Topic 5 Cell Division: Mitosis

Question 1

• Process required for life

- Occurs in two steps: nuclear division followed by cytokinesis

Answer 1

Cell Division

Question 2

• Two copies of every chromosome
• Humans have 46 chromosomes (23 homologous pairs)
• One chromosome is made up of two sister chromatids (humans= 92 chromatids)

Answer 2

Diploid Cells

Question 3

• Cell division in all body cells except germ/reproductive (meiosis)
• Occurs in somatic cells

Answer 3

Mitosis

Question 4

• Microtubule organizing centers
• Key players in cell division
• A pair lay outside the nucleus in animal cells
• Each contains a pair of centrioles

Answer 4

Centromeres

Question 5

• In plants

- Not composed of centrioles

Answer 5

Centrosomes

Question 6

• Nucleus disassembles, nucleolus disappears, chromatin condenses into chromosomes, nuclear envelope breaks down
• Mitotic spindle forms and microtubules (composed of tubulin) start connecting to kinetochores

Answer 6

Step 1: Prophase

Question 7

• Chromosomes line up along center of cell and spindle fibers attach to kinetochore of each chromatid. Chromosome becomes chromatid during anaphase. Karyotyping performed during this phase

Answer 7

Step 2: Metaphase

Question 8

• Microtubules shorten and each chromosome is pulled apart into two chromatids. Separated = chromosome making the chromosome number double. Microtubules pull chromosomes to opposite poles (disjunction). Result: each pole has complete set of chromosomes. This is shortest step

Answer 8

Step 3: Anaphase

Question 9

• Nuclear division occurs
• Nuclear envelope develops
• Chromosomes unravel = chromatin
• Nucleoli reappear

Answer 9

Step 4: Telophase

Question 10

• Begins during end of anaphase
• Involves division of cytoplasm forming two cells
  a. Cleavage furrow forms in animal cells. Actin and myosin microfilaments shorten. Plasma membrane pulled to center.
  b. In plant cells vesicles from Golgi migrate and fuse forming cell plate. Plate grows and merges with plasma membrane eventually separating two new cells
• Cell plate doesn’t separate cells, the middle lamella (cell plate) cements adjacent cells together

Answer 10

Step 5: Cytokinesis

Question 11

• Joining of gametes is random, but some sperm cells contain genetic material that gives them a competitive advantage – so they all aren’t equally competitive
• Mitosis does not result in any genetic variation
• If you are seeing chromosomes, that means the chromatin has condensed already, do you’re actually seeing mitosis. Therefore, if you’re asked to determine the number of chromatids, assume they’ve already been doubled in this situation
• At anaphase of mitosis, there would be a total of 92 chromosomes (92 chromatids). If a cell starts with 46 chromosomes and we pull apart the sister chromatids, each one if now a complete chromosome, and we count centromeres
  a. At anaphase I, there would be a total of 46 chromosomes if a cell has 46 chromosomes to start with. This is because 23 chromosomes (since haploid) are pulled to each pole via independent assortment, and no chromatids are separated in anaphase I.

Answer 11

Additional Notes about Cell Division