Final answer:
Gregor Mendel demonstrated how recessive traits reappear in a predictable way through controlled crosses.
Step-by-step explanation:
One significant discovery made by Gregor Mendel is that he demonstrated recessive traits "reappear" in controlled crosses in a mathematically predictable way. Mendel's experiments with garden peas allowed him to observe how genetic traits are passed on from one generation to another. Through his careful observations and analysis, Mendel formulated the laws of inheritance, known as Mendelian genetics.
Learn more about Gregor Mendel's significant discovery