Gregor Mendel: His theory of characteristics in pea pod plants.

…

…the basis for the study of modern genetics, and are still recognized and used today. Why was Mendel not recognised? Mendel's ideas were not appreciated or recognised until the late 1900's mainly because he was a Roman Monk. This made people think he was 'different' from them like racism. Only until the late 1900's when people re-discovered his work, people realized his discoveries and it helped the theories and the study of modern genetics today.