Class Notes: Meiosis
Activity 1: Use the cut-out chromosomes from the Mitosis worksheet.
A. Use the chromosomes to take your cell from G1 to Metaphase 1. How does Metaphase 1 look
different from Metaphase in mitosis?
B. How would your arrange the chromosomes at Metaphase one to have at least one haploid daughter
cell with “genes” of all lower-case letters?
C. Show your neighbor the difference between a kinetochore and a centromere. Which are there more
of?
D. 3. Can you have a gamete that has a chromosome “h R”?
E. Create a cell in which 2n = 4 in G1.
Activity Wrapup:
Mitosis, in contrast to Meiosis:
A. Produces gametes
B. Requires a previous S phase
C. Is seen in gut epithelial cells
D. Has crossing over before anaphase
E. Results in diploid cells
Activity 2: Older oocytes are more prone to aneuploidy
(http://www.sciencedirect.com/science/article/pii/S0960982210008171)
Hypothesis: older oocytes may lose cohesion between sister chromatids,
increasing the likelihood of aneuploidy:
This experiment examined oocytes in both young (3 months) and older (15-17 months) mice.
Look at “Figure A” on the slide, and look at the results below.
1. In M1, should sister kinetochores be close together or far apart?
2. What happens in older mice?
In order to explain the loss of cohesion, researchers measured levels of a protein called REC8. Look at
“Figure B” on the slide, and the results below.
3. Where is REC8 found in the cell?
4. What is the message of these figures?
Activity Wrapup:
Determine which of the following are true:
A. Chromosomes in M1 are in tetrads
B. M1 in oocytes can last for more than 20 years in humans
C. An error in Anaphase 1 can retain homologous chromosomes in a daughter cell
D. Anaphase 1normally separates sister kinetochores
E. Younger mice have sister kinetochores that are farther apart
F. Older mice have more cohesion in the centromere
G. Loss of a cohesion protein is associated with reduced aneuploidy
Fill in the table below for human cells: 2n = 46
Stage
Cells in G1
How many
chromosomes?
Chromosomes look
like:
How many sister
chromatids?
46
Ploidy?
2n or n
0
2n
S phase / Chromosome duplication
In G2
Mitosis
Daughter cells
after mitosis
Meiosis
Daughter cells
after meiosis 1
Daughter cells
after meiosis 2
50
DNA Content
(arbitrary units)
The DNA content of nerve cells at G1, mature sperm, and gut endothelial
cells at G2 have been measured and plotted on the graph below. Based on
the data in the graph, which DNA sample is the nerve cell?
A. Sample 1
B. Sample 2
C. Sample 3
40
30
20
10
0
1
2
Sample
3