A person’s GENES are always presented in pairs, one gene in turn coming from the mother’s pair and the other of the father. Sometimes it happens that these inherited genes are abnormal (pathogenic variant), and it may even happen that both genes are. Normally these abnormal genes cannot perform their coding function.
In dominant genetic diseases it is only necessary to inherit an abnormal gene, either from the mother or the father, to suffer from the disease and this is because the function of the abnormal gene cannot be supplied by the other gene of the pair. In recessive genetic diseases, the two inherited genes must be abnormal to cause the disease since the function of an abnormal gene is replaced by the other non-abnormal.
People with only one defective gene in the pair are considered carriers and as we have already seen, in the case of genetic diseases recessive do not suffer from the disease. However, this person can transmit the defective gene to the offspring, who will again be a carrier, non-carrier, or diseased depending on whether the other inherited gene is normal or abnormal.