Photo shows pea-plant flower, with purple petals that fold back on themselves.
Figure 12.1 Experimenting with thousands of garden peas, Mendel uncovered the fundamentals of genetics. (credit: modification of work by Jerry Kirkhart)

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.

An understanding of genetic inheritance enables scientists to study and explain complex phenomena. For example, scientists studied the remains of 84 ancient dogs from North and South America. They found that some of the dogs had greater genetic diversity, indicating that these dogs might have interbred with American wolves. Other dogs in their sample had low diversity, indicating that ancient humans were purposely breeding dogs. The study also found that dogs migrated to the Americas with humans only about 10,000 years ago. You can read more about this fascinating story here.