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Updated: May 15, 2025
Continuity of germplasm; The sex chromosome; The internal secretions and the sex complex; The male and the female type of body; How removal of sex glands affects body type; Sex determination; Share of egg and sperm in heredity; Nature of sex sexual selection of little importance; The four main types of secretory systems; Sex and sex-instincts of rats modified by surgery; Dual basis for sex; Opposite-sex basis in every individual; The Free-Martin cattle; Partial reversal of sex in man.
It occurs in the OEnothera mutant gigas. The origin of it has not been clearly made out, but it must result either from the splitting of each chromosome or from the omission of the chromosome reduction.
In two of these pairs the chromosomes are elongated and shaped like boomerangs, in the third they are small, round granules, and the fourth pair are the sex-chromosomes: in the female these last are straight rods, in the male one is straight as in the female, the other is bent. The straight ones are called the X chromosomes, the bent one the Y chromosome.
All the eggs contain what is known as the "X" type of sex chromosome. If an X unites with a Y, the result is a male. Since each combination happens in about half the cases, the race is about half male and half female. Thus sex is inherited, like other characters, by the action of the chromatin material of the cell nucleus.
It has been found that the twenty-two chromosome individual invariably develops into a female, and the twenty-one into a male. Therefore, femaleness is a positive quality, dependent upon the action of the X-chromosome, and maleness an absence of femaleness, due to lack of the extra, odd chromosome.
Selective fertilization with different kinds of sperm was impossible, since in these birds there is only one type of sperm two of eggs as to the sex chromosome. For instance, by overworking females at egg-production, the same birds which had been producing more males than females were made to reverse that relation.
The question remains, therefore, where are the factors of the somatic sex-characters? One suggestion which might be made is that the female characters are present in the Y, in this case female producing chromosome, or, if the female characters are merely negative, that the male characters are in the X chromosome, but only show themselves in the homozygous condition, thus:
In the pigeons, it was found that more yolk material tended to produce a larger proportion of females. The most minute quantitative measurements were made of this factor, to eliminate any possibility of error. The chromosome mechanisms practically force us to suppose that about half the eggs are originally predisposed to maleness, half to femaleness.
The parthenogenetic ovum of the bee is male, and yet it is an ovum capable only of producing spermatozoa. If the single X chromosomes is the cause of the development of spermatozoa in the male bee, why does it not produce spermatozoa in the gametes of the female bee, since when reduction takes place all these gametes have a single X chromosome?
If such a gamete is fertilised by a normal gamete the organism developed from the zygote will be heterozygous, and segregation will take place in its gametes between the chromosome carrying the factor and the other without it, so that there will now be many gametes destitute of the factor in question.
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