1. Cell Division
Mitosis and Meiosis

2. Recall A Few Main Things
All new cells come from existing cells
DNA is stored in the nucleus of cells in eukaryotes

3. Chromosomes A chromosome is a single, very long, strand of DNA
Each chromosome contains many thousands of genes

4. Diploidy Each species has a set # of chromosomes
We also have 2 versions of each chromosome (called homologous chromosomes)
I.e. humans have 23 sets of chromosomes, or 46 total

5. Types of Cell Division
Usually when we make new cells, we want them to be identical to existing cells
i.e. make new skin cells from existing ones
The new cell is completely identical

6. Mitosis Cell division that creates identical daughter cells
So the new cell has the exact same chromosomes as the original cell

7. The Extent of Mitosis
Almost every single cell in our body is made from mitosis
Exceptions: the first cell, sperm/egg cells
When we grow new skin, new hair, new muscles – all of that is mitosis
So every cell in our body has the exact same set of chromosomes

8. Sperm/Egg You pass on half your genes to offspring
You must make a gamete (sperm or egg cell) with half of your chromosomes
Each gamete randomly receives 1 of the 2 versions of each chromosome

9. Meiosis Each parent cell produces 4 daughter cells
Each daughter cell has 1 set of chromosomes (half of the parent’s chromosomes)
(is haploid)

10. # of Possible Gametes
There are 223 possible chromosome combinations to make a gamete
=8,388,608 possibilities
So you are 1 out of 8,388,6082 possibilities
You are quite literally 1 in a trillion (1 of 70,368,744,200,000 possible combinations of your parents)

11. Mitosis vs. Meiosis Mitosis Meiosis
Identical offspring (same set of chromosomes)
2 daughter cells
Creates all body cells
Produces diploid cells
Offspring have half as many chromosomes
4 daughter cells
Creates sperm/egg
Produces haploid cells
Mitosis vs. Meiosis

12. What’s the Point?
Meiosis allows us to have offspring that are different and have a unique combination of genes
This increases diversity in the population
Increased diversity means increased ability for the species to survive and adapt to new situations