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Updated: June 14, 2025
This view is still maintained by those who differentiate two acts of fertilization within the embryo-sac, and regard that of the egg by the first male-cell, as the true or generative fertilization, and that of the polar nuclei by the second male gamete as a vegetative fertilization which gives a stimulus to development in correlation with the other.
When a gamete with 8 chromosomes unites in fertilisation with a normal gamete with 7 the zygote has 15.
The reproductive cells also undergo division and increase in number, and when they separate from the new individual and unite in fertilisation they still possess all the determinants of the fertilised ovum from which they are descended. Heredity thus continues from gamete to gamete, not from zygote to soma, and then from soma to gamete.
In this case, therefore, we have what Bateson was seeking, the origin of a new dominant character under observation, the original mutation having arisen in a single gamete of the zygote which gave rise to the plant.
After the meiotic or reduction divisions each gamete of course contains in its nucleus four single chromosomes. One of the four pairs consists of the sex-chromosomes.
The sex is thus determined by the male gamete, the X chromosome united with that of the female gamete producing female individuals, while the Y united with X produces male individuals. Professor T. H. Morgan has made numerous observations and experiments on a single culture of the fruit-fly, Drosophila ampelophila, bred in bottles in the laboratory for five or six years.
A dominant is something present which is absent in the recessive: the rose comb is due to a factor which is absent from the single. The two segregate in the gametes of the hybrid or heterozygote, and if a recessive gamete is fertilised by another recessive gamete the single comb reappears.
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