Define a vestigial organ?

is often poorly defined, most commonly because someone has chosen a poor source to define the term. The Oxford English Dictionary (OED) defines vestigial organs as organs or structures remaining or surviving in a degenerate, atrophied, or imperfect condition or form

answer:

sequence 1- deletion

                  2- duplication

                  3- insertion

                  4- substitute

                  5- inversion