[The human genome--chromosome X. Focus on Xq28]

The human chromosome X is one of those studied in greatest detail. It contains the genes for a large number of severe hereditary diseases. Several unusual mutation mechanisms, such as the expansion of trinucleotide repetition, were detected on chromosome X. Other peculiarity which differentiate this chromosome from autosomes is the phenomenon of inactivation of one of two copies of chromosome X in women. Adjacent to the telomeres of both arms of chromosome X are pseudoautosomal region which make pairing of chromosomes X and Y during male meiosis possible. The difference in the dosage of X-linked genes on both sexes and the mechanism of its compensation result in the considerable interspecific evolutional conservation of chromosome X in mammals. The chromosomal area Xq28 which contains many genes and in which a large number of human hereditary diseases are mapped serves as a model area for investigations of chromosome X and the whole human genome.