REEBOPS LAB: Marshmallow Meiosis
Background:
Reebops are tiny creatures that live in discarded pop
cans and shoe boxes. They are difficult to observe in the
wild because they are shy and move very quickly. Reebops
are prolific breeders in captivity and thrive with minimal
care. They inherit traits in the same way as humans so they
are excellent subjects for studying genetics. Chromosomal
analysis has revealed that this unusual species has 16
chromosomes (8 homologous pairs).
In this activity, you will simulate the reproduction of
2 Reebop parents and construct the resulting offspring. You will use concepts of meiosis to sort the
parents’ chromosomes and form their gametes then use the information to determine the baby
Reebop’s traits. After the baby Reebops are born, the siblings will be assembled in a nursery so that
their traits can be analyzed.
Purpose: to model and interpret the role of meiosis in sexual reproduction.
Materials: Paper homologous chromosomes (Mom’s set=pink; Dad’s=blue)
Large marshmallows, small colored marshmallows, push pins, pipe cleaners, thumbtacks, nails,
toothpicks (to attach marshmallows to each other)
Procedure:
1. Observe Mom and Dad Reebop and record their phenotypes.
A. __________________________________________________________________
__________________________________________________________________
2. Open the envelope, take out all the cards and turn them face down, keeping Mom’s (pink) and
Dad’s (blue) separate as you sort them out.
B. How many chromosomes does each parent have? _____________________
3. Sort each set of chromosomes into pairs of the same length (homologous pairs).
C. How many homologous chromosomes does each parent have? ______________
D. Why does each reebop have 2 alleles for any given trait?
4. Randomly take one chromosome from each pair of Mom’s chromosomes and place in a pile. This pile
is the ‘female gamete’ (egg cell).
E. Is the female gamete diploid or haploid? ___________How do you know?
F. What type of cell division makes eggs? __________________
5. Randomly take one chromosome from each pair of Dad’s chromosomes and place in another pile.
This pile is the ‘male gamete’ (sperm cell).
G. Is the male gamete diploid or haploid? _____________How do you know?
H. What type of cell division makes sperm? __________________
6. Put the chromosomes you haven’t used back into the envelope.
7. Fertilize the female gamete with the male gamete by mixing together the female and male
gamete piles. This is now your selection of ‘baby genes’ (the zygote chromosome set). Sort out
the chromosomes of your new individual into homologous pairs.
I. How many chromosomes does your zygote have? __________
J. How does this number compare to the number that each parent has? ______
K. Is the zygote haploid or diploid? _____________
L. What has to happen to the zygote next for it to develop into a baby?
H. Write down the letters you have obtained in Table 2 for your ‘baby Reebop’. For example, if
you have one card with the letter A and another card with the letter a, your genotype is Aa.
I. Use the ‘decoder key’ to decide what the phenotype of your baby Reebop will be based on your
genotype description. Record in Table 1.
J. Collect all the materials you need for your baby Reebop and build your baby Reebop. Join the
marshmallows with toothpicks. Draw your baby reebop below.
K. Take a look at all the reebops made by your classmates. You should notice that each is
different. There are several processes that make genetic diversity possible.
i. What process happens in meiosis?
ii. How does fertilization increase further genetic diversity?
iii. Why are brothers and sisters different even if they have the same parents
L. Put your baby in the Reebop nursery with the other newborns!
M. In Table 1, star the Reebop traits that show incomplete dominance. Explain why you picked
these traits.
Table 1: Decoder Key
Trait
antenna
humps
nose
tail
eyes
legs
body segments
sex
Genotype
AA
Aa
aa
MM
Mm
mm
QQ
Qq
qq
TT or Tt
tt
EE or Ee
ee
LL or Ll
ll
DD or Dd
dd
XX
XY
Table 2: Baby Reebop genotype and phenotype
Chromosome
Alleles
Phenotype
1 antenna
2 antenna
no antenna
1 green hump
2 green humps
3 green humps
red nose
orange nose
yellow nose
curly tail
straight tail
2 eyes
3 eyes
clear legs
colored legs
3 body segments
2 body segments
female
male
Genotype
(also record if
pure-bred or hybrid)
1
2
3
4
5
6
7
8
Parts used
nails
colored marshmallows
colored marshmallows
pipe cleaner
silver tacks
push pins
large
marshmallows
bow on head or
bowtie
Phenotype
Discussion and Conclusion: Answer in complete sentences! Most of the lab points will come
from this section.
1. Reebops have a diploid number (2n) of 18. Explain how the diploid number of chromosomes is
maintained from one generation to the next. In other words, why did the baby reebop have 18
chromosomes instead of 36? (4 pts)
2. For any given trait, how many alleles does the baby reebop have? Explain where these alleles
came from. (2 pts)
3. Each parent reebop was heterozygous for each trait. Explain what this means. (2 pts)
4. Children from the same parents are not exactly the same. Explain why this is true based on the
reebop activity and what you know about meiosis. (4 pts)
5. Fill in the following table:
Trait
Punnett square to predict %
Curly tail
Calculate actual % in nursery
3 humps
5. Write a paragraph (5 sentences minimum) to describe your predictions in #5 and explain why they
were or were not the same as the actual results in #6. Were the actual results the same as the
predictions you made in #5? Explain why or why not. (10 pts)