Xkromosoomid

Xkromosoomid, Estonian term for X chromosomes, are one of the two sex chromosomes in many animals, including humans. In humans, females typically have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The X chromosome carries a large set of genes important for development and function beyond sex determination; by contrast, the Y chromosome contains fewer genes, many related to male development and fertility.

The human X chromosome is about 155 million base pairs long and contains roughly 800–900 protein-coding genes, distributed across its short arm (p) and long arm (q). It includes regions called pseudoautosomal regions (PAR) at the tips that can recombine with the Y chromosome during meiosis, helping to ensure proper chromosome pairing and segregation.

Inheritance and dosage compensation play central roles in X chromosome biology. A daughter receives one X from each parent, while a son receives an X from the mother and a Y from the father. To balance gene expression between XX females and XY males, one of the two X chromosomes in female cells is randomly inactivated early in embryonic development, forming a Barr body. Some genes escape this inactivation, resulting in mosaic expression of certain traits.

Evolution and clinical relevance are also notable. The X chromosome shares ancestry with autosomes, and recombination between X and Y is limited to the PAR regions. Mutations on the X chromosome can cause X-linked disorders, often more severe in males due to the single X copy. Examples include Duchenne muscular dystrophy and certain forms of color blindness. Sex chromosome anomalies, such as Turner syndrome (XO) and Klinefelter syndrome (XXY), illustrate the impact of chromosome number variation on development.