Humans transmit the genetic code to the next generation through DNA, containing 23 pairs of chromosomes. The seventh chromosome contains the defective gene that causes cystic fibrosis. There are over ten million Americans who this defective gene without having the disease. When both parents are carriers there is a 25% chance that the child will have a recessive gene; that is, the child has two copies of the defective gene from both parents. This gene signals the epithelial cells to produce cystic fibrosis trans-membrane conductance regulator (cystic fibrosisTR). It is a bad protein found in the digestive system, skin and reproductive system of cystic fibrosis patients.

When the cystic fibrosisTR is not normal, the regulation of salt through the membranes becomes defective. This results in the secretions of the lining such as mucus, digestive juices and sweat, becoming thick and sticky.

The respiratory system secretes thin and slippery mucus to clear away the foreign bodies and microorganisms that invade the system. In cystic fibrosis patients this mucus, thick and sticky, not only fails to clean the system but also blocks the lungs and airways and creates a life-threatening problem with the respiratory system. As the microorganisms are not cleared there are serious infections, like bronchitis, pneumonia and influenza. So a cystic fibrosis patient has to take care of his respiratory system constantly, with bronchodilators, electrical clappers and electrical inflatable vest vibrators. Newer antibiotics control the infections to a good extent.

In the digestive system the ducts between the pancreas and intestine and between the liver and intestine are blocked. Due to the shortage of enzymes and bile, the cystic fibrosis patient is unable to digest fats and proteins. He becomes malnourished, underweight and weak. Enzyme and vitamin supplements take care of the problem to an extent. In the reproductive system the duct between the testes and prostate get blocked, and so a majority of cystic fibrosis patients are sterile.