X chromosome

The X chromosome is one of the two human sex chromosomes and carries genes including the long- and medium-wavelength cone opsins.

Chromosome: A DNA molecule packaged with proteins that carries genetic information in a cell. The X chromosome is one member of this broader class of genetic structures.
Barr body: A condensed, largely inactive X chromosome visible in the nucleus of many mammalian cells. It is the compact cellular form of an X chromosome silenced by X-inactivation.
Red–green color blindness: A group of color-vision deficiencies caused mainly by altered or missing long- or medium-wavelength cone opsins. The relevant opsin genes lie in a repeated array on the X chromosome.
Y chromosome: The human sex chromosome that carries the SRY gene and has a smaller gene content than the X chromosome. Its distinct gene content and inheritance contrast with those of the X chromosome.
Gene: A DNA sequence that contributes to a functional product, such as an RNA molecule or protein. Genes distributed along the X chromosome encode many of its biological effects.
Pseudoautosomal region: A region shared by the X and Y chromosomes where they can pair and recombine. These regions let X and Y chromosomes exchange DNA during male meiosis.
Opsin: A light-sensitive protein that combines with a chromophore to form a visual pigment. The X chromosome carries the genes for the long- and medium-wavelength cone opsins.
SRY: A gene that usually initiates testis development in humans and other mammals. Unlike SRY, which is on the Y chromosome, many sex-related genes are X-linked.
Allele: One of two or more alternative DNA sequences at a particular genomic location. Different X-linked alleles can produce distinct traits and disease risks.
Escape from X-inactivation: Expression of genes from an X chromosome that is otherwise subject to inactivation. Some X-linked genes remain active on the silenced chromosome, affecting dosage.

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