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 uncover new role of heterochromatin in maintaining chromosomal integrity

Researchers uncover new role of heterochromatin in maintaining chromosomal integrity

Cellular recycling process may prevent cancer initiation, finds study

Cellular recycling process may prevent cancer initiation, finds study

Study sheds new light on male infertility

Study sheds new light on male infertility

New research focuses on noise sensitivity and general fearfulness of canine behavior

New research focuses on noise sensitivity and general fearfulness of canine behavior

Experimental drug can positively modify key characteristic behavior in FXS patients

Experimental drug can positively modify key characteristic behavior in FXS patients

Scientists aim to find genetic causes of developmental abnormalities in the vagina and uterus

Scientists aim to find genetic causes of developmental abnormalities in the vagina and uterus

Unexpected connection found between feeding and memory centers of the brain

Unexpected connection found between feeding and memory centers of the brain

Researchers discover how cancer cells avoid genetic meltdown

Researchers discover how cancer cells avoid genetic meltdown

Researchers identify genetic risk factor for atypical heart attack in women

Researchers identify genetic risk factor for atypical heart attack in women

European scientists aim to identify causes of dementia

European scientists aim to identify causes of dementia

Researchers uncover genes that play a key role in the inactivation of X chromosomes

Researchers uncover genes that play a key role in the inactivation of X chromosomes

New compound blocks genetic cause of familial ALS and frontotemporal dementia

New compound blocks genetic cause of familial ALS and frontotemporal dementia

Folate deficiency creates more damaging chromosomal abnormalities than previously known

Folate deficiency creates more damaging chromosomal abnormalities than previously known

Geneticists discover how sex-linked disorders arise

Geneticists discover how sex-linked disorders arise

MUHC's 'Dr. House' discovers new genetic disease and the gene responsible for it

MUHC's 'Dr. House' discovers new genetic disease and the gene responsible for it

Study reveals how the absence of Dna2 enzyme affects chromosome instability

Study reveals how the absence of Dna2 enzyme affects chromosome instability

New massive sequencing platform implemented for double factor preimplantation genetic testing

New massive sequencing platform implemented for double factor preimplantation genetic testing

Researchers reveal previously unknown genetic effect that can raise or reduce risk of heart disease

Researchers reveal previously unknown genetic effect that can raise or reduce risk of heart disease

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