Xkromosoomi

Xkromosoomi, in the context of human genetics, refers to the X chromosome, one of the two sex chromosomes in humans and many other mammals. It is a large, gene-rich chromosome that pairs with the Y chromosome to determine sex and contributes to a broad range of traits and developmental processes. In humans, individuals typically have 46 chromosomes; females usually carry two X chromosomes (46,XX) and males one X and one Y (46,XY).

Structure and genes: The X chromosome is about 155 million base pairs long and contains roughly 800-900 genes. It carries many genes essential for development, nervous system function, and metabolism. Parts of the chromosome, called pseudoautosomal regions PAR1 and PAR2, recombine with the Y chromosome during male meiosis, helping to ensure proper segregation of sex chromosomes.

Dosage compensation and inactivation: In female cells, one X chromosome is largely silenced to balance gene expression with males, a process called X-inactivation. This is mediated by the XIST gene and results in a Barr body. Some genes escape inactivation and can contribute to sex-specific traits.

Inheritance and disease: Because females have two X chromosomes while males have one, X-linked traits show distinctive patterns. Disorders on the X chromosome, such as hemophilia A and B and red-green color vision deficiency, are more common in males. Duchenne muscular dystrophy and Rett syndrome are also linked to X-linked genes. Aneuploidies involving the X, such as Turner syndrome (45,X) and Klinefelter syndrome (47,XXY), affect development and fertility.

Evolution and research: The X chromosome has evolved to pair with the Y in the PAR regions and to accumulate genes with dosage-sensitive roles. It remains a central focus of research in genetics, developmental biology, and medicine, due to its unique inheritance, regulation, and association with numerous inherited conditions.