Cystic Fibrosis
- Genes can affect the phenotype of an organism
- A gene codes for a single polypeptide
- The polypeptide can affect the phenotype, e.g. it could form part of an enzyme or a membrane transport protein
- Genetic disorders are often caused by a mutation in a gene that results in a differently-functioning or non-functioning protein that alters the phenotype of the individual
Cystic fibrosis
- Cystic fibrosis is a genetic disorder of cell membranes caused by a recessive allele of the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene located on chromosome 7
- This gene codes for the production of chloride ion channels required for secretion of sweat, mucus and digestive juices
- A mutation in the CFTR gene leads to production of non-functional chloride channels
- This reduces the movement of water by osmosis into the secretions
- The result is that the body produces large amounts of thick, sticky mucus in the air passages, the digestive tract and the reproductive system
- Because cystic fibrosis is determined by a recessive allele, this means
- People who are heterozygous won’t be affected by the disorder but are carriers
- People must be homozygous recessive in order to have the disorder
- If both parents are carriers the chance of them producing a child with cystic fibrosis is 1 in 4, or 25 %
- If only one of the parents is a carrier with the other parent being homozygous dominant, there is no chance of producing a child with cystic fibrosis, as the recessive allele will always be masked by the dominant allele
Cystic fibrosis is a genetic disorder caused by a recessive allele
The respiratory system
- Mucus in the respiratory system is a necessary part of keeping the lungs healthy
- It prevents infection by trapping microorganisms
- This mucus is moved out of the respiratory tract by cilia
- In people with cystic fibrosis, due to the faulty chloride ion channels, the cilia are unable to move as the mucus is so thick and sticky
- This means microorganisms are not efficiently removed from the lungs and lung infections occur more frequently
- Mucus builds up in the lungs and can block airways which limits gas exchange
- The surface area for gas exchange is reduced which can cause breathing difficulties
- Physiotherapy can support people with cystic fibrosis to loosen the mucus in the airways and improve gas exchange
The digestive system
- Thick mucus in the digestive system can cause issues because
- The tube to the pancreas can become blocked, preventing digestive enzymes from entering the small intestine
- Digestion of some food may be reduced and therefore key nutrients may not be made available for absorption
- The mucus can cause cysts to grow in the pancreas which inhibit the production of enzymes, further reducing digestion of key nutrients
- The lining of the intestines is also coated in thick mucus, inhibiting the absorption of nutrients into the blood
- The tube to the pancreas can become blocked, preventing digestive enzymes from entering the small intestine
The reproductive system
- Mucus is normally secreted in the reproductive system to prevent infection and regulate the progress of sperm through the reproductive tract after sexual intercourse
- The mucus in people with cystic fibrosis can cause issues in both men and women
- In men the tubes of the testes can become blocked, preventing sperm from reaching the penis
- In women thickened cervical mucus can prevent sperm reaching the oviduct to fertilise an egg