The document discusses the processes of cell division through mitosis and meiosis. Mitosis results in identical body cells and is used for cell replacement and growth in multicellular organisms. Meiosis results in genetically unique gametes and is used in sexual reproduction. It also describes the cell cycle phases of interphase, mitosis/meiosis, and cytokinesis. Key aspects of each phase are outlined like DNA replication in S phase and nuclear and cell division. Chromosomes, sister chromatids, and the stages of mitosis are defined. Today's lab activities on observing mitosis in cells are listed.

1. Cell division: Mitosis
• Necessary process
• Results in identical cells
• Simple, single celled organisms use for
reproduction
• More advanced, multi-celled organisms
use for cell replacement and growth
– Occurs in somatic cells, body cells
– Diploid: two copies of each chromosome

2. Cell division: Meiosis
• Reductive division
• Results in genetically unique cells
• Used by sexual multicellular organisms
to produce gametes
– Haploid: one copy of each chromosome
– Occurs in specialized germ cells

3. Chromosome
• Single, long piece of DNA wrapped
around proteins
• The number of chromosomes differs
between organisms

4. Phases of the Cell Cycle
• Interphase
– Time of normal cell
activities
– Longest phase
– DNA replication occurs
• Mitosis/Meiosis
– Time of nuclear division
• Cytokinesis
– Time of cytoplasm division

5. Duplicated chromosome:
Sister Chromatids
• Two copies remain attached at the
centromere
• Each copy is a chromatid
• Together they make up one
duplicated chromosome
• Split during nuclear
division

6. Interphase
• Longest part of cycle
• Three stages
– G1: cell grows and functions normally
– S: DNA is copied
– G2: cell prepares to divide

8. Cytokinesis
• Division of the
cytoplasm
• Animal cells:
cleavage furrow
• Plant cells: cell
plate formation

9. Today’s Mitosis
1. Look at Mitosis models
2. Observe whitefish blastula
cells under microscope
(animal cell mitosis)
3. Sketch each stage of
mitosis observed in onion
root tip cells (plant cell
mitosis)

10. Today’s Mitosis
1. Look at Mitosis models
2. Observe whitefish blastula
cells under microscope
(animal cell mitosis)
3. Sketch each stage of
mitosis observed in onion
root tip cells (plant cell
mitosis)