Name an event that restores the normal chromosome's number in the life stage?

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The event that restores the normal chromosome number in the life cycle is called fertilization.

In sexually reproducing organisms, gametes such as sperm and egg are formed by a special type of cell division known as meiosis. Meiosis reduces the chromosome number from diploid (2n) to haploid (n), meaning the gametes (sperm in males and eggs in females) contain only one set of chromosomes. This reduction is very important because if both parents contributed diploid sets during reproduction, the chromosome number would double in every generation, which would lead to genetic imbalance and abnormalities.

Fertilization is the process where the male gamete (n) fuses with the female gamete (n) to form a zygote (2n). This zygote contains a complete set of chromosomes, with one set coming from the mother and one from the father. In this way, the diploid number of chromosomes is restored, ensuring that the species maintains a constant chromosome number from one generation to the next.

For example, in humans, the haploid number is 23. During fertilization, the sperm with 23 chromosomes and the egg with 23 chromosomes fuse, forming a zygote with 46 chromosomes, which is the normal human diploid number. This diploid zygote then undergoes mitotic divisions to develop into a multicellular individual.

Besides restoring the chromosome number, fertilization also introduces genetic variation by combining genes from two different individuals. This variation is further increased by processes like crossing over and independent assortment during meiosis. Thus, fertilization is not only important for chromosome balance but also for the diversity and survival of the species.

Therefore, fertilization is a crucial event in the life cycle, playing a central role in both genetic continuity and variation, which are essential for reproduction, evolution and proper development.

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