Genetic compatibility test It is mainly used in oocyte reception cycles. If until now it was customary to choose among potential donors due to phenotype similarities with the recipient woman, now it is also possible to rule out those egg donors who would entail an increased risk of transmitting genetic diseases. However, it is also available for those couples who want to know more about their genetic compatibility. In the event that both members of the couple turn out to be carriers of alterations for the same gene, there are various options to ensure the birth of healthy children, such as carrying out an in vitro fertilisation cycle with pre-implantation genetic diagnosis to avoid the transfer of affected embryos or replacing one of the gametes with gametes from a donor who is genetically compatible for that particular disease. We all have two copies of each gene, one inherited from the father and one from the mother. In the case of monogenic recessive diseases, both copies of the gene must be altered for the disease to manifest itself. Carriers are those people with alterations in only one of the two copies: they do not manifest the disease but they have the risk of transmitting it. When we reproduce, our child inherits two copies of each gene, one from each parent. In the case that both parents are carriers for the same monogenic disease, the child will have a 25% probability of not showing alterations in any of the two copies of that gene, 50% of being a carrier without showing symptoms and 25% of suffering from that disease.