Notes : 2.12 + 2.14 - Inheritance Flashcards
What is a mutation?
A mutation is a change to the base sequence of DNA occurring when the cell makes errors during DNA replication.
Define substitution.
Substitution - one base is replaced for another e.g. TGCCTA becomes TGACTA. It results either in a change to a single amino acid, or the amino acid might stay the same because more than one codon can code for the same amino acid (the genetic code is degenerate).
Define insertion.
Insertion - one or more bases is added e.g. TGCCTA becomes TGCCCTA. This type of mutation will change the codon (and perhaps the amino acid) and all following codons (this is called a frameshift).
Define deletion.
Deletion - one or more bases is removed e.g. TGCCTA becomes TGCTA. Deletion mutations will change the codon at the point of mutation and all following codons, resulting in a frameshift.
Define inversion.
Inversion - a sequence of bases is reversed e.g. TGCCTA becomes TGCATC. It will result in a change to a single amino acid.
What is cystic fibrosis ?
Cystic fibrosis is a genetic disorder that primarily affects the lungs and digestive system. It is caused by mutations in the CFTR gene. This gene is responsible for producing a protein that acts as a chloride channel in our cells. The **faulty chloride channels **in the cells cause a disruption in the flow of chloride ions. This disruption affects the balance of fluids in the body, including the mucus.
Normally, the chloride ions help attract water molecules which helps to maintain the proper hydration of mucus, keeping it thin and slippery. However, in cystic fibrosis, the lack of functional chloride channels leads to a decrease in chloride ions a decrease in water molecules in the mucus and an increase in sodium ions in the mucus. This imbalance causes the mucus to become thick, sticky, and harder to move. As a result, it can clog up the airways and make it difficult to breathe.
How is the respiratory system effected in people with cystic fibrosis ?
Respiratory system
- Build up of mucus in the lungs traps bacteria this increases the risk of infection.
- Build up of mucus in the airways reducing the surface area of alveoli available for gas exchange**making it harder to breathe. **
People with cystic fibrosis can be given antibiotics to kill the bacteria inside the mucus lining their airways. They can also have physiotherapy to help to dislodge the mucus and facilitate gas exchange.
How does cystic fibrosis affect the reproductive system ?
Reproductive system
- Cervical mucus prevents the sperm from reaching and fertilising the egg, this results in reduced fertility.
- In men, the sperm duct is blocked with mucus, meaning that the sperm produced can not leave the testes.
What is meant by the term gene ?
A sequence of nucleotides in DNA that codes for a polypeptide.
What is genetic screening.
A medical test that can be used to check whether an individual is a carrier of a recessive allele which can causes diseases, or to check for an unborn foetuses for genetic abnormalities.
What is prenatal testing
Testing the DNA of an unborn fetus whilsts its still growing in the mother’s womb.
Why would a mother under go prenatal testing.
If she thinks that the baby is at risk of a particular genetic disorder.
What are the ethical issues associated with DNA testing.
The results are not 100% accurate - a false positive means unnecessary stress and may lead to a couple choosing not to raise children whereas a false negative may mean that the mother gives birth to a child with cystic fibrosis without being emotionally or financially prepare.
- The DNA test may discover other DNA abnormalities, such as a mutation in a gene which leads to breast cancer, which can cause further stress.
- Life insurance companies or employers may use the results to discriminate against people with certain genetic disorders.
What is PGD ?
- A technique used during IVF to test for genetic abnormalities before implanted into the uterus.
