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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94 SEX DETERMINATION priately explored by Dobzhansky and Schultz might actually contain the F determiner and—at a time when the separation between pairing and differ¬ ential segments was not yet well realized—objected that a mechanism of multiple sex loci appears a poor thing for so constant a thing as sex determina¬ tion. The identity of the multiple factors with the sex factors acting on the sex balance mechanism was nevertheless maintained on the ground that the alleged modifying factors show the same quantitative relations as shown by the sex factors proper in the experiments by Bridges and that the segments of X show distinct additive action (Dobzhansky, 1935). Pipkin (1942) studied other dupUcation intersexes possessing 2X3A and substantially confirmed the previous experiments as the addictions of male segments produced small or no shifts in the female direction, and longer sections produced marked shifts in the same direction. It was remarked on the other hand that the part to the left of section 17 has more feminizing in¬ fluence than the part to the right. On the basis of this result, however, Goldschmidt (1955) still distinguished a modifying action of the small fragments from the primary sex determination of sufficiently large segments of the X chromosome. The distinction is derived on one hand from Goldschmidt's peculiar conception that assumes the existence of a hierarchical organization of the genetic material and on the other hand it is partially based on the idea that the heredity of sex is completely different from all others. Pipkin's experiments disproved nevertheless the possibility of the existence of a single female locus in Drosophila, a possibility that exists nevertheless in the sex determining mechanisms of other organisms. The problem of the distinction to be made between sex genes and sex modifying genes is still open for some cases. The term sex gene is replaced in most of the works on sex determination by terms such as sex modifier, sex determiner, sex factor or sex realizator with different implications which often disclose the authors' reluctance to regard the sex gene or the sex genes as ordinary genes. Goldschmidt (1955) clearly expressed this view by writing that the heredity of sex is completely diff'erent from all others. It is certain that some factors that have been discovered in the search for male genes in the autosomes of Drosophila are modifying genes and not sex genes. The possibility of the assimilation of sex modifiers to sex genes and consequently the connection between the heredity of sex and the heredity of other characters will be discussed later (see Chapter 12). 6. Autosomal Sex Genes and Modifiers A search for sex genes in the second chromosome of Drosophila melano- gaster was carried on by Pipkin (1947) using the translocation and triploid