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Nucleic acids
- Ravi will need to contact his GP and arrange to have a cystic fibrosis carrier test. In this simple test Ravi will be asked to use a mouthwash to rinse his mouth out and the mouthwash will be collected and sent to the laboratory for analysis. The mouthwash will contain enough of Ravi’s cells for the laboratory to extract his DNA to test for the presence of the cystic fibrosis mutation.
- Our chromosomes come in pairs. That means that we have two copies of each. Cystic fibrosis is a recessive disorder. As a carrier Angela will have one copy of chromosome 7 with a cystic fibrosis mutation and one copy of chromosome 7 with the normal gene. The baby received one chromosome from each parent. Therefore there is a 50% chance the baby will receive either the chromosome with the normal gene or the mutated gene from Angela. If Ravi is not a carrier for the genetic disorder then the baby cannot inherit cystic fibrosis as it can only inherit a normal copy of the gene from Ravi. The baby can however be a carrier for the disorder, the same as Angela.
- If they were both cystic fibrosis gene mutation carriers, Ravi and Angela would each have a normal and a mutated version of the gene on chromosome 7. If the baby had received a chromosome with the mutated gene from both Ravi and Angela, the baby would have cystic fibrosis (a 1in 4 chance, 25%). If only one of them passed on a chromosome with the mutated gene the baby would be a carrier of cystic fibrosis (a 1 in 2 chance, 50%). If neither of them passed on the chromosome with the defective gene the baby would not have or carry cystic fibrosis (also a 1 in 4 chance, 25%).