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.
Extensive gene traffic, the process of genes leaving and arriving on the chromosome

Extensive gene traffic, the process of genes leaving and arriving on the chromosome

Scientists discover gene for Parkinson's disease

Scientists discover gene for Parkinson's disease

Genetic mutation raises interesting questions about the evolution of the Y chromosome

Genetic mutation raises interesting questions about the evolution of the Y chromosome

Autism gene discovered

Autism gene discovered

Surprises found In gene variation associated with schizophrenia

Surprises found In gene variation associated with schizophrenia

Researchers isolate gene responsible for Chron's disease

Researchers isolate gene responsible for Chron's disease

Completion of the sequencing of human chromosome 19

Completion of the sequencing of human chromosome 19

Launch of The Oxford Genetics Knowledge Park by Matt Ridley

Launch of The Oxford Genetics Knowledge Park by Matt Ridley

How rat's genetic blueprint stacks up against those of mice and humans

How rat's genetic blueprint stacks up against those of mice and humans

Gene-rich human Chromosome 19 sequence completed

Gene-rich human Chromosome 19 sequence completed

Discovery of new gene sheds light on human brain development

Discovery of new gene sheds light on human brain development

Scientists identify blood development gene which may aid the fight against cancer and leukemia

Scientists identify blood development gene which may aid the fight against cancer and leukemia

Gene Responsible for The Most Common Form of Diabetes

Gene Responsible for The Most Common Form of Diabetes