November 14, 1919] 



SCIENCE 



459 



of the common substitutes. For homozygous 

 these are pure and pure-bred and for het- 

 erozygous, impure, mixed, hybrid, mongrel,^ 

 and cross-bred. These terms all designate, 

 rather loosely to be sure, types or methods of 

 mating or progeny of particular matings. 

 The objections to the appropriation of these 

 terms by Mendelists are many. Mendelists do 

 not hold that a knowledge of an individual's 

 origin is an accurate guide to its breeding 

 behavior; the terms indicate that they do. 

 The careless handling of these expressions 

 causes needless concern to those interested in 

 maintaining pure-bred stock, the very class of 

 persons with whom geneticists should set up 

 cordial relations. Confusion results from the 

 dual meanings since in spite of the attempted 

 re-definitions, it is still necessary for genetic- 

 ists to speak of the different types of mating 

 in the time-honored way. It is absurd to use 

 impure or hybrid in treating of sex-linked in- 

 heritance and other forms of obligatory het- 

 erozygosis associated with pure breeding. The 

 familiarity of these expressions make it ap- 

 pear that there is nothing particularly new in 

 the distinction between homozygosity and het- 

 erozygosity, the recognition of which is per- 

 haps the chief practical addition of genetics 

 to the breeder's store of ideas. The indict- 

 ment might be further extended, but enough 

 has been said to show that the objection to 

 these substitutes is not captious, but based on 

 practical considerations. 



I recognize that the use of these terms 

 began with the early Mendelian work on plant 

 material. The practise perhaps does not ap- 

 pear incongruous to the plant breeder, but it 

 is time that the well-meaning popularizer 

 should be made to realize that from the stand- 

 point of animal breeding these words have 

 much the same kind of appropriateness as 

 " registered " would have as a substitute for 

 homozygous and " grade " as a substitute for 



1 Not oomrn'on but used by Bateson on several 

 occasions, including Ms address as president of tlie 

 British Association for the Advancement of Sci- 

 ence (1914). Employment of this term in Amer- 

 ica -would add further to the undesirable implica- 

 tions owing to the bracketing of ' ' scrubs and mon- 

 grels" in the stallion laws of several states 



heterozygous. The sooner the misfits are 

 banished, the sooner will we see the spread of 

 ft sensible appreciation of genetics in live stock 

 circles. The need of discarding them far out- 

 weighs any possible inconvenience that would 

 result from the necessary use of homozygous 

 and heterozygous on all occasions, but the 

 task would be lightened if a satisfactory 

 series of alternatives were available for popu- 

 lar discussions. The object of this communi- 

 cation is to point out that by reviving and 

 extending a usage introduced by Mendel him- 

 self, we can readily secure such a series. 



Early in his 1865 paper, after demonstra- 

 ting the 3 : 1 ratio, Mendel makes his first dis- 

 tinction between homozygotes and heterozy- 

 gotes in these words : " Das dominirende 

 Merkmal kann hier eine doppelte Bedeutung 

 haben, namlich die des Stammcharakters oder 

 des Hybridenmerkmales." Throughout .the 

 paper he consistently refers to heterozygotes 

 as hybrids — thus giving rise to our own un- 

 fortunate practise — ^but as soon as he has 

 presented data showing the true nature of the 

 Fj ratio, he begins gradually to speak of the 

 homozygotes, whether dominant or recessive, 

 not as plants showing the parental character, 

 but as those having the special trait of re- 

 maining constant in successive generations. 

 " Sie besitzen nur constante Merkmale und 

 andern sieh in den nachsten Generationen 

 nicht mehr." His use of " constant " is indeed 

 so insistent as to suggest that he intended to 

 give to this adjective the technical meaning 

 we attach to homozygous. Certainly our 

 word might be substituted for his in passage 

 after passage without making the slightest 

 alteration in the sense or necessitating a 

 textual change. Moreover in one place at 

 least he makes constant a noun using it as the 

 precise equivalent of homozygote. My sug- 

 gestion is then that we follow Mendel in using 

 constant for homozygous and homozygote, but 

 that we use inconstant to replace his hybrid 

 in the sense of heterozygous and heterozygote. 

 The words constancy and inconstancy would 

 then be available for abstract discussions, and 

 if any one objected to the use of constant 

 and inconstant as substantives, he could adopt 



