Inheriting too many or not enough copies of sex chromosomes leads to atypical chromosome patterns, which can cause serious developmental complications. For example, males with an additional X chromosome (XXY) develop Klinefelter’s syndrome, which is a condition characterised by tall stature and, often, impaired fertility. Turner syndrome is another syndrome caused by an atypical chromosome pattern. Women with Turner syndrome have one X chromosome(X0), and are often very short, and do not undergo puberty. Some people with Turner syndrome also have kidney or heart problems.