Mitosis and Meiosis BSC 1005L

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 #)

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)

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!!!!!!

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

Onion Root Tip - mitosis

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?

Gametogenesis in Animals Spermatogenesis Oogenesis Notice how there is 1 egg

Onion Root Tip - Mitosis

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

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

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 http://faculty.irsc.edu/DEPT/BiologicalSciences/mit%20mei%20modelsHTML/index.htm Use bead models to demonstrate mitosis and meiosis