In theology, agenesis means to have no beginning or to have no creator, to come into existence without the influence of an outside intelligence.

Phocomelia- failure of the arms or legs to develop.

Renal agenesis- failure of one or both of the kidneys to develop.

In medicine, agenesis refers to the failure of an organ to develop during embryonic growth and development. Many forms of agenesis are referred to by individual names, depending on the organ affected:

Agenesis of the corpus callosum- failure of the Corpus callosum to develop.

Penile agenesis- failure of penis to develop.