1. Chapter 11 and 12 Mitosis and Meiosis
One cell division
Produces 2 identical cells
Used for growth, tissue repair, and asexual reproduction
Meiosis
Two cell divisions
DNA replicates once
Produces 4 haploid cells
Provides variation
Primary purpose: Gamete production

2. The Cell Cycle
The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell.
1. Interphase consists of three phases:
growth
synthesis of DNA
preparation for mitosis
2. The cell cycle is directed by internal controls
or checkpoints.
Internal and external signals provide stop-and-go signs at the checkpoints.

3. Regulation of Cell Cycle
Mitosis-promoting factor (MPF)
Action of platelet-derived growth factor (PDGF)
Cancer results from disruptions in cell cycle control
Cyclins and cyclin-dependent kinases control the cell cycle.

4. More Mitosis Facts
Mitosis alternates with interphase in the cell cycle.
When a cell specializes, it often enters into a stage where it no longer divides, but it can reenter the cell cycle when given appropriate cues.
Non-dividing cells may exit the cell cycle; or hold at a particular stage in the cell cycle.

5. Mitosis passes a complete genome from the parent cell to daughter cells.
1. Mitosis occurs after DNA replication.
2. Mitosis followed by cytokinesis produces two genetically identical daughter cells.
3. Mitosis plays a role in growth, repair, and asexual reproduction
4. Mitosis is a continuous process with observable structural features along the mitotic process

6. I) Eukaryotic Chromosomes
Form highly condensed pairs of chromosomes
Homologous Chromosomes – chromosomes with the same genes, same size, same appearance
Genes are located at the same location (locus)
b) Homologous chromosomes
may contain different forms of the
same genes (dominant or
recessive forms)
These forms of genes are called ALLELES

7. B) Sex Chromosomes and Autosomes 1) Sex chromosomes (X or y) contain genes that determine gender 2) Autosomes contain genes that determine traits other than gender 3) Humans cells contain 44 autosomes and 2 sex chromosomes

9. C) Haploid vs. Diploid vs. Polyploid
Haploid – cells with ½ normal number of chromosomes
Gametes (sex cells)
“n” number In humans n=23
Diploid – cells with the normal number of chromosomes
Body cells (somatic cells)
“2n” number In humans 2n = 46
Polyploid – cells with more than the normal number
of chromosomes
Cells can have an extra set or more
3n, 4n, 6n, 8n

10. The Cell Cycle

11. I) Three Parts of the Cell Cycle
Interphase – cell grows and performs its usual functions
G1 (Gap 1) – growth and metabolism
S (Synthesis) – DNA Replication begins
G2 (Gap 2) – DNA replication complete
Mitosis – division of genetic material
Four phase process (awesome animation!)
Form two new nuclei
Cytokinesis – division of the cytoplasm to form two new cells
Cell Plate (in plants) forms a new cell wall
Cleavage Furrow (in non-plants) pinches to split cells
Syncytium – cell with 2 nuclei when cytokinesis does not occur (syncytia is plural form)

14. II) When do Cells Divide?
When cell size becomes too large and surface-area-to-volume ratio decreases
Some cells divide once a day, once a week, once a lifetime
Nerve cells, red blood cells, muscle cells divide until the differentiate

15. III) Control of Cell Division
Growth Factors – proteins that bind to plasma membrane receptors and trigger mitosis (can be hormones)
Hormones – Steroid hormones bind to DNA via nuclear hormone receptor proteins
Cyclin – protein that activates enzymes to initiate replication
Stimulates transcription and replication factors

16. Important Proteins in the Cell Cycle
Ras Cyclin – verifies cell is proper size
P53 – Tumor Suppressor Protein checks DNA for damage before replication
Stops cell cycle if DNA is damaged
Many cancers associated with a defective p53 gene
MAD1 – Verifies spindles attach to kinetochore

18. IV) Cancer Cells that grow abnormally
Three key features of cancerous cells
Rapid cell division
Undifferentiated
Angiogenesis – signal blood vessel growth
Genetic Causes
Mutations in genes
Tumor Suppressor Genes
normally inhibit cell growth by suppressing mitosis
Proto-oncogenes – genes that signal cell growth to occur (code for growth factors, hormones, RNAi)

19. Chapter 12: Meiosis
Meiosis (Reduction Division) – Gametogenesis – gamete formation
Meiosis, followed by fertilization ensures genetic diversity in sexually reproducing organisms.
Two Cell Divisions
Meiosis I
DNA replication
Synapsis and Tetrad Formation
Cross overs of chromosomes
Two cells produced
Meiosis II
NO replication
DNA divides into 4 cells
Produce haploid cells

20. II) Purpose of Meiosis A) Adaptation for the following: 1
II) Purpose of Meiosis A) Adaptation for the following: 1. Maintain consistent chromosome numbers for sexual reproduction 2. Provide variation through genetic recombination a) form new gene combinations through shuffling chromosomes and crossing- over

21. III) Problems with Meiosis A) Non-Disjunction
1. Chromosomes fail to properly separate
after meiosis I
2. Polyploidy results from non-disjunction
3. Polyploid Conditions
a) Down Syndrome – trisomy 21
b) Patau Syndrome – trisomy 13
c) Edwards Syndrome – trisomy 18
d) Klinefelter’s Syndrome – XXY
e) Supermale - XYY