1. MEIOSIS
Meiosis is the type of cell division by which germ cells (egg and sperm) are produced.
Meiosis involves a reduction in the amount of genetic material.
Meiosis comprises two successive nuclear divisions with only one round of DNA replication.

2. MEIOSIS Meiosis I (First division of meiosis)
Prophase 1: Each chromosome seeks out its corresponding homologous chromosome to form a special structure called a tetrad (which contains 4 chromatids).
At this point homologous chromosomes may exchange portions of their chromatids in a process called crossing-over.
This results in new gene combinations.

3. MEIOSIS

4. MEIOSIS
Metaphase 1: Homologous chromosomes align at the equatorial plate.
Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

5. MEIOSIS Meiosis II (Second division of meiosis): Gamete formation
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes align at the equatorial plate.

6. MEIOSIS
Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

7. MEIOSIS

8. MEIOSIS
One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.
In females the cell division at the end of meiosis I & meiosis II are uneven and therefore the egg receives most of the cytoplasm.

9. MEIOSIS
The other 3 cells are called polar bodies and usually do not participate in reproduction.
In animals the female gamete is called an egg and the male gamete is called sperm.

10. MEIOSIS

11. MEIOSIS and GENETICS
Chromosomes pair and separate during meiosis in a manner that Mendel would have predicted.
During anaphase 1 of meiosis, homologous chromosomes separate in a way that also segregates the alleles located on the chromosomes.

12. MEIOSIS and GENETICS This agrees with Mendel’s law of segregation.
Also, the random separation of chromosomes during the first meiotic division means that the chromosomes assort independently,
agreeing with Mendel’s law of independent assortment.

13. Comparing Meiosis and Mitosis
Meiosis Mitosis
2 cell divisions cell division
Result: 4 haploid cells (N) Result: 2 diploid cells (2N)
Cells are genetically Cells are genetically
different. the same.