Chromosome X News and Research

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The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million base pairs (the building blocks of DNA) and represents approximately 5 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in somatic cells (cells other than egg and sperm cells). This phenomenon is called X-inactivation or Lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Some genes on the X chromosome escape X-inactivation. These genes are located at the tip of the short (p) arm of the X chromosome in an area known as the pseudoautosomal region. Although many genes are unique to the X or Y chromosome, genes in the pseudoautosomal region are present on both chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal region are essential for normal development.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The X chromosome likely contains between 900 and 1,400 genes.

Genes on the X chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.
Biologists uncover mechanism that determines faithful inheritance of short chromosomes

Biologists uncover mechanism that determines faithful inheritance of short chromosomes

New test could be a ‘game changer’ in the treatment of chronic lymphocytic leukemia

New test could be a ‘game changer’ in the treatment of chronic lymphocytic leukemia

'Chromosome scanner' that protects against cancer identified

'Chromosome scanner' that protects against cancer identified

New blood test detects genetic disorders in fetuses

New blood test detects genetic disorders in fetuses

Study finds new genetic clues associated with asthma in African ancestry populations

Study finds new genetic clues associated with asthma in African ancestry populations

Researchers identify multiple genetic variants associated with body fat distribution

Researchers identify multiple genetic variants associated with body fat distribution

Conformance of genetic characteristics found to be crucial for longer preservation of kidney graft

Conformance of genetic characteristics found to be crucial for longer preservation of kidney graft

Study reveals how one mutation causes the most common inherited intellectual disability

Study reveals how one mutation causes the most common inherited intellectual disability

Researchers map extremely complex chromosome aberrations using DNA puzzle pieces

Researchers map extremely complex chromosome aberrations using DNA puzzle pieces

Researchers identify genes that make Staphyloccocus bacteria resistant to treatment

Researchers identify genes that make Staphyloccocus bacteria resistant to treatment

Researchers reveal novel computational tool used to analyze genetic variation

Researchers reveal novel computational tool used to analyze genetic variation

Zebrafish offers clue to alleviate gastrointestinal distress related to autism

Zebrafish offers clue to alleviate gastrointestinal distress related to autism

Cannabinoid receptor type 1 appears to be potential target to treat Down syndrome

Cannabinoid receptor type 1 appears to be potential target to treat Down syndrome

Study: BldC protein in Streptomyces acts as ‘brake’ to control timing of sporulation

Study: BldC protein in Streptomyces acts as ‘brake’ to control timing of sporulation

Large genetic analysis of impulsiveness reveals links with psychiatric disorders

Large genetic analysis of impulsiveness reveals links with psychiatric disorders

Study sheds light on the genetic causes of tumors in salivary glands

Study sheds light on the genetic causes of tumors in salivary glands

Researchers discover how transcription factors find specific loci within DNA

Researchers discover how transcription factors find specific loci within DNA

Study shows that aging and chronic diseases share common genetic factors

Study shows that aging and chronic diseases share common genetic factors

Big data opens door for characterizing immunity-related genome in Japanese population

Big data opens door for characterizing immunity-related genome in Japanese population

RNA-induced gene fusion can occur in mammalian cells, reveals study

RNA-induced gene fusion can occur in mammalian cells, reveals study