Why does the sex ratio in populations at different stages of the life cycle of individuals change?

In natural populations, during sexual reproduction at the time of fertilization, the ratio of zygotes by sex, as a rule, is close to 1: 1 – this is the primary sex ratio. In the future, the sex ratio at the embryonic stage may vary depending on various environmental factors. In the embryonic period, the influence of environmental factors is superimposed on the genetic condition of the sex, which leads to the formation of a secondary sex ratio. By the time of puberty, the sex ratio changes and a tertiary sex ratio is formed. It depends on the resistance of individuals of different sexes to environmental factors, which is associated with physiological, environmental, behavioral and other characteristics of males and females.

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