Choose the correct option:

Assertion [A]: Turner syndrome occurs only in females.

Reason [R]: Turner syndrome is characterised by X0 sex chromosomes.

The correct option is C

Assertion [A] is True and Reason [R] is True and is a correct explanation for [A].

Turner syndrome occurs when an individual has only one X chromosome and no corresponding Y or X chromosome. The total number of chromosomes in a cell would be 45 (44 autosomes + one X chromosome). The resultant individual is a sterile female in whom the presence of a solitary sex chromosome (X) leads to improper development of the secondary sexual characters. There may also be a lack of or delayed onset of puberty.