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Tracking genes through meiosis
Consider a cell from a male diploid animal that has two pairs of chromosomes. Use the drawing, your
notes and paper models to track how meiosis affects the distribution of the four chromosomes by
identifying a specific gene associated with each chromosome.
b
S
B
s
homologous
chromosomes
b
B
B
b
s
S S
Nuclear
Membrane
s
Centromere
Interphase
Metaphase
Procedure:
1. Obtain 8 pieces of paper, 4 of each color and 4 paper clips. (in the envelopes on the lab tables)
2. Identify a single gene on each chromosome of the 4 original chromosomes by writing the following
letters on each: B = Brown eye, b= blue eyes (on the larger chromosomes), S = dark skin, s= light
skin(on the smaller chromosome). Put the labels for eye color on the long chromosome, and the labels
for skin color on the short chromosome. See the above drawing.
3. As meiotic cell division begins, each chromosome makes an identical copy of itself during interphase,
which remains attached to the original chromosome at the centromere. At this point, each
chromosome is made up of two Chromatids. Each chromosome becomes visually shorter and thicker
as it folds multiple times upon itself. . Include the same letters on the new chromosomes. Use paper
cut-outs of same colors as the original 4 and form two pairs of homologous chromosomes. A paper clip
will act as the centromere.
4. Now that you have the chromosomes paired up (prophase) you’re ready to demonstrate the rest of the
process. Move your chromosome models through the process of meiosis finishing with a gamete. You
should be able to demonstrate, prophase, metatphase, anaphase and telophase I and prophaseII,
metaphaseII, anaphaseII and telophase II.
5. You also need to include crossing over. To demonstrate crossing over, cut the segment of the
chromatid off and cross it over with the other. To demonstrate crossing over, cut the allele (letter) and
replacing it with another from the homologous chromosome. Tape the cut pieces together.
6. Complete the analysis questions. (one per group) When finished, the teacher will check your group’s
simulation of meiosis. This needs to be mastered before signing it. The teacher will sign you’re lab
notebook.
Tracking genes through meiosis
ANALYSIS QUESTIONS: - Complete in your lab notebook:
1.
What is the Diploid number of the original cell?
2.
What is the haploid number in the gamete?
3.
Draw the chromosomes appearance and label the stages during meiosis using the diagram below as a
template.
Meiosis I
Meiosis II
4.
Describe the possible allele (letter) combinations at the end meisosis.
5.
What is crossing over? And describe the importance of this event.
6.
One form of Down syndrome is known as trisomy 21 because affected individuals have three No. 21
chromosomes in their somatic cells.
a. How many No. 21 chromosomes should the cells have?
b. How many should the gametes have?
7. List 3 ways meiosis is different from mitosis?
8. What are two reasons meiosis is important in living things?
9. Contrast the terms chromatin, chromatid and a chromosome?