Use of paper chromosomes:
Illustration of meiosis and crossing over.
Answer all bold questions IQIA in your journal. Directions for chromosome cut-outs:
1. Observe the chromosomes in set one with the symbols for maternal (from mom) and paternal (from dad)
AND color maternal chromosomes red (or pink) and paternal chromosomes blue.
2. Using set #2, create another four chromosomes identical to the four given. Color and label with the
correct letters (alleles).
1. What process did you accomplish when you created a second set?
2. When does the copying of DNA occur?
3. Cut out each chromosome: DO NOT MIX SETS UNTIL STEP 4!
4. In the middle of your desk top pair each maternal chromosome and paternal chromosome with its copy;
i.e. one big blue chromosome with the other big blue chromosome.
3. What is each part of a doubled chromosome called?
5. Now take each doubled chromosome and line them along side of the other similarly sized doubled pair.
You now have formed a tetrad. It consists of 2 homologous pairs of chromosomes; the duplicated
maternal and duplicated paternal chromosomes side by side. This tetrad is formed in prophase I.
4. Pick one chromosome and record what genes/alleles you would get if that chromosome
was passed on before crossing over (ie. ABCDEF)?
6. Now simulate crossing over. Cut segment A-B off of one of your chromosomes and segment a-b off
one another. Re-tape the exchanged pieces back onto the chromosome.
7. Choose any other gene segments for the other tetrad and exchange like-length segments (ie. J-K-L with
j-k-l). Re-tape.
5. Describe what you see; what alleles (letters) does each chromatid NOW contain?
6. When does crossing over occur? What stage of meiosis?
8. Now simulate the rest of meiosis. Line up each tetrad in a vertical fashion and separate homologous
pairs. This represents the events metaphase and anaphase of meiosis I.
9. Finish meiosis I by placing string around the chromosome sets to illustrate the fact you have two cells.
Note: you formed two cells but note that you don’t reform a nuclear membrane. You should have one
doubled chromosome in each of two cells.
7. Why would it make sense for the nuclear membrane to not be reformed at the end of
telophase of meiosis I? (hint: what has to happen again?)
10. Now simulate meiosis II (There is no doubling of the DNA/Interphase as in step 2 above). To do this,
line up each doubled chromosome vertically and then separate sister chromatids. This represents the stages
of metaphase and anaphase of meiosis II.
8. How many gametes cells do you have at the end of meiosis II? How many chromosomes
are in each?
11. Glue the chromosomes into your journal and draw a circle around each new daughter cell to simulate
nucleus reformation. You should have only one of each type of chromosome in each cell. Number your
cells 1-4.