Delayed Inheritance and Lymnaea peregra

Abstract

Delayed inheritance is often confusingly described in Japanese textbooks of genetics : 1) Delayed inheritance of shell chirality is introduced with a Japanese name of Lymnaea japonica, although it has not been confirmed in Lymnaea except for L. peregra. 2) The mode of chirality inheritance tends to be called maternal inheritence, because of historical reasons. Maternal inheritance was first defined by Toyama (1913) as the mode of inheritance observed for serosa color of eggs of the domesticated silkmoth, Bombyx mori. The results of breeding experiments have evidenced his interpretation that maternal inheritance is a Mendelian mode of inheritance, which was later named delayed inheritance by Boycott et al. (1930). Although Boycott and Diver (1923) first reported the inheritance of shell coiling in Lymnaea peregra, it was Sturtevant (1923) who indicated that their results can be explained by maternal inheritance. According to his statement, Sturtevant (1923) apparently had accepted the term defined by Toyama (1913). However, Sturtevant and Beadle (1939) ignored the definition of both maternal inheritance and delayed inheritance and used maternal effect to refer to the inheritance of coiling chirality in L. peregra. Since then, maternal inheritance has been used as the equivalent to cytoplasmic inheritance, outside Japan. Today in genetics, maternal inheritance is commonly understood as cytoplasmic inheritance, even by Japanese geneticists. Then the mode of chirality inheritance should be distinguished from maternal inheritance in textbooks as well. However, it should be also noted as a historical fact that maternal inheritance was originally defined by Toyama (1913) to indicate the mode of delayed inheritance.