Lyonización desfavorable: A propósito de una familia con retinosis pigmentaria

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