Resumo

RANGEL FLEITES, Rubén; TABOADA LUGO, Noel; LIMA LEON, Carlos  e  MEMBRIDES PEREZ, Gladys. Unfavorable lyonization: Apropos of a family with retinitis pigmentosa. Rev Cubana Oftalmol [online]. 2005, vol.18, n.1, pp. 0-0. ISSN 1561-3070.

During many years the expression of the genes linked to x chromosome has been a mistery for geneticists. Men have only one copy of each gene linked to x chromosome, whereas women have two. The amount of product formed by only one allele in males, or by a couple of alleles in females was equivalent. Finally, this was explained with the formulation of the principle of inactivation of x chromosome that has 3 important consequences: dose compensation, mosaicism and variability of expression in heterocygotes. A manifested heterocygote, in which the deleteroous allele is located in the active x chromosome and the normal allele in the inactive x chromosome, in all or most part of the cells, is an example of what is known as unfavorable lyonization. This phenomenon has been described in many disorders linked to x chromosome, including blindness to color, hemophylia A or B, Duchenne's muscular distrophy and various ocular disorders linked to x chromosome. A clinical genetical study of a family with diagnosis of typical retinitis pigmentosa of recessive heredity linked to x chromosome, where the phenomenon of unfavorable lyonization is present, was conducted

Palavras-chave : Mosaicism; x chromosome; retinitis pigmentosa [genetics].

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