected by cystic fibrosis. This disease occurs in the lungs, stomach and sweat glands of the body. During the disease, body's cells cannot properly take salt and water in and out. Due to this reason, thick mucous produces in the lungs which block the passages of the lungs and lungs do not function properly.

Causes:-
As already described, cystic fibrosis is a genetic disease that it passes from one generation to the next. Defect in the gene is the reason of occurrence of this disease. Genes are the parts of DNA molecule are present inside the nucleus. They are responsible for production and controlling the function of proteins. A gene called CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) is the cause of cystic fibrosis if defects start appearing in it. There are chances of occurrence of 500 defects in this gene but the defect which is present in most of the patients suffering from cystic fibrosis is called as delta-F508. Genes are just like the long strings of sentences. If in a sentence, change of one character takes place, the meaning of the whole sentence will be changed, similarly if changes occur in the single nucleotide of the long sequences of the genes due to chemical changes then the whole function of the genes will be changed and they will not be able to work properly.

CFTR protein is responsible for producing mucous which is composed of salts, sugars and water. The mucous helps in cleaning and protecting the passages of lungs and pancreas and makes the normal flow of salts and water in and out of the body cells. Chloride ions present in the mucous are set free from the cells with the help of CFTR protein. Due to its departure from the mucous cells, the mucous becomes thin because water also follows the same path. The function of CFTR protein is to keep the mucous thin so that it can clean all the passages of lungs and pancreas.

During the genetic disorder cystic fibrosis, CFTR protein does not function properly. It does not allow the chloride ions to move out of the mucous producing cells. Due to this reason, the mucous becomes thick and faces difficulty from passing through the passages of lungs and pancreas. Thus it feels difficult to perform its function of cleaning the passages properly due to its thickness. If the cystic fibrosis occurs in pancreas, then it does not allow the mucous to clean the passage, due to this the digestive enzymes feel difficult to move to the intestine and help in digesting the food.

This disease appears in the children if both the parents are carriers of cystic fibrosis. If one parent is carrier and one is normal then there are less chances of appearing the disease in children.

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