Humans have two copies of each gene, one inherited from each parent. This means for most genes, you have a pair—one from your mother and one from your father. When it comes to recessive genetic diseases, if one gene in the pair is mutated but the other is normal, the person doesn’t usually show symptoms but can pass the mutated gene to their children. If both genes are mutated, the disease typically manifests because there’s no normal gene to compensate.
Parents (or donors) can be screened to identify mutations and assess the risk of passing genetic diseases to their children. PGT-M can be used to identify embryos that are affected or are carriers for the genetic disorder.