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.
Using molecular targeting approach to kill melanoma cells

Using molecular targeting approach to kill melanoma cells

A love of coffee and tea is mostly genetic

A love of coffee and tea is mostly genetic

Researchers identify molecule to fight myotubular myopathy

Researchers identify molecule to fight myotubular myopathy

Reducing cellular proliferation could help deplete HIV reservoir and lead to a functional cure

Reducing cellular proliferation could help deplete HIV reservoir and lead to a functional cure

Non-coding genetic variant plays key role in endothelial function and disease incidence

Non-coding genetic variant plays key role in endothelial function and disease incidence

New study provides deeper insight into chromosome segregation during mitosis

New study provides deeper insight into chromosome segregation during mitosis

Failed DNA repair triggers chromosomal chaos in cancer cells

Failed DNA repair triggers chromosomal chaos in cancer cells

Cardiovascular and Alzheimer's disease share common genetics in some individuals, study shows

Cardiovascular and Alzheimer's disease share common genetics in some individuals, study shows

New way of identifying potential cancer drugs could streamline development of therapies

New way of identifying potential cancer drugs could streamline development of therapies

Scientists identify more aggressive chemotherapy treatment for childhood brain cancer

Scientists identify more aggressive chemotherapy treatment for childhood brain cancer

Scientists decode the longest ever continuous DNA sequence

Scientists decode the longest ever continuous DNA sequence

Down syndrome may hold important clues to onset of Alzheimer's disease

Down syndrome may hold important clues to onset of Alzheimer's disease

Researchers sequence two selfish genes in the fungus Neurospora intermedia

Researchers sequence two selfish genes in the fungus Neurospora intermedia

Common gene variants linked to migraine risk in African-American children

Common gene variants linked to migraine risk in African-American children

Genetic link to erectile dysfunction discovered

Genetic link to erectile dysfunction discovered

Study highlights opposite effects of gene following different types of environmental events

Study highlights opposite effects of gene following different types of environmental events

Research reveals how critical oocyte quality control process works

Research reveals how critical oocyte quality control process works

DFG establishes nine new Research Units

DFG establishes nine new Research Units

New research suggests power of zebrafish as tool for cancer drug discovery

New research suggests power of zebrafish as tool for cancer drug discovery

First U.S. patient treated with innovative gene therapy at Bascom Palmer Eye Institute

First U.S. patient treated with innovative gene therapy at Bascom Palmer Eye Institute