Major Concepts to Review for A.P. Exam

Cell Reproduction


DNA is packaged in the nucleus

  1. histone proteins necessary for first coiling = nucleosomes (looks like beads on a string)
  2. three or four additional levels of coiling produce the thick short structure called a chromosome, visible under the light microscope (only the most powerful electron microscopes can "see" nucleosomes
  3. Thickness changes from 10 nanometer nucleosome to a metaphase chromosome = 1000 nm (an increase in thickness of 100)

The Cell Cycle



  • Prophase - most events including DNA condenses, nuclear membrane is disassembled, spindle apparatus is assembled (in animals centrioles divide and migrate to opposite poles.
  • Metaphase - chromosomes line up due to multiple microtubules connected at the centromere/kinetochore region
  • Anaphase - centromere splits and daughter chromatids are toughed apart moving to opposite poles
  • Telophase - generally opposite of prophase
  • Cytokinesis - 2 cells half the size of the original cell emerge as a cleavage furrow (animals) pinches in or a cell plate forms midway between the poles of the old cell (plants)


Mitosis - Advantages

growth by easily adding to the number of cells

repair - would healing

maintenance of cell count by replacing old cells (red and white blood cells for example)



  • converts diploid cell into haploid condition
  • involves 2 nuclear divisions: meiosis I and Meiosis II
  • meiosis I reduces chromosome # in half (the reduction division). Homologous chromosomes are separated in anaphase I. Otherwise steps similar to mitosis.
  • meiosis I involves crossing over of homologous chromosomes in prophase I - shuffling of genes increases variation in the next generation (natural genetic recombination)
  • meiosis II identical to mitosis but results in 4 cells
  • meiosis differs between males and females.

Meiosis - purpose

necessary for sexual reproduction because 2 haploid cells will unite to from a diploid zygote

meiosis results in haploid cells with greater variety because of crossing over events in prophase I - some variations may be advantageous.

Additional Information may be found at: