Name: __________________________
Dance of the Chromosomes
DO NOT EAT ANY PART OF THIS LAB - ALL MATERIALS WILL BE USED AGAIN
Introduction:
This activity will model how chromosomes “dance” or move and sort during meiosis. You will be looking at the
chromosomes in a mythical mosquito. A karyotype of this mosquito has shown that it has three pairs of
chromosomes - the normal number for a mosquito. After building your mosquito chromosome models, you
will demonstrate the process of meiosis and determine which genes will be in the mosquito gametes. The
genes that an organism has are galled its genotype. From the genotype, you will determine the phenotype of
these offspring. A phenotype is what an organism looks like as a result of the expression of the genes.
Materials:
For each group of two students:
 1 airheads
 1 Black Sharpie
 1 coin
 1 plastic bag
Part A: Constructing Duplicated chromosomes (in partners)
1. Gather all materials
2. Construct 3 duplicated chromosomes using the figure to the
right as a guide.
a. Cut your airhead down the middle length-wise then cut
each half again length-wise. Set aside two of the four pieces.
b. Take the other two pieces and cut each width-wise about
2/3 of the way from the top.
c. You now have two long chromosomes, two medium-length
chromosome and two short chromosomes that have
duplicated. Two identical strands of DNA that result from DNA replication
are called sister chromatids.
d. Give each pair of sister chromatids a slight bend and
attach them in the middle. Although we do not model this, sister chromatids
are attached together at the center by a centromere.
How many chromosomes do you now have?
Why are the chromosomes different lengths?
Make a drawing of one of your chromosomes. Label: chromosome, sister chromatids, and centromere
Part B: Labeling Genes (in partners)
Use the table below to assist you in labeling your chromosomes with genes.
Trait
Abdomen Color
Wing Shape
Wing Length
Antenna Texture
Traits of the Mosquitoes
Phenotype
Symbol for
(Variant of Trait)
Allele*
Black
B
Orange
b
Round
R
Square
r
Long
L
Short
l
Hairy
H
Smooth
h
Chromosome
Long
Long
Medium
Short
The labeling of genes in the activity reflects the system used by geneticists. The uppercase letter
represents the dominant allele or trait; the lowercase letter represents the recessive allele. (For example,
in peas, the gene for the trait of pea shape can be R for round and r for wrinkled). An *allele is a different
form of variant of a gene for a specific trait. For example, the gene for shape has two alleles, R and r. One
allele results in round shape and the other results in wrinkled shape.
In this activity, each gene has two alleles. You will determine which allele is present on the chromosome
by flipping a coin. To assign the allele of your 4 genes, your group must make a total of 4 coin flips. Both
chromatids on a chromosome will have an identical allele and should be labeled.
3. Mark your long chromosomes with an allele for abdomen color using the symbols above. Be sure to mark
them in precisely the place shown in the diagram to the right.
a. Flip the coin once to assign the allele for abdomen color.
b. If the coin lands on heads, write the letter B (for black allele)
in the correct place on both of the sister chromatids of the long
chromosome. If the coin lands on tails, write the letter b
(for orange allele) on both sister chromatids.
4. Mark both of your long sister chromatids with an allele for wing shape as
described above. Remember to mark the same allele in the correct
place on both of the sister chromatids.
5. Mark the allele for wing length as above on your medium chromosome.
6. Mark the allele for antenna texture on your short chromosome.
What does the placement of alleles on the chromosome represent?
Part C: Forming Homologous Chromosomes (group of 4)
7. Find another pair that is ready for part C and that has a different color of airheads and place them together
on a desk or lab bench.
Your group now has 6 mosquito chromosome models. The models represent 3 pairs of homologous
chromosomes. Homologous chromosomes are chromosomes that have genes for the same trait at the same
location. You have three maternal chromosomes (from mom) that are one color, and three paternal
chromosomes (from dad) that are the other color.
Explain how your models represent homologous chromosomes using the definition above
You now have alleles for each of the 4 known genes on your 6 chromosomes. The alleles represent the
genotype of your mosquito. The figure below shows one example of one possible result of the coin flips
(assignment of alleles) along with the genotype for the mosquito that results.
Genotype: Bb, rr, LL, Hh
Analysis Questions:
1. Make a diagram of your six chromosomes like the one above. Label: chromosome, sister chromatids,
maternal chromosome, paternal chromosome, homologous chromosomes, centromere, allele
2. What is the genotype for your mosquito?
3. What is the phenotype for your mosquito?
4. What do the two colors represent?
5. Why are there two chromatids in each of the chromosomes?
6. What do capital letters represent? Lower case letters?
7. Why are alleles for each different gene identical on sister chromatids?
8. Why might alleles on homologous chromosomes be different?
9. What is the difference between an organisms genotype and phenotype?