Approximately one in every 25 Canadians is a carrier of the malformed CFTR gene responsible for CF. All genes come in pairs. A carrier has one good copy and one bad copy of the CFTR gene and consequently does not have cystic fibrosis, and can never get the disease.  In most cases, they are not even aware that they are carriers, because they do not have cystic fibrosis, or any of its symptoms.

When two people who carry one faulty copy of the CFTR gene have a child, there is:

• a 25% chance that the child will be born with cystic fibrosis; (2 faulty copies of the CFTR gene inherited)
• a 50% chance that the child will not have CF, but will be a carrier; ( 1 faulty/1 good  CFTR gene inherited)
  
• a 25% chance that the child will not have CF, and will not be a carrier. (no faulty CFTR genes inherited)

With each pregnancy, the risks are exactly the same. Two carrier parents may have several children with CF or none at all.