1. Mitosis and Meiosis
BSC 1005L

2. Why do eukaryotic cells divide?
Growth and Repair
Mitosis
Produces 2 identical cells with same # chromosomes (diploid #)
Reproduction
Meiosis
Produces cells with ½ chromosomes (haploid #)

3. Eukaryotic Cell Cycle 2 main phases Mitosis Interphase
Long period between cell division
Some cells stay in interphase indefinitely
G1 is where the cell performs it’s “normal”
cell functions (may be days or years depending
on cell type)

4. Ploidy # of sets of chromosomes in a cell Haploid (n) – one set
Egg and sperm
Diploid (2n) – two sets
All of our other cells
Example:
In humans,
Haploid # = 23
Diploid # = 46
These #’s will vary depending on the species!!!!!!

6. Onion Root Tip – Mitosis Area of lots of cells undergoing mitosis in various stages
What you will see at 40x –
Have to magnify further to
See individual cells

7. Onion Root Tip - mitosis

9. Meiosis Humans have 46 chromosomes, 23 homologous pairs
What is homologous?
During Meiosis, it is VERY important that one of EACH homologous pair ends up in the gamete (sperm or egg)
Why?

12. Gametogenesis in Animals
Spermatogenesis
Oogenesis
Notice how there is 1 egg

13. Onion Root Tip - Mitosis

14. Whitefish blastula - Mitosis
What you will see at 40x, each circle is a
Cross-section of the blastula, focus in
to see individual cells
Focus in on the individual cells
This is an example of anaphase

16. Differences between mitosis and meiosis
Mitosis is one division, meiosis is two (meiosis I and II)
Mitosis results in 2 identical daughter cells, meiosis results in 4 haploid cells
Homologous chromosomes find each other before meiosis I
Crossing over occurs
Mitosis is for growth and repair, meiosis is for reproduction

17. In this lab: Observe microscope slides of mitosis and meiosis
Look at models of mitosis and meiosis
Tutorials of these models can be found on the Biology Department Laboratory resources page
Use bead models to demonstrate mitosis and meiosis