Reginald Crundall Punnett (1875-1967)

Robinson M. Yost

Early Life

At the age of nine, Reginald Crundall Punnett, the eldest son of a middle-class builder, suffered a bout of appendicitis. This event forced him to rest daily and read among his father's natural history books, thereby sparking a lifelong interest in the study of living things. As a medical student at Cambridge University, Punnett excelled in the natural science tripos (honors examination), particularly in zoology.

Turning from medicine to evolutionary morphology, Punnett focused on the structure of a group of marine worms called nemerteans. After several years as a University of St. Andrews natural history demonstrator, he returned to Cambridge to become a Fellow of Caius College and later a Balfour Student in zoology.

Collaboration with Bateson

Early in the twentieth century, Gregor Mendel's work found a receptive audience among many biologists, including Punnett. In 1902, he wrote to the foremost British advocate of Mendel's laws, William Bateson, proposing experiments involving the inheritance of coat color. Shifting the focus of his studies, Punnett enthusiastically joined Bateson's genetics research group.

Between 1904 and 1910, Bateson and Punnett collaborated on hybridization experiments with sweet peas, domestic fowl, and other animals. Confirming and extending Mendelian genetics, their research established phenomena such as factor interaction, reversion, and complementary factors. Punnett also introduced a graphical method of representing hybrid crosses, now called the Punnett square. Punnett's textbook Mendelism (1905) introduced the subject to a wider audience. Appearing in many editions, this popular book was translated into seven different languages.

Butterfly Mimicry and Poultry Genetics

Punnett's interests also included the investigation of butterfly mimicry, the notion of one species mimicking another for adaptive advantage. Between 1912 and 1914, he debated Oxford entomologist, Edward Bagnall Poulton an firm believer in natural selection. Opposing Poulton, Punnett insisted that mimic species emerged as a result of discontinuous mutations rather than small continuous variations. Punnett's research in this subject culminated with Mimicry in Butterflies (1915).

Encouraging practical applications of genetics, Punnett served as an expert on poultry breeding during World War I. As wartime food shortages demanded economical measures, Punnett used sex-linked plumage colors to breed chickens of different colors according to sex. With this method, the large numbers of unwanted male chicks could be detected early and destroyed. Punnett's Heredity in Poultry (1923) remained the standard work on poultry genetics for several decades.

Later Work

In 1910, Punnett succeeded Bateson in the newly created Cambridge chair of biology. Two years later, this position became the Arthur Balfour Chair of Genetics, the first of its kind in Great Britain. Retiring in 1940, Punnett continued research in poultry genetics into the 1950's.

Later developments in genetic theory had little impact on Punnett's consistently Mendelian outlook. Methodologically, his work illustrates part of a broader shift in biology from descriptive field work to experimental laboratory research. Although best remembered for the Punnett square, he stands among a generation of scientists who established fundamental concepts in classical Mendelian genetics.


By Punnett

Mendelism, 1905 (first edition)

Mimicry in Butterflies, 1915

Heredity in Poultry, 1923

About Punnett

"Punnett, Reginald Crundall." F. A. E. Crew. Dictionary of Scientific Biography 11: 211-212

"Reginald Crundall Punnett." F. A. E. Crew. Biographical Memoirs of Fellows of the Royal Society 13 (1967): 309-326


Factor Interaction

Factor interactions occur when two or more factors, inherited independently, contribute to the determination of a single physical characteristic or phenotype.

Unit characters are ones in which inheritance is determined by a single pair of factors. When they segregate, each shows complete dominance. For example, Gregor Johann Mendel used clearly segregating unit characters in pea plants such as yellow or green, smooth or wrinkled, tall or short.

Yet, this pattern is not always the case. Frequently, more than one factor is involved in the expression of a phenotype. In breeding experiments with domestic fowl, Punnett and William Bateson found that more than one factor determines the inheritance of comb shape. Certain breeds of chickens have rose, pea, or single combs. Although most crosses yield familiar Mendelian ratios, Punnett and Bateson discovered that a rose bred with a pea resulted in a new comb shape called walnut in all the first-generation (F1) offspring.

Explaining the appearance of walnut-shaped combs, they conjectured that the independent inheritance of two factors determined comb shape. Hence, the presence of both dominant factors, R and P, resulted in walnut combs. The presence of only the R yielded rose combs, and the presence of only the P created pea combs. Single combs resulted from the absence of both dominant factors. Furthermore, the interaction explained why crossing chickens with walnut combs yielded a 9:3:3:1 ratio, with nine walnut combs to three rose combs to three pea combs to one single comb, in the second-generation (F2) offspring [see figure].

Many other types of factor interactions occur. Bateson and Punnett extended the explanatory power of Mendelism by establishing this important concept.


The Science of Biology, an Introductory Study. George G. Scott. New York: Thomas Y. Crowell Company, 1930 (Revised Edition)

Principle of Genetics. Eldon J. Gardner. New York: John Wiley & Sons, Inc., 1972 (Fourth Edition)