Answer:
Turner syndrome occurs when one of the X chromosome is missing in female cells causing karyotype XO.
(Options are not given in the question)
Explanation:
Normally all the human beings have 2 sex chromosomes in each cell. Males has X and Y chromosomes while females has 2 X chromosomes in each cell for normal functioning of cells. While in turner syndrome, one normal X chromosome is missing or structurally altered thus giving the karyotype XO due to chromosomal nondisjunction.