Describe the fertilization process and the initial stages of embryo development.

Fertilization consists in the fusion of the nuclei of the sperm and the egg, this process takes place in the fallopian tube. The egg is surrounded by many sperm and begins to secrete enzymes that destroy the protective layers of the egg. After the penetration of one sperm, the egg membrane becomes impenetrable for other male gametes. When the paternal and maternal chromosomes merge, a zygote with 46 chromosomes is formed and multiple division begins, leading to the formation of a multicellular spherical embryo, which gradually moves into the uterus and penetrates into its mucous membrane.

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