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 103 sex determination in Lymantria may appear less clear than in Drosophila and the conventional values given sex genes in different races convey less striking evidence than the repetition of chromosomal units in Drosophila experiments. The concept of valence of sex determiners is nevertheless in agreement with the results in Drosophila. The dosage of male and female determining factors through crosses between races of different strengths allowed also a develop¬ mental analysis of the sex differentiating processes. The most striking demonstration that Y contains sex determining genes in certain species was obtained as a result of extensive researches on Meland- rium album, a seed plant of the pink family (Caryophyllaceae). Melandrium album and Melandrium rubrum are the only dioecious members of the group and the other species are monoecious. Winge and Blackburn found inde¬ pendently and in the same year (1923) the first example of sex chromosomes of angiosperms in Melandrium album. It is now certain (Westergaard, 1958) that the Y chromosome is the largest member of the pair (Fig. 5.6) according to the original Blackburn's interpretation. Fig. 5.6. Autosomes and sex chromosomes of Melandrium album : the Y is bigger than the X chromosome (Westergaard, 1948). 1. The Interaction between the Y, theX Chromosomes and the Autosomes Independent researches by Warmke (1939-1946), by Ohno (1939) and by Westergaard (1940-1959) first estabhshed that sex is not determined, as in Drosophila and in Rumex, by the ratio of X and autosomes, but is induced mainly, if not exclusively, by the interaction of the genes in the X and in the Y chromosomes. Normal females have two X and plants with two X and four sets of autosomes (instead of the normal two) are female. Plants with two X's and a Y develop into males and a single Y can suppress the female potentials of three X chromosomes in individuals with four sets of autosomes. Only when the ratio is shifted to Y/4Х, plants are bisexual in most ñowers of The Melandrium Case and the Sexual Fraction of Y