Reginald Punnett became a zoology enthusiast during his years at Caius College in Cambridge. He studied nemertines (worms), wrote a dozen papers on the subject, and even had a few species of worms named after him. In 1904, Punnett read a report about genetics research and became interested in the budding field. Punnett wrote to William Bateson, an English geneticist, about pursuing a certain line of inquiry. Bateson, who was then researching Gregor Mendel's newly rediscovered theories, asked Punnett to collaborate. The pair worked to prove the Mendelian factors that had so intrigued Bateson since 1900. Using domestic chickens and sweet pea plants, they were able to confirm and extend Mendel's findings and explain phenomena such as sex determination, gene linkage (the simultaneous inheritance of more than one characteristic), and mimicry.

Punnett was a gentle, quiet man who never sought fame. The slow, methodical nature of the experiments suited him nicely. And although Bateson dominated the six-year partnership, Punnett made his own important contributions to the science of genetics. In 1905, he published Mendelism, a scientifically important and commercially popular book that clearly stated the principles of heredity according to Mendel. In Mendelism, Punnett presented a simple diagram to demonstrate the offspring expected when a pair of organisms possessing one or two particular sets of traits are mated. Now known as Punnett's square, the diagram has been used for decades to teach genetics to beginning students.

Punnett's achievements were recognized in 1910, when he succeeded Bateson as professor of biology at the University of Cambridge. The University soon named Punnett the Arthur Balfour Professor of genetics--the first position of its kind in the United Kingdom--which he held until his retirement in 1940. Punnett did much to promote Mendelian genetics in the scientific community through the Journal of Genetics, which he edited for 35 years. He also introduced genetic principles to the general public, particularly livestock breeders, for whom his work proved to be very useful.