Mitosis/Meiosis

Question 1

What is chromosome segregation?

Answer 1

Process of distributing a copy of each chromosome to each daughter cell (during mitosis)

Question 2

What is a centrosome? What does it do?

Answer 2

Aka microtubule organizing center (MTOC)

• form foci with microtubules radiating out during PROPHASE of mitosis
• gradually move to poles of cell

Question 3

What are types of atypical mitosis?

Answer 3

• Multipolar division
• Bridge formation
• No cytokinesis
• Non-disjunction
• Endoreduplication (endomitosis)

Question 4

Which types of atypical mitosis cause abnormal chromosome #’s?

Answer 4

• multipolar division
• non-disjunction
• -> polyploid can occur from endomitosis

Question 5

What is a H3P?

Answer 5

Phosphorylated H3 histone, needed for chromosome condensation

Question 6

What is PCNA?

Answer 6

=Proliferating cell nuclear antigen

- cofactor for DNA polymerase, expressed in S phase

Question 7

What is Ki67 antigen?

Answer 7

Associated with cell proliferation

- thus NOT expressed in G0

Question 8

What are methods to study the cell cycle?

Answer 8

• Microscopy:
  - division markers (PCNA, H3P, Ki67 antigen)
  - detecting S phase
  - Fucci (fluoresc. ubiqtnd cell cycle indicator)
  - mitotic index (MI)
  (MI= mitotic cells/total cells x 100)
• Flow cytometry

Question 9

What are homologous chromosomes?

Answer 9

They are chromosomes that contain DNA that code for the same gene
- BUT, homologous chromosomes are NOT replicas of each other (sister chromatids are exact replicas)

Question 10

List steps in Prophase I, and significance for each one.

Answer 10

1) Leptotene: chromosome condenses
2) Zygotene: synapsis begins, synaptonemal complex begins to form, holds chromosomes together (essential for recombination)
3) Pachytene: synapsis complete, forms bivalent (tetrad)
- CROSSING over occurs!!!
4) Diplotene: synaptonemal complex starts to break down, bivalents start to separate, held together by chiasmata
5) Diakinesis: chromosomes reach max. condensation

Question 11

What are pseudoautosomal regions?

Answer 11

Pseudoautosomal regions (PAR) 1 and 2 are on the X and Y chromosomes. They pair and recombine during meiosis

Question 12

What causes aneuploidy?

Answer 12

Meiotic non-disjunctions
(most frequent in oogenesis)
-sex chromosome non-disj. more common in spermatogenesis