ALBINISM (Latin albus — white; synonym leucism) — inborn lack of normal pigmentation.
And. develops as a result of decrease of the activity of the enzyme of a tyrosinase normal turning tyrosine of pigment cells in melanin (see). The last also causes normal pigmentation of an individual. Reason partial And. there can be also a disturbance or delay of migration of melanoblasts to the place of their final localization or death of stem pigment cells at early stages of an embryogenesis.
Distinguish full and partial A. Polny A. it is characterized by lack of pigmentation; such individuals are called by albinos, or by leykopatam. Leather of albinos is very sensitive to sunshine, even small doses of solar radiation can cause in them heavy burns.
Eyes at albinos — rose-red owing to raying of blood vessels of an iris of the eye. Due to the lack of a pigment in photoreceptors of a retina their excess disintegration of a rhodopsin of rhodopsin is noted. Therefore albinos badly see in the afternoon (a day blindness), the photophobia (photophobia) is inherent in them. Partial And. it is characterized by lack of a pigment only in separate parts of a body. Degree and a form of a depigmentation at the same time widely vary. E.g., at one of forms A. — an acromelanosis — at some animals skin and hair white, eyes red, and the nose and tips of a tail, ears and paws are pigmented. Or, e.g., skin and hair (or feathers) are depigmented, and eyes black. Example partial And. the person has a white lock of hair, white spots on skin.
It is established that full And. belongs to retsessivno to the inherited pathology, i.e. And. it is shown only at individuals, homozygous on this gene (see. Mendel laws ). The carried-out calculations show that if albinos meet in population frequency of 1 on 20000, then about one individual from 70 in this population is the heterozygous carrier of a recessive gene. Frequency of the birth of children albinos in case of marriage of two albinos — 100%, in case of marriage of an albino and the carrier of a recessive gene And. in a heterozygous state — 50%.
The probability of the birth of an albino in case of marriage of two carriers of this allele in a heterozygous state makes 25%.
T. D. Gladkova, B. V. Konyukhov.