Sex determination.

  • Guido Bacci
Date:
[1965]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Sex determination. Source: Wellcome Collection.

    190/328 page 174
    174 SEX DETERMINATION carried on by v. Dehn (1950, 1955) in a series of researches on the cladoceran Moina rectirostris and completely phenotypical sex determination was assumed for this heterogonic species as for other species of cladocerans. New researches (Bacci et ah, 1961) on the maturation of the parthenogetic eggs permit, however, adiflferent interpretation which will be discussed in Chapter 11. The most interesting among the external sex determining factors appear to be the hormone-like substances whose existence has been first suggested in the experiments on Bonellia; and later in Ophryotrocha and lone experiments. The recent observations by Müller that contact is necessary in Ophryotrocha casts, however, some doubt about the mode of action of such substances. A sex determining influence of the Bonellia type has also been suggested for Mytili- cola and for Paramermis. Although such influences appear to be extremely important because they are active in the normal life cycle of the species almost nothing is known about the chemical nature of the substances involved, about their specificity and about their mode of action. Much more investi¬ gation is needed in this field. It appears meaningless to try to evaluate the importance of environmental influences on sex determination. It is nevertheless necessary to point out once more that even in animals where sex digamety has been established both through cytological and genetical methods, sex inversion and alterations of sex ratios have been obtained by means comparable to those mentioned above. For this reason it is not justified to draw any definite conclusion regarding the sex genotype from experiments that show the influence of the environment on the individual sex phenotype leaving out of consideration sex variation and its inheritance in the progeny (Bacci, 1950a). In other words the validity of the FFMM formula cannot be proved through the study of environmental in¬ fluences alone. 2. The Sex Genotypes The discovery of the high sex variability in Patella led to the realization of two important facts. (a) Some hermaphrodite species are composed of a majority of hermaphro¬ dite and of a few pure male and pure female individuals and it was assumed that from such species both purely (balanced) hermaphrodite species and gonochoric species (Bacci, 1947a, c) can be developed. (b) Some gonochoric species that show labile gonochorism can be assimi¬ lated with unbalanced hermaphrodite species from the point of view of sex variability (Bacci, 1947b). Such facts led Montalenti and the author of the present book to advance a general theory to explain both the sex gradations of unbalanced hermaphro¬ dite species and of Bonellia type labile gonochorists (Bacci, 1949b; Monta¬ lenti, 1950; Bacci, 1950; Montalenti and Bacci, 1951).
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