female intimate characteristics are substituted for male ones, or vice versa.
What's the substitution process all about?
Its as a result of sequential hermaphroditism observed in some species.
What's hermaphroditism?
It can change from a male to female (protandry), or from female to male (protogyny) or from female to hermaphrodite 
Any genetically related?
Sex change
Sex change is a process by which a person or animal changes sex – that is, by which female sexual characteristics are substituted for male ones or vice versa. Sex change may occur naturally, as in the case of the sequential hermaphroditism observed in some species. Most commonly, however, the term is used for sex reassignment therapy, including sex reassignment surgery, carried out on humans. It is also sometimes used for the medical procedures applied to intersex people. The term may also be applied to the broader
a certain age or size.
In animals, the different types of change are male to female (protandry), female to male (protogyny), female to hermaphrodite (protogynous hermaphroditism), and male to hermaphrodite (protandrous hermaphroditism). Both protogynous and protandrous hermaphroditism allow the organism to switch between functional male and functional female. These various types of sequential hermaphroditism may indicate that there is no advantage based on the original sex of an individual organism. Those that change gonadal sex can have both female and male germ cells