2. The Basics Within the nucleus are chromosomes Chromosomes occur in pairs  one from mother, one from father  each member of the pair is basically identical  homologous chromosomes

3. most of an organism's cells are diploid (2n) produced through mitosis somatic cells or body cells (not sex cells)

4. an organism's sex cells are haploid (n) contain ½ the number of chromosomes produced through meiosis germ cells, gametes (egg and sperm)

5. The Cell Cycle

6. The lifespan of a cell growth, replication, and division (reproduction) occur Divided into 2 basic phases: Interphase (cell doing job) G1- growth of cell, doubles organelles, accumulates materials S- DNA is copied (synthesized), chromatids form G2- proteins that assist in cell division formed, mitotic spindle Mitosis (cell division)

7. Not all cells divide (nerve, muscle cells), stay in stage Go Checkpoints are found at the end of G1 and G2 that allow the cell to progress Cyclins- proteins that allow cell division to progress p53 controls checkpoint and will stop cell division in damaged cells

8. All cancer cells have multiple mutations Mutations in checkpoints (esp. p53) allow cell to divide when damaged Apoptosis (preprogrammed cell death) stops, telomeres (chromosome tips) do not shorten, or proteins bind that prevent checkpoint from stopping cell division All can lead to cancer.

11. Mitosis is 1:2 cell division Parent cells divide to form daughter cells which are identical to parent cells Composed of 4 phases  Prophase  Metaphase  Anaphase  Telophase

12.  early prophase  nucleolus and nuclear envelope disappear  centrioles migrate to opposite poles (animal cells)  chromatin thickens into full chromosomes

13.  late prophase  asters form and spindle fibers become visible  kinetochore (spindle fibers) attach to centromeres

14.  chromosomes line up along equatorial plane by their centromeres  they are perpendicular to each pole

15.  centromeres of each chromosome divide in half  sister chromatids detach  sister chromatids move toward opposite poles as spindle fibers pull them

16.  spindle fibers disappear  centrioles return to normal position  nucleolus and nuclear envelope reform  chromosomes unravel back into chromatin

17.  division of the cytoplasm  plasma membrane furrows and cleaves (divides in ½)  2 identical daughter cells are produced  in plants, the new cell wall begins as a cell plate  does not have to occur in all cells of all organisms ie. Multi-nucleated tissue

18. primary means of asexual reproduction (binary fission, budding) all tissue growth takes place through mitosis replacement of old, damaged, or malfunctioning cells repair of damaged tissue Allows cell specialization to occur

20. Meiosis is special kind of cell division it occurs only in certain reproductive organs/cells cells undergoing meiosis are called germ cells gametes (egg or sperm) result gametes are haploid gametes are not genetically identical to the parent cell meiosis is a 1:4 cell division one diploid cell divides to produce 4 non- identical haploid cells

21. produces haploid gametes ensures that offspring receive a full set of chromosomes introduces genetic variability into the gametes and offspring

22. more complicated than mitosis interphase with G1, S, and G2 is the same M phase is now meiosis it is divided into 2 sets of cell divisions: meiosis I and II reduction division

23.  nuclear envelope and nucleolus disappear  centrioles migrate to opposite poles  spindle fibers appear as asters

24.  synapsis  homologous chromosomes physically paired  homologues  tetrads (bivalents)  crossing over (crossover)  non-sister chromatids exchange segments of themselves with each other  chiasmata  Allow for more variation

25.  tetrads line up along the equatorial plane  homologous chromosomes in each tetrad line up on random sides of each other  independent assortment  promotes genetic diversity  spindle fibers attach to centromeres

26.  homologous chromosomes separate and move to opposite poles

27.  nuclear envelope and nucleolus reform  centrioles return to normal position  spindle fibers disappear

28.  cell cleaves into two daughter cells  have 2 non-identical, diploid cells at the end of meiosis I

29.  essentially the same as mitosis  each haploid daughter cell divides again  independent separation of sister chromatids  have 4 non-identical, haploid gametes at the end of meiosis II  these 4 came from one diploid germ cell