Final answer:
Johann Gregor Mendel, a 19th-century scientist, carried out important studies on heredity using pea plants. His work forms the basis of classical genetics, demonstrating that genes are the units of inherited information.
Step-by-step explanation:
During the 19th century, long before chromosomes or genes had been identified, Johann Gregor Mendel set the framework for genetics by studying a simple biological system, the garden pea. He conducted methodical, quantitative analyses using large sample sizes. Mendel's work laid the foundation for the fundamental principles of heredity. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capacity to be replicated, expressed, repressed, modified and mutated. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. Genes do not all obey the tenets of Mendelian genetics, but Mendel's experiments serve as an excellent starting point for thinking about inheritance.