Key terms

TermMeaning
GameteA sex cell (in humans: sperm for males, and eggs for females)
MeiosisA two-step process of cell division that is used to make gametes (sex cells)
Crossing overProcess in which homologous chromosomes trade parts
InterphasePhase of the cell cycle where the cell grows and makes a copy of its DNA
Homologous chromosomesSet of chromosomes (one from each parent), that are very similar to one another and have the same size/shape
Sister chromatidsTwo halves of a duplicated chromosome
Diploid (2n)Cell that contains two sets of homologous chromosomes
Haploid (n)Cell that contains only a single set of genes

Meiosis

The purpose of meiosis is to produce gametes, or sex cells. During meiosis, four daughter cells are produced, each of which are haploid (containing half as many chromosomes as the parent cell).

Stages of meiosis

Meiosis contains two separate cell divisions, meaning that one parent cell can produce four gametes (eggs in females, sperm in males). In each round of division, cells go through four stages: prophase, metaphase, anaphase, and telophase.
Before entering meiosis I, a cell must first go through interphase. This is the same interphase that occurs before mitosis. The cell grows, copies its chromosomes and prepares for division during the G1_1​​ phase, S phase, and G2_2 phase of interphase.

Meiosis I

Meiosis I is the first round of cell division, in which the goal is to separate homologous pairs.

Meiosis II

The second round of cell division is meiosis II, in which the goal is to separate sister chromatids.

Common mistakes and misconceptions

  • Interphase is not part of meiosis. Although a cell needs to undergo interphase before entering meiosis, interphase is technically not part of meiosis.
  • Crossing over occurs only during prophase I. The complex that temporarily forms between homologous chromosomes is only present in prophase I, making this the only opportunity the cell has to move DNA segments between the homologous pair.
  • Meiosis does not occur in all cells. Meiosis only occurs in reproductive cells, as the goal is to create haploid gametes that will be used in fertilization.
  • Meiosis is important to, but not the same as, sexual reproduction. Meiosis is necessary for sexual reproduction to occur, as it results in the formation of gametes (sperm and eggs). However, sexual reproduction includes fertilization (the fusion between gametes), which is not part of the meiotic process.
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