Lucien Cuénot

Lucien Cuénot (1866-1951) was a French biologist. In the first half of the 20th century, Mendelism was not a popular subject among French biologists. Cuénot defied popular opinion and shirked the “pseudo-sciences” as he called them. Upon the rediscovery of Mendel's work by Correns, Devries, and Tschermak, Cuénot proved that Mendelism applied to animals as well as plants.

Cuénot L. La loi de Mendel et l'hérédité de la pigmentation chez les souris. Arch. Zool. Exp. Gen. Ser. 3, vol 10, pages xxvii-xxx. (1902).

Cuénot's experiments
Cuénot spent two years working on mice and came to the conclusion that three “mnemons” (genes) are responsible for the production of one “chromogen” or pigment and two “distases” enzymes. The pigment (if present) is acted upon by the enzymes to produce black or yellow colour. If no pigment is present the result is an albino mouse. Cuénot studied the offspring of various crosses between mice and concluded that these “mnemons” or genes were inherited in a Mendelian fashion.

Cuénot L. L'hérédité de la pigmentation chez les souris. Arch. Zool. Exp. Gén. Ser. 4, vol 1, pages xxxiii-xli. (1903).

Subsequently, Cuénot was the first person to describe multiple allelism at a genetic locus.

He also described a lethal mutation in the mouse agouti locus at a time when such a mutation was unheard of.

Cuénot L. Les races pures et leurs combinaisons chez les souris. Arch. Zool. Exp. Gén. Ser. 4, vol 3, pages cxxiii-cxxxii. (1905)

A voice unheard?
There is some argument over the degree of recognition of Cuénot's pioneering work in his own day, and up until the present.

Some scientists who were famous in Cuénot's day such as William Bateson, the man credited the “one gene one enzyme” hypothesis never recognized Cuénot's discovery that certain traits arose due to the presence or absence of an enzyme. Archibald Garrod suggested in the early part of the 20th century that certain diseases occurred in the absence of an essential enzyme in a biochemical pathway and that these diseases were inherited as Mendelian recessives. Garrod failed to mention Cuénot in his work. At this time, there was widespread difficulty with reconciling genetics and biochemistry.

Failure of Bateson and Garrod to mention Cuénot's pioneering work on the one-gene one-enzyme hypothesis does not take away from the fact that it was pioneering work. Such failure to credit pioneering work would constitute scientific misconduct in the present day. That Cuénot's articles were in French may be the reason for Bateson's and Garrod's insular view.

Other scientists who were well-known in Cuénot's own day and still into the present day, such as Clarence Little and Sewall Wright, and William E. Castle did credit Cuénot with pioneering work in genetics.

For example Clarence Little and William E. Castle did credit Cuénot with the disovery of the first lethal mutation.

W.E. Castle, and C.C. Little. On a modified Mendelian ratio among yellow mice. Science 32, 868-870. (1910).

The mouse geneticist Clarence Little did credit Cuénot with the idea and first evidence for multiple allelism, and recognizing that the inheritance of white spotting in the mouse did not breed true.

A note on multiple allelomorphism in Mice. C.C. Little. American Naturalist, 49, 122-125. (1915). The inheritance of black-eyed white spotting in mice. C.C. Little. American Naturalist, 49, 727-740. (1915).

The mouse and population geneticist Sewall Wright did credit Cuénot with the discovery of multiple alleles and the one-gene one-enzyme hypothesis.

Color inheritance in mammals. II The mouse-better adapted to experimental work than any other mammal-Seven sets of Mendelian Allelomorphs (alleles) identified-Factorial hypothesis framed by Cuenot on basis of his work with mice. J. Hered. 8,373-378. (1917).

When writing Cuénot's obituary in 1951 Richard Goldschmidt does credit Cuénot with the gene controlling enzyme hypothesis:

"In 1903 he (Cuénot) already understood the genic (genetic) control of pigment in terms of chromogen (genes were responsible for the chromogen) and oxydase (enzyme)."

L. Cuénot: 1866-1951. Richard Goldschmidt. Science 113,309-310. (1951).

John Cairns as recently as 2003 credited Lucien Cuénot with the one-gene one-enzyme hypothesis.

The centenary of the one-gene one-enzyme hypothesis. M. Hickman and J. Cairns. Genetics 163,839-841 (2003).

The entry in the 1911 Encyclopaedia Britannica, which may be taken as the work of reference for the educated man or woman of that time does fully appreciate Cuénot's work on the relationship between determinants (genes) and ferments (enzymes).

http://1911encyclopedia.org/Albino

“ Before we can inquire into the cause and meaning of albinism it will be necessary first to consider the nature of pigmentation. It has recently been ascertained that the coloration of certain sponges is due to the interaction of an oxydizing ferment (enzymes), tyrosinase, upon certain colourless chromogenic substances. In 1901, Otto v. Furth and Hugo Schneider showed that a tyrosinase could be obtained from the blood of certain insects, and, acting upon a chromogen present in the blood, converted it into a pigmentary substance of melanin-like nature. Hans Przibram also extracted a tyrosinase ' from the ink-sac of Sepia, and, causing it to act upon a watery solution of tyrosin, obtained a black pigment. From the blood of Bombyx mori, V. von Ducceshi has also obtained a tyrosinase. Subsequently (1903) L. Cuénot, in order to explain certain features in the hereditary transmission of coat colour in mice, postulated the hypothesis that the grey colour of the wild mouse (which is known to be a compound of black, chocolate and yellow pigments) may be due either to the interaction of a single ferment and three chromogens, or vice versa, to one chromogenic substance and three ferments.”

“In spite of the inquiry being only in its initial stages, there is already good evidence to believe that Cuénot's theory is correct, and that an albino is an individual whose skin lacks the power to secrete either the ferment or the chromogen. It forms one but not both of these substances.”

“Not only do albinoes thus carry the determinants (genes) for pattern, but it has been known for some time that they also carry gametically, but never visible somatically, the determinants (genes) for either the ferment (enzyme) or the chromogen (substrate) for one or more colours. L. Cuénot was the first to show this for albino mice.”

Cuénot is in some ways responsible for his lack of acknowledgment. The symbolism he used in experiments described phenotype rather than genotype and were quite confusing. (Toda'’s crosses are described in terms of genotype.) His studies on mice were also cut short when German troops invaded the town of Nancy, where he kept his mouse colony. After the war he never returned to his studies on mice and settled for the less controversial subjects of zoology and physiology.