Final answer:
Gregor Mendel's significant contribution to genetics was demonstrating that traits are inherited from parents to offspring in a predictable manner, known as Mendelian genetics.
Step-by-step explanation:
Gregor Mendel's contribution to genetics is c.) the discovery that traits are passed from parent to offspring in predictable ways. Mendel's experiments with pea plants were foundational in illustrating how physical characteristics are transmitted from one generation to the next through what he termed as dominant and recessive traits. While working in the mid-1800s, long before the discovery of genes or chromosomes, Mendel meticulously crossed pure-breeding pea plants with specific differing traits and analyzed their offspring. This led to what we now call Mendelian genetics, which laid the groundwork for our current understanding of heredity and the chromosomal basis of inheritance.