Turner syndrome is a chromosomal condition affecting females, caused by the complete or partial absence of one X chromosome. Instead of the usual two complete X chromosomes, affected individuals have only one fully intact X chromosome, with the second either missing entirely (monosomy X), structurally altered, or present in only some cells of the body (a pattern called mosaicism). This chromosomal difference occurs due to a random error during the formation of reproductive cells or in early embryonic cell division, and it is not caused by anything the parents did or did not do. Turner syndrome affects approximately 1 in 2,000 to 1 in 2,500 live female births, making it one of the more common chromosomal conditions.