BSC 2010L

Prokaryotic Cells  Divide by binary fission Produces “clones” Only have to worry about 1 circular chromosome Eukaryotic cells have many linear chromosomes, requires organization, therefore mitosis is needed

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 G 1 is where the cell performs it’s “normal” cell functions (may be days or years depending on cell type)

 Humans 46 chromosomes 23 homologous pairs ○ Each pair: 1 came from mom, 1 came from dad

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!!!!!!

Meiosis  The purpose: haploid (1n) sperm haploid (1n) ovum diploid (2n) zygote

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?

Meiosis  At the beginning of meiosis, homologous chromosomes find each other This is where crossing over occurs

Gametogenesis in Animals  Spermatogenesis  Oogenesis  Notice how there is 1 egg

What is Non-disjunction?

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  Identify stages – answers on next slide

Onion Root Tip - mitosis

Onion Root Tip - Mitosis  Identify stages

Onion Root Tip - Mitosis

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

Lily meiosis in the anther (production of pollen)

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 20mei%20modelsHTML/index.htm 20mei%20modelsHTML/index.htm  Use bead models to demonstrate mitosis and meiosis