Sex determination.

Bacci, Guido.

Date:: [1965]

Catalogue details

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

Credit: Sex determination. Source: Wellcome Collection.

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INTERSEXUALITY AND BALANCE THEORY OF SEX 113 Diploid gametophytes could not be obtained with Marchal's method in Sphaerocarpus: they are sometimes obtained through fusion of two haploid nuclei after the second meiotic division in spore formation. Such diploid spores (14 n + X + Y) gave mostly female gametophytes (Lorbeer, 1927) although Allen (1935) obtained hermaphrodite and female individuals in the course of his experiments on Sphaerocarpus donneili. The prevalence of a unisexual condition, which is observed in the sporophyte of Sphaerocarpus as in the diploid gametophytes of Musei, is accompanied by a considerable sex variability. The later work by Knapp (1935, 1939) and by Lorbeer (1936, 1938) also on Sphaerocarpus donneili lead to very interesting conclusions on the sex in the haploid phase although some problems have still been left unsolved. X-raying of spores and vegetation points of female gametophytes led to the production, both in Knapp's and in Lorbeer's experiments, of a number of male gametophytes. Knapp (1935) remarked that reversal from female to male is accompanied by the loss of a piece of the X chromosome and in a later paper (Knapp and Hoffmann, 1939) conclusively demonstrated that deletion of the X chromosome is not necessarily lethal, as contended by Lorbeer, and that, although even a very small deficiency is sufficient to induce reversal to the male sex in some regenerates, the number of male plants increases with the increase in size of the deficiency. These results can be explained with the alteration of the balance between the female factors in the X chromosome and male factors in the autosomes: the greater the defici¬ ency, the higher the possibility of eliminating female factors from the X chromosome. Certain experiments by Lorbeer suggest, however, the possibility of a different explanation: Lorbeer obtained monoecious individuals with 2X chromosomes. The so-called A mutant gametophytes develop antheridia and archegonia and they show a big fragment and a small spherical fragment of X: the В mutant gametophytes show only antheridia and no archegonia and cytological research demonstrates that only the big fragment of X is present. Lorbeer deduced that the big fragment of X is male determining and that the small spherical fragment is female determining. It was concluded therefore that male realizators in the big fragment are the result of a mutation from female to male genes and that the spherical fragment of X contains the origi¬ nal female genes. A monoecious С mutant was also obtained from the sterile clone of mutant B. This mutant showed male organs with unmotile spermatozoids in summer and normal archegonia in fall and in winter. A bigger and a smaller X chromosomes were present in such plants, the bigger probably corresponding to the masculinizing fragment of the В mutant the smaller being characterized by a marked bend in one arm. Fertihzation of such plants by spermatozoids from normal male gametophytes originated a group of plants showing the