A mutation in the HBB gene can cause the formation of haemoglobin S (HbS) which leads to sickle cell disease. So, in this case the mutation is harmful. On the other hand, people who are heterozygous for the mutant allele are resistant to malaria and in this case mutation is beneficial.
A mutation in EYC3 gene is neutral, because the change of eye color is either beneficial or harmful.
A mutation in CFTR gene is harmful, because malformed CFTR protein can't perform its key function in the cell. As a result, the balance of Cl and fluids is disrupted, causing mucus in various organs to become thick and sticky.
A mutation in LRP5 causes high bone mass and consequently, many bone density related diseases. So, this mutation is harmful.
