Hybrid Diseases

Hybrid Diseases. Like any other trait, pathological traits can be passed on to offspring through hybridization, and their further development, that is, their manifestation, will depend on the general laws of Mendel, specifically whether they have a dominant or recessive character. In the first case, the disease in a homozygous carrier of the pathological trait will manifest in the first generation according to the scheme: DD x RR = DR. In a heterozygous carrier, however, half of the offspring has a chance of being healthy, while the other half will again be diseased (DR x RR = DR + RR). When both parents are heterozygous, some offspring will be phenotypically and genotypically diseased, others will also be diseased but will carry the factor for healthy condition in a latent form, while the third group will be healthy (DR + DR = DD + 2DR + RR), with the latter group, when crossed with similarly healthy individuals, continuing to produce entirely healthy offspring. When the pathological trait is recessive, crossing a diseased individual with a homozygous healthy one will produce phenotypically healthy offspring; when the healthy parent is heterozygous (DR), half of the offspring will be phenotypically healthy, while the other half will be both phenotypically and genotypically diseased (RR). When both parents are heterozygous for normal traits, some offspring will be unquestionably healthy, others will be healthy in appearance but not genotypically, while the third group will definitely be diseased (RR). Thus, from two heterozygous diseased parents, a group of healthy offspring can segregate, while from two heterozygous healthy parents, a group of diseased offspring can segregate. This is how pathological traits are distributed in offspring in monohybrid crosses, while in dihybrid and polyhybrid crosses, the relationships, though essentially the same, become more complex. For example, in the case of a homozygous recessive disease transmitted according to a dihybrid segregation scheme, only an individual combining both recessive genes will definitely be diseased; while with only one disease gene present, the subject remains on the borderline between normal and pathological. Incidentally, this type of regularity is assumed by the school of Hoffmann as the basis for the inheritance of schizophrenia (so-called schizoidism with the presence of one disease gene).