Well.. first of all, it is a Monosomy. (meaning it lacks a choromosome, X specifically). The karyotype is 45,X. It comes from non-disjunction which is when a chromosome pair doesn't separate during meiosis, therefore one daughter will have two chromosome's from the mother, and another daughter will have nothing, and when the x-bearing sperm cell comes to fertilize, if he fertilizes the one with nothing, it will have 1 X, which in turn leads to Turner syndrome. The one with two chromosomes can lead to Kleinfelter syndrome which is XXY, because the male came and fertilized and now it has 3. Hope this helps.