1. Meiosis – a form of cell division that halves the number of chromosomes when forming reproductive cells, such as gametes (egg & sperm cells)

2. Stages of Meiosis: *Before meiosis begins, DNA in
the original cell is replicated.
In meiosis, the cell undergoes two
cell divisions: Meiosis I and Meiosis II.
The cell then goes through two cell
divisions: Meiosis I and Meiosis II.

3. Meiosis I: Meiosis I: Homologous chromosomes
separate; This stage consists
of prophase I, metaphase I,
anaphase I, and telophase I.

4. Meiosis I 2n
Crossing
Over
Independent
Assortment n

5. Crossing Over
Occurs when portions of a chromatid on one homologous chromosome is broken and exchanged with the corresponding chromatid portion of the other homologous chromosome.

6. Meiosis II: Meiosis II: The 2 chromatids (referred to
as sister chromatids) separate;
This stage consists of prophase
II, metaphase II, anaphase II,
and telophase II.

7. * All 4 cells are genetically different!!
Meiosis II n
* All 4 cells are genetically different!! n

8. 2n
Meiosis: -reduces the number of chromosomes by half to form gamete cells
centromere n n

9. Three Mechanisms that Contribute to Genetic Variation:
1. crossing over – when portions of a chromatid on one homologous chromosome is broken and exchanged with the corresponding chromatid portion of the other homologous chromosome
2. independent assortment – the random distribution of homologous chromosomes during meiosis
3. random fertilization – the random joining of 2 gametes

10. Importance of Genetic Variation:
It allows organisms to change so they can better adapt to the changing environment !