X chromosome

About: X chromosome is a research topic. Over the lifetime, 9862 publications have been published within this topic receiving 407354 citations. The topic is also known as: GO:0000805 & chrX.

Locus on human X chromosome for dihydrotestosterone receptor and androgen insensitivity.

Abstract: We have studied androgen binding characteristics of cells for androgen insensitivity from an obligate heterozygote, who is the mother of three male pseudohermaphrodites with dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one) receptor deficiency. Specific dihydrotestosterone binding by skin fibroblasts from her wrist and pubis is within the normal range and indicates that androgen insensitivity is X-linked in man and is therefore homologous to the tfm locus in the mouse. A significant population of clones from the heterozygote has deficient receptor activity, and this finding is compatible with inactivation of one X-linked allele at this locus. Our results indicate the presence of a gene on the human X chromosome that is essential for normal male sexual differentiation and provide further evidence for homology between X chromosomes of all mammals.

Xp deletions associated with autism in three females.

Abstract: We report eight females with small deletions of the short arm of the X chromosome, three of whom showed features of autism. Our results suggest that there may be a critical region for autism in females with Xp deletions between the pseudoautosomal boundary and DXS7103. We hypothesise that this effect might be due either to the loss of function of a specific gene within the deleted region or to functional nullisomy resulting from X inactivation of the normal X chromosome.

A Cis-Acting Locus That Promotes Crossing over between X Chromosomes in Caenorhabditis Elegans

Abstract: This study reports the characterization of a cis-acting locus on the Caenorhabditis elegans X chromosome that is crucial for promoting normal levels of crossing over specifically between the X homologs and for ensuring their proper disjunction at meiosis I. The function of this locus is disrupted by the mutation me8, which maps to the extreme left end of the X chromosome within the region previously implicated by studies of X; A translocations and X duplications to contain a meiotic pairing site. Hermaphrodites homozygous for a deletion of the locus (Df/Df) or heterozygous for a deletion and the me8 mutation (me8/Df) exhibit extremely high level of X chromosome nondisjunction at the reductional division; this is correlated with a sharp decrease in crossing over between the X homologs as evidenced both by reductions in genetic map distances and by the presence of achiasmate chromosomes in cytological preparations of oocyte nuclei. Duplications of the wild-type region that are unlinked to the X chromosome cannot complement the recombination and disjunction defects in trans, indicating that this region must be present in cis to the X chromosome to ensure normal levels of crossing over and proper homolog disjunction. me8 homozygotes exhibit an altered distribution of crossovers along the X chromosome that suggests a defect in processivity along the X chromosome of an event that initiates at the chromosome end. Models are discussed in which the cis-acting locus deleted by the Dfs functions as a meiotic pairing center that recruits trans-acting factors onto the chromosomes to nucleate assembly of a crossover-competent complex between the X homologs. This pairing center might function in the process of homolog recognition, or in the initiation of homologous synapsis.