Meiosis involves two cell divisions that result in four haploid cells from one original diploid cell. During the first meiotic division, homologous chromosomes pair up and may exchange genetic material through crossing over. The second meiotic division separates the chromatids so that each of the four resulting haploid cells receives one chromosome from each homologous pair. Gene linkage occurs when genes located near each other on the same chromosome tend to be inherited together.

1. Meiosis and Gene Linkage

2. PMAT

3. Chromosome NumberDiploidHomologousHaploid

4. Phases of MeiosisMeiosisBy the end of meiosis II, the diploid cell that entered meiosis has become four haploid cells

5. What Happens When It Goes Wrong?

6. Meiosis I: ProphaseTetradO Crossing Over

7. Meiosis I: MetaphaseSpindle fibers attach to the chromosomes

8. Meiosis I: AnaphaseThe fibers pull the homologous chromosomes toward opposite ends of the cell

9. Meiosis I: Telophase and CytokinesisNuclear membranes form. The cell separates into two cellsThese two cells enter Meiosis II

10. Meiosis II: ProphaseUnlike the first division, neither cell goes through a round of chromosome replication before entering meiosis IIEach of the cell’s chromosomes has 2 chromatids

11. Meiosis II: MetaphaseChromosomes line up in the center of each cell

12. Meiosis II: AnaphaseThe paired chromatids separate and move toward opposite ends of the cell

13. Meiosis II: Telophase and CytokinesisEach cell separates into two cells - meaning four haploid cells all together

15. Gamete FormationIn male animals, meiosis produces four haploid sperm cells However, the cell divisions at the end of meiosis are uneven in females, so that only a single cell receives most of the cytoplasm

16. Mitosis vs. Meiosis

17. Gene LinkageIt is the chromosomes that assort independently, not the individual genesMendel did not discover gene linkage (Morgan did)

18. Gene Maps