What process leads to a reduction in chromosome number during gamete formation?

Meiosis is the process that leads to a reduction in chromosome number during gamete formation. This specialized type of cell division occurs in sexually reproducing organisms and results in the production of gametes—sperm and eggs.

During meiosis, a diploid cell (with two sets of chromosomes) undergoes two successive divisions: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated, reducing the chromosome number from diploid to haploid. This means that each gamete produced contains only one set of chromosomes, which is essential for maintaining the species' chromosome number when fertilization occurs.

This reduction is crucial for sexual reproduction because it ensures that when the sperm and egg fuse during fertilization, the resulting zygote has the correct diploid chromosome number. In contrast, fertilization itself does not reduce chromosome numbers; rather, it combines them. Mitosis, on the other hand, maintains the chromosome number by producing identical daughter cells from a single parent cell, while binary fission is a form of asexual reproduction primarily observed in prokaryotes and also does not involve a change in chromosome number.