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.
CHOP experts identify new autoimmune disorder along with personalized treatment for young patient

CHOP experts identify new autoimmune disorder along with personalized treatment for young patient

MGH researchers explore how genetic abnormality in Ewing sarcoma unleashes tumor growth

MGH researchers explore how genetic abnormality in Ewing sarcoma unleashes tumor growth

Researchers identify genes linked to childhood nephrotic syndrome

Researchers identify genes linked to childhood nephrotic syndrome

Answer to decades-old mystery may allow some children to avoid bone marrow transplantation

Answer to decades-old mystery may allow some children to avoid bone marrow transplantation

New mouse model shows great promise for Rett syndrome research

New mouse model shows great promise for Rett syndrome research

Researchers study whole genome sequences of human induced pluripotent stem cells

Researchers study whole genome sequences of human induced pluripotent stem cells

Mutated gene linked to 3-year-old girl's severe neurological symptoms

Mutated gene linked to 3-year-old girl's severe neurological symptoms

Researchers uncover cause for progression of prostate cancer to incurable stage

Researchers uncover cause for progression of prostate cancer to incurable stage

Researchers raise viability of cloned mice using somatic cell nuclear transfer method

Researchers raise viability of cloned mice using somatic cell nuclear transfer method

Study findings highlight importance of early detection of SMA through newborn screening

Study findings highlight importance of early detection of SMA through newborn screening

Researchers solve mystery of final blood group system

Researchers solve mystery of final blood group system

Research sheds on how new species may arise from rapid mitochondrial evolution

Research sheds on how new species may arise from rapid mitochondrial evolution

New findings refine link between clonal hematopoiesis and blood cancer risk

New findings refine link between clonal hematopoiesis and blood cancer risk

Researchers uncover molecular drivers of  a deadly pediatric cancer

Researchers uncover molecular drivers of a deadly pediatric cancer

Researchers unmask functioning of protein involved in DNA repair during spermatogenesis

Researchers unmask functioning of protein involved in DNA repair during spermatogenesis

Researchers discover biomarkers that accurately identify hypervirulent K. pneumoniae

Researchers discover biomarkers that accurately identify hypervirulent K. pneumoniae

Study explains why men are more at risk for neurodevelopmental disorders

Study explains why men are more at risk for neurodevelopmental disorders

Genes associated with autism interact to modulate variable symptoms of disease

Genes associated with autism interact to modulate variable symptoms of disease

Hearing partially restored in deaf lab mice using novel therapy

Hearing partially restored in deaf lab mice using novel therapy

USC study reveals how the cell launches emergency response to repair damaged DNA

USC study reveals how the cell launches emergency response to repair damaged DNA