title: X chromosome constitution and the human female phenotype.
abstract: The correlations of abnormal X chromosome constitutions and the resulting phenotypes in the human female are reviewed. The following hypotheses put forward to explain these correlations are discussed in detail: (1) The damage is done before X inactivation; (2) An effect is exerted between reactivation of the X chromosome(s) and meiosis in oocytes; (3) A recessive gene(s) in hemizygous condition might be expressed in the cases in which the same X is active in all cells; (4) A change in the number of presumed active regions on the inactive X chromosomes might have an effect; (5) A position effect, in that the region Xq13-q27 has to be intact in both X chromosomes to allow normal development, may be responsible; (6) An effect during the period when cells with different inactivation patterns compete is a probability; (7) The original X inactivation may be neither regular nor random. The conclusion reached is that the phenotypic effects of a specific X chromosome aberration may be simultaneously exerted through different pathways (Tables 1 and 2). Hypotheses (2), (4), (5), and (6) are considered probable. Hypothesis (3) has been discarded, and there is very little evidence for hypotheses (1) and (7).
mesh_terms: D000293:Adolescent; D000568:Amenorrhea / Q000235:genetics; D000818:Animals; D001724:Birth Weight; D002648:Child; D002869:Chromosome Aberrations; D002872:Chromosome Deletion; D002901:Chromosomes, Human, 13-15; D002905:Chromosomes, Human, 4-5; D002906:Chromosomes, Human, 6-12 and X; D005260:Female; D005808:Genes, Recessive; D006579:Heterozygote; D006801:Humans; D051379:Mice; D010641:Phenotype; D051381:Rats; D012641:Selection, Genetic; D012728:Sex Chromatin; D012730:Sex Chromosomes; D014178:Translocation, Genetic; D014314:Trisomy; D014424:Turner Syndrome / Q000235:genetics; D014960:X Chromosome