Meiosis Study Guide

In meiosis, pairs of homologous chromosomes (orange) are pulled to opposite ends of the cell by spindles (blue). This results in two cells with half the usual number of chromosomes. Meiosis occurs only in the sex cells. Credit: TIM VERNON/SCIENCE PHOTO LIBRARY/Getty Images

Overview of Meiosis

Meiosis is a two-part cell division process in organisms that sexually reproduce. Meiosis produces gametes with one half the number of chromosomes as the parent cell. In some respects, meiosis is very similar to the process of mitosis, yet it is also fundamentally different from mitosis.

The two stages of meiosis are meiosis I and meiosis II. At the end of the meiotic process, four daughter cells are produced. Each of the resulting daughter cells has one half of the number of chromosomes as the parent cell. Before a dividing cell enters meiosis, it undergoes a period of growth called interphase.

During interphase the cell increases in mass, synthesizes DNA and protein, and duplicates its chromosomes in preparation for cell division.

Meiosis I

Meiosis I encompasses four stages:

Meiosis II

Meiosis II encompasses four stages:

At the end of meiosis II, four daughter cells are produced. Each of these resulting daughter cells is haploid.

Meiosis ensures that the correct number of chromosomes per cell is preserved during sexual reproduction. In sexual reproduction, haploid gametes unite to form a diploid cell called a zygote. In humans, male and female sex cells contain 23 chromosomes and all other cells contain 46 chromosomes. After fertilization, the zygote contains two sets of chromosomes for a total of 46. Meiosis also ensures that genetic variation occurs through genetic recombination that happens between homologous chromosomes during meiosis.

Stages, Diagrams, and Quiz