What process results in the halving of chromosome number and produces diploid cells?

The process that results in the halving of chromosome number and produces haploid cells is meiosis, specifically Meiosis I. During this phase, homologous chromosomes are separated, reducing the chromosome number by half. This is crucial for sexual reproduction because it ensures that when gametes (sperm and egg) fuse during fertilization, the resulting zygote contains the appropriate diploid number of chromosomes, which is the full set for that organism.

In contrast, fertilization combines two gametes, each with a haploid number, restoring the diploid state rather than halving it. Mitosis is a cell division process that results in two identical diploid cells, keeping the chromosome number the same. Binary fission is a form of asexual reproduction seen primarily in prokaryotes, where a single cell divides into two identical cells, also maintaining the chromosome number rather than halving it. Thus, Meiosis I is the only process among the options that effectively reduces the chromosome number in producing haploid gametes necessary for sexual reproduction.