Bio102: Introduction to Cell Biology and Genetics
Cell Cycle and Cell Division
Key Terms:
Interphase
Mitosis
G1 and G2
S phase
M phase
Checkpoints
G0
Sister chromatid
Centromere
Telomere
Spindle
Centrosome
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Metaphase plate
Meiosis
Homologous pair
Crossing over
Key Questions:
 What happens in each of the stages of mitosis?
 Which cells of the body undergo mitosis? Which undergo meiosis?
 Why are two divisions needed in meiosis?
 What key event occurs in prophase of meiosis I that did not occur in mitosis?
 Why is it more difficult to divide up the genetic material between the daughter cells than to
divide up the cytoplasmic enzymes, ribosomes, mitochondria, etc.?
 Why is it important that the two sister chromatids remain attached after DNA replication is
complete? At what point in meiosis is a haploid cell produced?
Lecture Outline:
Mitosis (M phase) is when chromosomes become visible and get separated to the daughter cells
the rest of the time is Interphase (composed of G1, S and G2 phases)
DNA is synthesized in S phase only
during duplication, the chromosome goes from having one chromatid to two chromatids
still just one single chromosome
sister chromatids are connected at the centromere
Nondividing cells are in G0. May enter G1 only if appropriate external signals are provided
Checkpoints in late G1, late G2 and M phases
M phase can be separated to Prophase, Prometaphase, Metaphase, Anaphase, Telophase&Cytokinesis
Prophase: DNA condenses and become visible to the microscope. Spindle forms
Prometaphase: Nuclear membrane breaks down. Centrosomes on chromosomes attach to spindle
Metaphase: chromosomes align in the middle of the cell
Anaphase: sister chromatids separate and begin moving to the poles
Telophase and cytokinesis: more movement of chromatids
nuclear membrane re-forms. chromosomes de-condense
cells splits down the middle (cytokinesis)
result of mitosis is two identical, diploid cells
Meiosis is used to create haploid gametes
replication still happens, followed by two cell divisions (Meiosis I and Meiosis II)
very similar to mitosis, except for the arrangement of the chromosomes in Metaphase I
homologous pairs of chromosomes pair up together
Meiosis I separates homologous pairs. Meiosis II separates sister chromatids