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Glossary / History of genetics

Law of segregation

The rule that the two differing hereditary elements in a hybrid separate when egg cells and pollen are formed, so that each receives one or the other. Mendel set it out in 1866; it was rediscovered in 1900.

Mendel supposed that a hybrid forms, on average, equal numbers of egg cells carrying one parent's form and the other's, and the same for pollen. Since chance decides which pollen meets which egg, the hybrid's offspring split 1 : 2 : 1 (3 to 1 in appearance). When he put pollen from a wrinkled, green variety on a round, yellow hybrid, four kinds of seed came out in nearly equal numbers, 31, 26, 27 and 26, as the idea predicted[1].

Near the end of the paper Mendel wrote that in a hybrid the differing elements are in a temporary compromise and separate when the reproductive cells form. He was explicit that this was a hypothesis with little firm data behind it[1].

In 1900 Hugo de Vries reported the rule that traits split in the offspring of hybrids to the French Academy of Sciences[2], and gave his German paper the title "The law of segregation of hybrids" (Das Spaltungsgesetz der Bastarde)[3]. The same year Carl Correns wrote that Mendel had already set out the same rule[4].

Related terms

  • GeneWhatever is passed from parent to offspring and settles a hereditary trait. When Wilhelm Johannsen coined the word Gen in 1909, it was a name with nothing known behind it.
  • Dominant and recessiveIn a hybrid, the form of a trait that shows is called dominant and the one that stays hidden is called recessive. The terms are Mendel's own: dominirend and recessiv.

Sources

  1. G. Mendel, “Versuche über Pflanzen-Hybriden,” Verhandlungen des naturforschenden Vereines in Brünn 4, Abhandlungen 3–47 (1866).
  2. H. de Vries, “Sur la loi de disjonction des hybrides,” Comptes rendus de l'Académie des Sciences 130, 845–847 (1900).
  3. H. de Vries, “Das Spaltungsgesetz der Bastarde,” Berichte der Deutschen Botanischen Gesellschaft 18, 83–90 (1900).
  4. C. Correns, “G. Mendel's Regel über das Verhalten der Nachkommenschaft der Rassenbastarde,” Berichte der Deutschen Botanischen Gesellschaft 18, 158–168 (1900).