REEBOPS LAB REPORT
LAURA CAPPS
FEBRUARY 18, 2013
INTRODUCTION
“I have my mom’s eyes and my dad’s ears.” “Well, I have my dad’s hair and my mom’s
nose.” Statements like these are common for children to make as they progress through school.
They begin to compare themselves to other students and to their family members. Observations
lead to questions such as why there are differences between people, even in the same family.
These are questions that deserve answers. The answers to these questions are found in the realm
of genetics, a subject many elementary teachers may not expect to cover. While the fine details
of genetics may be too difficult for younger children, the basics are very accessible to them. In
order for teachers to be able to answer the questions their students may have, the teachers
themselves need to have a solid understanding of the subject. They also need to understand how
to make the material relatable to their young students. Our Reebops experiment is perfect for
both of these goals.
This lab ensures that we get a lot of practice with crosses between two organisms, both
monohybrid and dihybrid crosses. By performing the crosses, we are allowed to take the abstract
ideas learned in class and apply them to an actual situation. We can go through the process step
by step and see how certain outcomes came to be. The processes of sexual reproduction and
independent assortment become accessible, which increases understanding. When someone
understands a concept well, they are able to explain it well. As teachers, explaining is our job.
The Reebops lab is also a good way to explain genetics to elementary children. Reebops
are easy and cheap to make, have a short reproductive cycle and can be easily manipulated by
children. Using paper chromosomes, students can actually go through the process of choosing
the genotype of their Reebop and build their own Reebop, like we did in lab. Punnett squares can
also be introduced as a way to predict the possible outcomes of the chromosome selection.
Prediction is a big part of the elementary science standards and genetics is a prime subject to
practice probability and prediction.
Part of predicting is formulating hypotheses. This lab required four hypotheses, since
there were four sets of data to analyze. For the first set of data, concerning the trait for antennae,
my hypothesis was that this trait is autosomal, meaning it is found on a chromosome that does
not determine sex of organism, and undergoes the process of independent assortment. My
hypothesis for the next set of data, the trait for number of body segments, was that this trait also
was autosomal and undergoes the process of independent assortment. However, this was a
hypothesis that needed to be revised. I will further discuss the revision in the Conclusions section
of this paper. The third set of data focused on the traits for tails and ears. My original hypothesis
for these traits was that they were both autosomal and undergo the process of independent
assortment. This hypothesis also needed revision and will be discussed in the Conclusion section.
The fourth and final set of data focused on the traits for leg color and number of eyes. My
hypothesis for this set of traits was that both traits were autosomal and undergo independent
assortment.
The basis for each of these hypotheses comes, in part, from work published in 1866,
before DNA was even known to exist. An Austrian monk and mathematician named Gregor
Mendel did great work in the field of genetics, doing crosses of pea plants. Similar to the crosses
performed in this lab, he focused on traits that only had two clear cut outcomes, such as round or
wrinkled peas and purple or white flowers. The result of his work resulted in the formulation of
the principles of independent assortment and segregation. Both principles were applied in this
lab. The principle of segregation, stating that sexually reproducing organisms have two alleles
that separate during the production of gametes, was applied every time we did a cross of two
organisms. In the resulting offspring, there was only one allele from each parent. The principle of
independent assortment, stating that each pair of alleles on homologous chromosomes is
distributed independently from every other pair, is a key element in every hypothesis. Through
his work, Mendel discovered that the placement of alleles into gametes is random and is not
influenced by the placement of other alleles. This principle is important in explaining why there
can be multiple outcomes for one cross and therefore is included in every hypothesis.
Every hypothesis also predicts that the traits being worked with are autosomal, meaning
they are not found of the chromosomes that control the sex of the organism. This is specified
because there are traits that are found on only the sex chromosomes, the X and Y chromosomes
in mammals. The expression of these sex-linked traits can be different than the expression of
autosomal traits. One purpose of this lab is to determine which traits are sex-linked and which
are autosomal based on provided information. Because there is only one pair of sex
chromosomes and multiple pairs of autosomal chromosomes, there was a greater chance that the
traits would be autosomal rather than sex-linked. Therefore, each original hypothesis states that
the traits are autosomal rather than sex-linked.
METHODS
To test these hypotheses, I had to use a combination of tools. I used information given to
me in my lab packet, Punnett squares and chi-squares. The information in the lab packet was the
traits to test, the phenotypes and genotypes of the parents and the observed number of
grandchildren or F2 generation for each trait. The data was sorted by trait observed, gender and
variation of the expressed trait. For example, I was told that 127 females had 2 body segments.
In order to test whether each trait was indeed autosomal and underwent independent
assortment, I needed to first use Punnett squares to determine the probability of each possible
phenotype for each trait. For each trait, the parent, or P1, generation was crossed first resulting in
the F1 generation. Then the F1 generation was crossed resulting in the F2 generation. The
Punnett squares gave me the expected ratios for each genotype and phenotype of that particular
trait. I used the expected phenotypic ratios and the F2 generation information provided to me to
create chi-squares.
The chi-squares are what I used to test the hypotheses. They are used to determine
whether or not a hypothesis should be rejected or accepted, based on the p-value that is produced
as a result of completing the chi-square. I completed a chi-square for each hypothesis and used
that to determine if my hypothesis should be revised or not.
RESULTS
*See attached Data Tables, Punnett Squares and Chi-Squares
Of the four crosses, two were monohybrid crosses, meaning there was only one trait on
which I focused, and two were dihybrid, meaning that there were two traits on which I focused.
The first monohybrid cross focused on the trait for antennae. After crossing the P1 generation,
the F1 phenotypic ratio was 4/4 or 1, meaning that all offspring had the same phenotype. After
crossing the F1 generation, the phenotypic ratio was 3:1, meaning three of four offspring have
the same phenotype while 1 is different. The chi-square value for this cross is 0.857. Using the
degrees of freedom, which was 1, and a chi-square table, the p-value was determined to be
greater than 0.30.
The second monohybrid cross focused on the trait for number of body segments.
Crossing the P1 generation resulted in an F1 phenotypic ratio of 4/4 or 1; crossing the F1
generation resulted in an F2 phenotypic ratio of 3:1. These results were consistent with the first
monohybrid cross. However, the chi-square value for this cross was 158.096 and the p-value was
less than 0.01, even with the same degrees of freedom as the first cross. Because this p-value did
not support my hypothesis, I had to revise it and create another Punnett square and chi-square for
this trait. The revised cross of the P1 generation produced an F1 phenotypic ratio of 2:2; a cross
of the new F1 generation produced an F2 phenotypic ratio of 1:1:1:1. The revised chi-square had
a value of 0.372. The degrees of freedom was 3 and the p-value was greater than 0.30.
The first dihybrid cross focused on the traits for the tail and ears. The crossing of the P1
generation resulted in a phenotypic ratio for the F1 generation of 16/16 or 1. The crossing of the
F1 generation resulted in a F2 phenotypic ratio of 9:3:3:1. The chi-square value for this cross
was 361.112 with a degrees of freedom of 3. The p-value was less than 0.01. As with the second
monohybrid cross, I had to do a revised version of this cross, resulting in a second Punnett
square and chi-square. The second cross of the P1 generation resulted in an F1 phenotypic ratio
of 8:8. The second cross of the F1 generation resulted in a phenotypic ratio for the F2 generation
of 3:3:1:1 for females and 3:3:1:1 for males. The new chi-square value was 5.801 with a degrees
of freedom of 7. The p-value was greater than 0.30.
The second dihybrid cross focused on the traits for leg color and number of eyes. After
crossing the P1 generation, the F1 phenotypic ratio was 16/16 or 1; after crossing the F1
generation, the phenotypic ratio for the F2 generation was 9:3:3:1. The corresponding chi-square
had a value of 2.421 and the degrees of freedom was 3. Therefore the p-value for this cross was
greater than 0.30.
CONCLUSIONS
After completing all of the Punnett squares and chi-squares, I had enough information to
determine whether my initial hypotheses were supported or not. The results were mixed. Half
were supported and half were not. My hypothesis that the trait for antennae is autosomal and
undergoes independent assortment was supported. After completing the chi-square, I had a pvalue of greater than 0.30, which falls under the accept portion of a chi-square table. The F2 data
makes sense for this cross because I know that for autosomal traits, the F2 phenotypic ratio is
3:1, three with the expressed dominant trait for every one with the expressed recessive trait. The
F2 numbers demonstrate this ratio well. 615 males with blunt antennae is close to three times as
large as the 197 males who had sharp antennae. It also makes sense that there are two different
phenotypes because of inheritance and the principle of segregation. Inheritance is the fact that
parents pass down alleles to their offspring through their gametes, which are then combined
during fertilization. The phenotypes of the offspring depend on the alleles passed onto them from
their parents. Segregation states that alleles separate from each other in the formation of gametes.
Because of this principle and inheritance, parents can produce offspring that are either
phenotypically different or phenotypically similar to them.
My second hypothesis, that the trait for number of body segments is also autosomal and
undergoes independent assortment, was not supported. After completing the chi-square for this
hypothesis, I had a p-value of less than 0.01 which falls under the reject category of a chi-square
table. The F2 data did not make sense knowing that autosomal traits should have an F2
phenotypic ratio of 3:1. The F2 data did not represent this ratio; it had a 1:1 phenotypic ratio. So
I revised the hypothesis to say that the trait for number of body segments is sex-linked and
undergoes independent assortment. This hypothesis was supported; the p-value for the new chisquare was greater than 0.30 and therefore accepted. I know that the F2 phenotypic ratio for a
sex-linked trait is 1:1:1:1, with each gender having one of each phenotype. The F2 data matched
this ratio. The same principles of inheritance and segregation applied to this hypothesis just as
they did to the hypothesis about antennae.
The third hypothesis, stating that the traits for tails and ears were both autosomal and
undergo independent assortment, was also not supported. After completing the chi-square for this
cross, the p-value was less than 0.01 and therefore rejected. The F2 data did not make sense in
the light of the rules of genetics because for autosomal traits, the F2 phenotypic ratio for two
traits should be 9:3:3:1. However the given data for tails and ears do not match up with this ratio.
So I revised my hypothesis to state that the trait for tails is autosomal and the trait for ears is sexlinked. I formulated this hypothesis based on the fact that the phenotypic ratio for an autosomal
trait is 3:1 and 1:1 for a sex-linked trait. I combined all of the F2 data for the tails and found a
ratio of curly to straight that equaled 3:1. I then added the F2 data for the ears and found a ratio
of ears to no ears that equaled 1:1. Therefore, I determined that ears were sex-linked and tails
were autosomal. I tested this hypothesis and found that it was supported. The p-value calculated
in the revised chi-square was greater than 0.30 and therefore accepted. The F2 data now made
sense because the F2 phenotypic ratio for a dihybrid cross with one autosomal trait and one sexlinked trait is 3:3:1:1 for females and 3:3:1:1 for males. The F2 data matched up with this ratio.
As with the monohybrid crosses, the principles of inheritance and segregation still apply to both
of these traits.
The fourth and final hypothesis, stating that the traits for leg color and number of eyes are
both autosomal and undergo independent assortment, was supported. The p-value was greater
than 0.30 and therefore accepted. The data also made sense because the observed F2 data was in
the ratio of 9:3:3:1 which is the F2 phenotypic ratio for autosomal traits. The principles of
inheritance and segregation still apply for these two traits as well.
In every experiment, there is room for error. In this experiment, there was the chance of
mathematical error and data error. This experiment involved a lot of math, much of which
included rounding. Because I did not use exact numbers, there was a margin for error. There also
was the possibility of miscalculations, like addition errors. Error can also be present in the data I
used. The data was given to me and could contain error for which I could not resolve. A third
source of error could come from the nature of this lab. Our experiment is a model of genetic
inheritance and therefore has limitations. Our model is simplified and cannot account for every
aspect of the complex process of inheritance.
Inheritance is the main topic of this lab. After completing this lab, it is apparent that there
is an inheritance mechanism which allows traits in occur in the parents to be passed down to the
offspring. Every offspring has traits that occur in either parent or grandparent. There are two
options for each trait and one of those options appears in every offspring; there is no random
third option that appears. The data shows that there is mechanism that allows traits to be passed
down from generation to generation.
As stated before, for each trait examined, there are two phenotypic outcomes. The
evidence suggests that these two outcomes remain distinct from each other; there is no blending
of traits. Blending can be found in humans; there are many different shades of hair color, not just
blonde or brunette. Blending does not appear to occur with these traits with Reebops. For
example, there can be red legs or blue legs. If blending occurred, there could be offspring with
purple legs, the combination of blue and red. However, there are no offspring with purple legs.
The same is true for every other trait examined.
The alleles that transmit the physical traits remain the same from generation to
generation. If the trait for antennae is represented by the letters B and b in the P generation, the
same letters will represent the trait in the F1 generation and the F2 generation. The combination
of alleles can vary from generation to generation but the alleles themselves do not change.
As discussed in the Introduction section, Gregor Mendel’s work resulted in the principles
of segregation and independent assortment. The principle of segregation states that sexually
reproducing organisms have two alleles that separate during the production of gametes. In the
resulting offspring, there was only one allele from each parent. There is evidence in my data that
supports this. Each offspring has one allele from each parent, not two.
The principle of independent assortment states that each pair of alleles on homologous
chromosomes is distributed independently from every other pair. Evidence for this principle can
be found in the dihybrid crosses. If independent assortment did not occur and alleles had a
specific order, such as dominant alleles on the left and recessive alleles on the right during
Metaphase I, the combinations Le and El would never occur. However, both combinations do
occur in the data. Therefore, independent assortment must occur.
Both parents contribute to the offspring; each parent contributes one allele per trait. Both
parents may not contribute to the phenotype of the offspring but both contribute to the genotype.
If one parent gives a dominant allele and one gives a recessive allele, only the dominant allele is
expressed in the phenotype; however, the recessive allele is important when the offspring
reproduces. The offspring can pass on the recessive trait when it reproduces.
There were a few rules of inheritance for which I had to make slight exceptions. Firstly,
the F2 data did not match exactly with the expected F2 phenotypic ratios; however the numbers
were close. I had to do this because this data was the only data with which I could work. If I did
not make this exception, I could not have proceeded with the lab. I also had to ignore the
possibility of mutations or other genetic malfunctions that could account for the F2 data. I had to
do this because I had no information about any mutations or malfunctions. I only had the
provided data and had to base my results and conclusions off of the information given to me.