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.
Researchers reveal central role of new key players in meiosis

Researchers reveal central role of new key players in meiosis

Popularity of non-invasive prenatal testing increasing among pregnant women

Popularity of non-invasive prenatal testing increasing among pregnant women

Researchers show how adult learning is impaired in females using mouse models of Rett syndrome

Researchers show how adult learning is impaired in females using mouse models of Rett syndrome

Natural pre-pregnancy progesterone benefits women with history of unexplained miscarriages

Natural pre-pregnancy progesterone benefits women with history of unexplained miscarriages

Roswell Park study provides new insights into gene mutations that can lead to cancer

Roswell Park study provides new insights into gene mutations that can lead to cancer

Archaeologist discovers 800-year-old genomes from bacterial infection in Byzantine skeleton

Archaeologist discovers 800-year-old genomes from bacterial infection in Byzantine skeleton

Northwestern Medicine scientists identify targeted molecular therapy that halts childhood leukemia

Northwestern Medicine scientists identify targeted molecular therapy that halts childhood leukemia

Potential drug could become first effective treatment option for Prader-Willi syndrome

Potential drug could become first effective treatment option for Prader-Willi syndrome

Experimental drug improves survival, growth outcomes in mouse model of Prader-Willi syndrome

Experimental drug improves survival, growth outcomes in mouse model of Prader-Willi syndrome

Researchers working to develop pill for inherited bleeding disorders

Researchers working to develop pill for inherited bleeding disorders

UC researchers uncover obesity-related protein's role in leukemia development

UC researchers uncover obesity-related protein's role in leukemia development

Researchers find new insights into silencing of X-chromosomes in human embryos

Researchers find new insights into silencing of X-chromosomes in human embryos

Genes that control immune system play key role in predisposition to HPV-related tumors

Genes that control immune system play key role in predisposition to HPV-related tumors

Researchers uncover first ‘off-switches’ for better control of CRISPR/Cas9 gene editing

Researchers uncover first ‘off-switches’ for better control of CRISPR/Cas9 gene editing

GWAS identifies genomic locations linked to personality traits and psychiatric disorders

GWAS identifies genomic locations linked to personality traits and psychiatric disorders

Scientists identify biomarkers to predict patient’s response to breast cancer treatment

Scientists identify biomarkers to predict patient’s response to breast cancer treatment

Alkaloid in ayahuasca beverage triggers neurogenesis in human neural cells

Alkaloid in ayahuasca beverage triggers neurogenesis in human neural cells

Study highlights requirement of protein in initiation of apoptosis in uveal melanoma

Study highlights requirement of protein in initiation of apoptosis in uveal melanoma

Research findings point to inherited genetic basis of ALL risk in children

Research findings point to inherited genetic basis of ALL risk in children

Starvation may shorten lifespans of children and male descendants, study suggests

Starvation may shorten lifespans of children and male descendants, study suggests