It is turner syndrome which is characterized by monosomy (2n-1) in only females. The genotype of the affected female is 45 + X_ . It is a chromosomal aberration in which the individual has 45 chromosomes instead of normal 46. It occurs due to non-disjunction during meiosis.
The person affected with turner's syndrome is dwarf, has less developed ovaries which leads to infertility and has heart defects.