Albinism

ALBINISM (from Latin albus - white), the absence of pigments in the coverings of animals that are normally pigmented. A distinction is made between complete and partial albinism. In the case of complete albinism, pigment is absent not only in the hairs, even in the downy hairs and skin, but also in the eye coverings, which are normally pigmented. The skin and hair of albinos, due to the absence of pigments, are white, and the eyes are red, as the blood of the choroid of the eye is visible. Albinos see poorly during the day, as light, which is normally absorbed by pigment in the eye, abundantly penetrates into the chamber of the eye in albinos. Albinos see better in twilight. An example of complete albinism can be white, red-eyed rats, mice, rabbits. As a rare phenomenon, complete albinos are known among wolves, foxes, saiga antelopes and many other animals. Cases of complete albinism have also been described in humans. According to calculations made for Norway, there is one complete (red-eyed) albino per 200,000 children. Partial albinism differs from complete albinism in that pigments disappear not throughout the animal's covering, but only in certain places. The degree of discoloration of the animal in partial albinism can vary widely. The coverings are either discolored throughout the body, and pigments are preserved only in the eye, or the coverings (hair, feathers, skin) are discolored only in spots (patches). Cases of partial albinism are known in crows, sparrows, goldfinches and many other birds, as well as in many mammals and including humans. In Negroes, partial albinism can manifest as the appearance of white spots on dark skin; depigmentation can sometimes cover such a large area that dark spots are only small islands. Sometimes albinism in a Negro manifests in the form of blond hair and blue eyes with dark skin. Among Europeans, partial albinism manifests in the form of discolored tufts of hair on the head. For Germany and Scotland, it has been established that there is one partial albino per approximately 20-25 thousand people. The conditions for the occurrence of partial albinism are not entirely clear. Very often albinism is associated with general weakness of the organism. It is well known that the white (albinotic) variety of axolotls is less viable than the normal, black race. Livestock breeders know that partial albinism, in the form of depigmentation of the wing feathers and feathers of other parts of the body, often accompanies the weakening and deterioration of purebred chickens. Along with natural albinism, there are known cases of obtaining partial albinism under laboratory conditions. Thus, for example, when feeding the thyroid gland or its preparations to pigmented chickens, pigeons and other birds, as well as mammals, new feathers and hair grow partially or completely depigmented; thus, pied individuals arise. One can assume that some cases of partial albinism observed in nature are associated with hyperfunction of the thyroid gland. Partial albinism can have different origins, but it is not yet possible to accurately classify albinism according to the mechanics of its formation. Along with complete and partial albinism of the type described above, a very characteristic manifestation of incomplete albinism is known, in which a white, red-eyed animal (rabbits, guinea pigs) retains pigment on the ears, nose, tail and tips of the paws. An illustration of such a coloration (which received the name of acromelanin) can be the so-called Himalayan, or ermine rabbits and guinea pigs. There are similar types, Siamese cats. Ermine rabbits are born pure white, and only at the end of the first month, the hairs on the ears, nose, tail and paws begin to become pigmented. At the present time, it has been clarified that, in the case of development at high t°, white hairs grow not only all over the body, but also on the ears, nose, etc. In the case of development of a rabbit at low t°, pigmented hairs grow on any part of the body where white hairs normally grow. In other words, in ermine rabbits, the development of pigments is closely related to t°, and in one place of the skin coverings, pigment develops at one t°, in another - at another t° of the external environment. Both complete albinism (in rabbits, rats, etc.) and partial albinism of the ermine rabbit type represent hereditarily stable traits, and when crossing two pure albino homozygous individuals (see Mendelism), all their offspring retain the albino type. When crossing albinos with a pigmented individual, in the first generation, as a rule, in most vertebrates, pigmented offspring is born, i.e., the trait of albinism is recessive in relation to the trait of pigmentation. But in some white breeds of chickens, sheep, etc., the white coloration (incomplete albinism) is dominant. In some cases, from two albinos, pigmented offspring can also be obtained, the origin of which will become clear if one becomes acquainted with the origin of pigment in the coverings of the organism. Pigment is obtained as a result of the interaction of two agents: a colorless chromogen and an enzyme of the tyrosinase type. If one of these agents is present in the organism, then the coloration does not manifest. But if one crosses an albino with a chromogen and an albino that has tyrosinase, then when the germ cells merge in the offspring of these albinos, individuals with chromogen and tyrosinase at the same time can be obtained. These will be the pigmented ones.