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.
Scientists explore interactions between chromosomes 12 and 17

Scientists explore interactions between chromosomes 12 and 17

Researchers identify gene enhancer that affects sex determination

Researchers identify gene enhancer that affects sex determination

Researchers discover protein responsible for X chromosome inactivation

Researchers discover protein responsible for X chromosome inactivation

Scientists shed light on key aspect of healthy cell division

Scientists shed light on key aspect of healthy cell division

Researchers discover three genes that may have contributed to evolution of large human brain

Researchers discover three genes that may have contributed to evolution of large human brain

Scientists develop new method to speed up genome evolution of baker's yeast

Scientists develop new method to speed up genome evolution of baker's yeast

Study establishes the importance of haploid cells

Study establishes the importance of haploid cells

Study reveals new protective mechanism for tumor cells in breast cancer

Study reveals new protective mechanism for tumor cells in breast cancer

Tau mutations may serve as novel risk factor for cancer

Tau mutations may serve as novel risk factor for cancer

Mapping the Genes Responsible for Pluripotency

Mapping the Genes Responsible for Pluripotency

CRISPR-Cas9-based strategy allows researchers to precisely alter hundreds of different genes

CRISPR-Cas9-based strategy allows researchers to precisely alter hundreds of different genes

Scientists disrupt two enzymes to shrink cancer cells

Scientists disrupt two enzymes to shrink cancer cells

Researchers harness the precision of CRISPR to knock out single genes in yeast

Researchers harness the precision of CRISPR to knock out single genes in yeast

Telomerase discovery paves way for drugs to combat aging and cancer

Telomerase discovery paves way for drugs to combat aging and cancer

Zika virus can be used for treating aggressive human central nervous system tumors, shows study

Zika virus can be used for treating aggressive human central nervous system tumors, shows study

Researchers target telomerase for killing NRAS-mutant melanoma cells

Researchers target telomerase for killing NRAS-mutant melanoma cells

Studies provide advanced knowledge about renal cancer

Studies provide advanced knowledge about renal cancer

Role of extrachromosomal pieces of DNA in cancer development and treatment resistance

Role of extrachromosomal pieces of DNA in cancer development and treatment resistance

Scientists identify gene responsible for evolution of recombination rates

Scientists identify gene responsible for evolution of recombination rates

Study proposes new mechanism that may contribute to gender differences in weight control

Study proposes new mechanism that may contribute to gender differences in weight control