Meiosis Meiosis lecture notes Timed quiz Micrographs Mitosis / meiosis comparison
Interphase As with mitosis, DNA replication takes place during interphase before meiosis begins. Centrioles Nucleus
Prophase I Chromosomes condense Centrioles duplicate and move towards poles Micrograph
Prophase I Chromosomes condense Centrioles duplicate and move towards poles
Prophase I Chromosomes condense Centrioles duplicate and move towards poles Nuclear membrane breaks down
Prophase I Nuclear membrane breaks down Micrograph
Prophase I Spindle begins to form Homologous chromosomes pair up (synapsis) forming bivalents. Crossing over may occur between chromatids Detail of crossing over
Metaphase I Spindle begins to form Chromosomes line up on equator of cell in homologous pairs (bivalents)
Metaphase I Chromosomes line up on equator of cell in homologous pairs (bivalents) Micrograph
Anaphase I Chromosomes pulled to opposite ends of the cell by spindle fibres
Anaphase I Chromosomes pulled to opposite ends of the cell by spindle fibres Micrograph
Telophase I Nuclear membrane may reform (Chromosomes may recondense) Micrograph
Telophase I In some organisms, cytokinesis takes place at the end of telophase I
Prophase II In some organisms, cytokinesis takes place at the end of telophase I
Prophase II Centrioles replicate Nuclear membrane breaks down
Metaphase II Centrioles move to poles of cells Spindle forms; chromosomes line up on equator Micrograph
Anaphase II Centromeres divide, and chromatids are moved to opposite ends of the cells by spindle fibres Micrograph
Telophase II
Telophase II Nuclear membranes reform Cytokinesis follows
Telophase II Nuclear membranes reform Cytokinesis follows
4 haploid cells Telophase II Nuclear membranes reform Cytokinesis follows 4 haploid cells Micrograph
Meiosis animation Try to identify the different phases in this animation of meiosis
Random assortment If a cell with two pairs of chromosomes undergoes meiosis there are four possible combinations of chromosomes in the gametes produced.
Random assortment How many possible combinations of chromosomes are there in human gametes with 23 pairs of chromosomes? 223 = 8388608
DNA replicates during interphase Crossing over
DNA replicates during interphase Crossing over
Crossing over DNA replicates during interphase During prophase I chromatids break and reconnect to a different chromatid in the bivalent Crossing over
Crossing over DNA replicates during interphase During prophase I chromatids break and reconnect to a different chromatid in the bivalent This results in different combinations of alleles on the chromosomes Crossing over
Crossing over DNA replicates during interphase During prophase I chromatids break and reconnect to a different chromatid in the bivalent This results in different combinations of alleles on the chromosomes Crossing over
Chiasmata Crossing over The point on a chromosome where crossing over takes place is described as a chiasma (plural: chiasmata). One or more chiasmata may form anywhere along the length of the two chromosomes involved in crossing over. Chiasmata Back to metaphase I
Meiosis overview
There are eight questions. Meiosis quiz You will need a pen and paper. You have ten seconds to answer each question. Answers are shown at the end. There are eight questions. Start
1. Which stage of meiosis is this?
2. Which of these diagrams shows anaphase I of meiosis? B C D
3. At which stage of meiosis does crossing over happen? Telophase II Anaphase I Metaphase I Metaphase II Prophase I
4. Which stage of meiosis is this?
5. Which of these micrographs shows late anaphase II? B C D
6. Crossing over results in new combinations of: Alleles Chromosomes Chromatids Bivalents
7. Which of these stages of meiosis is telophase II? B C D
8. Which stage of meiosis is shown on this micrograph?
View questions again Answers
1. Which stage of meiosis is this? Metaphase II
2. Which of these diagrams shows anaphase I of meiosis? B C D
3. At which stage of meiosis does crossing over happen? Telophase II Anaphase I Metaphase I Metaphase II Prophase I
4. Which stage of meiosis is this? Telophase I
5. Which of these micrographs shows late anaphase II? B C D
6. Crossing over results in new combinations of: Alleles Chromosomes Chromatids Bivalents
7. Which of these stages of meiosis is telophase II? B C D
8. Which stage of meiosis is shown on this micrograph? Metaphase II
Meiosis Meiosis lecture notes Timed quiz Micrographs Mitosis / meiosis comparison
Prophase I Return to notes
Prophase I Return to notes
Metaphase I Return to notes
Anaphase I Return to notes
Telophase I Return to notes
Metaphase II Return to notes
Anaphase II Return to notes
Telophase I Return to notes