What is the structure of the egg and sperm? How many chromosomes are there in these cells?

The most obvious distinguishing feature of an egg is its large size. A typical egg has a spherical or oval shape, and its diameter in humans is about 100 microns. The size of the nucleus may be equally impressive, in anticipation of rapid fission immediately following fertilization, protein stores are deposited in the nucleus. Another important specific structure of the egg cell is the outer egg membrane – a cover of a special non-cellular substance, consisting mainly of glycoprotein molecules, part of which is secreted by the egg itself, and the other part by the surrounding cells. In many species, the membrane has an inner layer directly adjacent to the plasma membrane of the egg and is called zona pellucida in mammals. This layer protects the egg from mechanical damage, in some eggs it also acts as a species-specific barrier for sperm, allowing only sperm of the same species or very close species to enter. All sperm have a large nucleus surrounded by cytoplasm, neck and tail, with which they can independently move. The egg and sperm have a haploid set of chromosomes.

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