What is Meiosis

Cells divide for three main reasons: growth and development, replace worn-out or injured cells, and reproduction of offspring. Cell division is part of the cell cycle divided into five distinct phases. The diploid state of the cell is the normal chromosomal number in species. During sexual reproduction, the cell's chromosome number is reduced to a haploid state to ensure constancy in chromosome number and thus continuation of the species. The process of cell division is controlled by regulatory proteins. Mitosis occurs in all body cells and is divided into four phases. Meiosis, which occurs in only the germ cells involved in reproduction, divides the chromosomes in two rounds termed meiosis I and meiosis II (reduction division). The human lifecycle starts with gametogenesis, the process that forms gametes which then combine to form a zygote. The zygote quickly becomes an embryo and develops rapidly into a foetus. This chapter explores cell division.