Which scientist is credited with the five basic rules of genetics?

• A. Gregor Mendel
• B. Charles Darwin
• C. Louis Pasteur
• D. James Watson

Answer: (A)

Gregor Mendel is the scientist whose work established the fundamental rules of genetics. By carefully cross-pollinating pea plants, he showed that traits are controlled by discrete units that exist in pairs, with one unit inherited from each parent. Some of these units mask others in the organism’s appearance (dominance), while the paired units separate during the formation of gametes so that each gamete carries only one unit for a given trait (segregation). When different traits are involved, the way these units are sorted into gametes is independent, leading to new combinations of traits in offspring (independent assortment). Finally, random fertilization means any sperm can unite with any egg, adding further variety to offspring. Taken together, these ideas form the five basic rules of genetics and explain why offspring show predictable patterns of inheritance. Other scientists made important contributions in related areas—Darwin explained evolution by natural selection, Pasteur advanced microbiology and germ theory, and Watson (with Crick) determined the DNA structure—yet Mendel’s systematic work first defined these inheritance rules.