The Mutual Similarity of the F₁-Individuals

Abstract

With regard to the exactitude of the rule concerning the uniformity of the F₁-individuals, it seems that there existed only a slight difference in view-point between investigators prior to 1900. For example, Gaertner (1849, p. 237) believed that “there originated from seeds produced by a cross between two species, which breed true to type, plants of one definite type, which resemble one another completely. There sometimes also occurs (however seldom) among the seedlings, from one and the same hybridization, (that is to say, from seeds from one and the same fruit) alongside a great number of hybrid plants of wholly the same normal hybrid type, some which show very aberrant forms and shapes. We will call these aberrations “exceptional types”, since they occur only in very small numbers, indeed often only as one specimen”. Naudin (1865, p. 146–147) gave these statements: “I have always found that the hybrids which I have obtained myself and whose origin was well known to me, had a great mutual uniformity with other individuals of the first generation which also originate from the same cross, regardless of the number of individuals” and “To put it into a few words, the hybrids of one and the same cross mutually resemble one another in the first generation, precisely or nearly so, as do individuals originating from one and the same pure species”. Mendel found in his hybridization of peas a very clear mutual resemblance in the F₁-individuals: “In Pisum, the hybrids obtained directly from hybridization of two types, in all cases have the same external appearance, but their offspring are variable and indeed, change according to definite rules” (1869, p. 31).