Meredith Hawkins
Lesson Sequence Report for General Biology
Mendelian Genetics Unit
November 26th to November 30th
Lesson summary
This lesson sequence covers an introduction to genetics, in particular, Mendelian
genetics. Students will be asked to play the part of Gregor Mendel and create their own
rules concerning how traits are passed from parent to offspring. After a brief
introduction, students complete a lab in which they use flowers to self-pollinate or cross
pollinate to generate “offspring.” The following day as a class the students work through
the “data” to determine what it means. The data shows the 16 offspring height from five
different crosses (tall x tall, short, x short, tall x short, hybrid tall x hybrid tall, hybrid tall x
short). During the class discussion, students work to develop rules or laws as for how
traits are passed from parent to offspring. Students also work to generate their own list
of vocabulary terms and their definitions.
The following day probability is introduced through a discussion using straws of
various lengths and having students predict the possible outcomes, for example, what
are the chances of picking the shortest straw? After this, Punnett squares are
introduced. Students work through examples as a class then use the ideas to complete
examples on their own. This is followed by an assessment (quiz) covering terms,
probability and Punnett squares.
Lesson Story
The lesson sequence starts with the beginning of the new trimester so part of the
first day involved introducing the students to the Biology B class and taking care of
procedural task. Otherwise, I was able to stick mostly to the plan. Once things calmed
down the students were asked to complete a quick write about what physical traits they
share with their parents or family members. Once the students have completed this we
take a few moments to share responses. Since it is a small town, many students
comment on other students responses. One student put down that he looks nothing like
his father while the rest of the class argued that he is the spitting image of his dad. The
class then has a discussion as to why they look like their family members. Students call
on their previous knowledge to give answers like “DNA” or “Genetics.”
At this point, I had the students take notes over Gregor Mendel and his
experiments. I included information about his life such that he was born into a poor
family and had a classic case of test anxiety so that students can relate with his life. The
notes also covered why Mendel started his experiment in that he saw two plants in the
monastery garden, one of the usual variety and one of a unique variety. I asked the kids
if they knew why they looked so different and some of them said “I don’t know.” So I
asked “Well, how would you find out?” and they kids answered mostly with “research” or
“search the internet.” I then explained that Mendel did the same and found the current
thought to be “the environment shapes how organisms look.” We also talked about why
this makes sense in that they look like their parents and for the most part, they live with
their parents.
At this point, the students are given “pea plant flowers” and asked to cross
pollinate and self pollinate the flowers to gain offspring. Students worked with
determining how to pollinate the flowers and how they would prevent pollination.
The following day students are given data. The data showcases five different
crosses – purebred tall x purebred tall, purebred short x purebred short, purebred tall x
purebred short, hybrid tall x hybrid short, and hybrid tall x purebred short- and given 16
offspring height. Since the students are given only pea plants heights, we discuss terms
we can use. One class decided to use the words “Giant and Midget” while another went
with “Tall and Short,” which we define as tall being over 6 feet tall and short being below
2 feet tall. We discuss how there are no examples of pea plants between 2 feet tall and
6 feet tall. When then use the data to complete a chart to help better analyze the data.
As we work through, students start to see how tall will mask short when crossed and
that. We also discuss how the parents of the parents play a role in offspring’s traits. The
students see the parents can be themselves mixed for the two traits. From this, the
students are able to bring in terms like “purebred” and “hybrid” from their knowledge of
dogs and cars. The students also recognized that something needed to be passed from
parent to offspring and that for pea plant height, the plants must have two of these, one
from each parent. I asked the students “What would you like to call this something?” At
first the students wanted to say “Genes” but then we talked about how genes can be
confusing because we often say we have a gene for hair color or a gene for eye color
but in truth we have “two of this something for each trait.” At this point, a student
suggested the term “thingys” and we went with it.
The next day we reviewed some of our terms, putting each term and it’s definition
up on the board. As we went, I threw in “What scientist call” these same terms. The
students were excited to see that their terms were similar such as tall for giant or that
their terms were right on, purebred and hybrid. I then helped them change their other
terms such as “thingys” became alleles. I also used this time to introduce words like
“homozygous,” “heterozygous,” “genotype” and “phenotype” for the students.
The students then had a quick write over what they thought the word “Chance”
meant. To help them, I even gave the example of “What are the chances of Michael
making a basket at tonight’s basketball game?” After this we had a discussion as to
what chance was. Then I had four volunteers come to the front of the room. Since I just
received turtles as a class pet from previous students, I told the kids that from my four
volunteers we would pull straws to see who would have to come in at lunch to help me
clean the tank. I told them that who ever pulled the smallest straw would be coming in.
We then predicted what would be the chance of each person grabbing the small straw. I
asked why the odds was the same for each person and we talked about how for each
person there are still four straws and each person has a chance of one in four of pulling
the short straw. We then discuss what is the percentage for each student to help the
students work on converting odds or ratios to percentages. Afterwards, I have them pick
straws. I then recollect the straws and have the students re-pick straws since “it’s such
a big job and Nicole can be expected to do it all herself.” Before we pick, I have the
students discuss what the odds are this time for getting the short straw. We talk again
about why they are the same. I then have the students pick. In my 3 rd hour, both times,
Nicole pulled the short straw. We then used this to discuss what are the odds of per
pulling the short straw three times in a row. This helps to have the students practice
multiplying fractions.
I then explain to the kids that with our knowledge of genetics could we predict
what traits an offspring has. Some students said “yes” and explained that with our pea
plants, we knew that all of the offspring from two purebred pea plants would be tall.
Another student said “No” and explained that she has an older sister and that her
parents thought she would look just like her sister but she doesn’t. The student also
went on to say that “Just because you have a good guess for something, doesn’t mean
it will be correct.” At this point, I introduce Punnett squares as a tool for helping scientist
to predict genetic outcomes and as a class we complete a Punnett square worksheet.
The following day, the students came in and had a quick write asking them to
predict the offspring from parents who had heterozygous brown eyes and homozygous
blue eyes. As we go over the question, I explained to students that in humans eye color
is determined by many genes and that is why we have such a range within eye colors,
for example blue eyes means blue eyes, light blue eyes, hazel eyes, and purple eyes.
After we completed the Punnett square, I explained that this problem comes from my
own family. My mother has heterozygous brown eyes since my grandfather had blue
eyes and my grandmother had brown eyes. My dad has blue eyes. I then ask the kids to
predict how many of my two siblings have brown eyes and how many have blue eyes?
The class guessed and came to the consensus that since I have blue eyes, at least one
of my siblings must have brown eyes. I then explain that all three of us have blue eyes.
A few students made jokes about my family which we all laughed at but I explain even
though for each of us kids, the predicted ratio is one to one for brown eyes to blue, that
it is still possible for the actual to be different.
At this point, I have the students complete Punnett Square Practice Lab Activity
in which students complete a Punnett square predicting results for a double
heterozygous cross. Then the students use cut paper that has on one side “A” and on
the other “a.” Each group of two students places their cards in a couple. The students
then shake and pour out their cards. The students must record what sides are up for 10
and 100 tosses. Then we collect their 100 tosses data and compile a list to have a
1,000 toss data.
The following day the students were given an opportunity to finish up the lab
activity. Once they completed that they were given another Punnett square worksheet to
help them get more practice and have examples so that they could get help. Once the
worksheet was completed and we went over it as a group, the students were given the
Punnett square quiz as their assessment for the sequence.
Description of students work
Many of the students struggled with working on the first day of the new trimester.
Since many of their classes were the first half of the class, students were not completing
many assignments that day. Many of my Biology B (the second half of biology class)
students were surprised to see that not only did I plan on them taking notes but also
completing a lab assignment. Because of this, some students completed the
assignments with ease and diligence while others blew it off more.
The pollination lab was difficult for students, mostly because it didn’t seem to
connect into with what I was asking them to do and what was expected of them. Many
of the students struggled as to what pollination was and how it was completed. Other
students struggled with how self pollination and cross pollination differed. A few
students thought that self pollination could only occur within the same flower, not
realizing the genetic component and those flowers from the same plant would be
genetically the same, thus making pollination with the same plant still self-pollination.
Many students also struggled with how to prevent pollination. Because the students
associated pollination with bees, many of the students said that to prevent both selfpollination and cross-pollination that they would need to use an insecticide and kill any
bees in the area. The students were able to see how to move pollen and that using a
pipe cleaner or a paint brush could help achieve this in a controlled setting. This lab also
lacked the opportunity for students to make predictions helping to connect it to further
activities.
During the class discussion review the data, the students had difficulties grasping
where the information was coming from. They could see it was crosses and what was
being crossed but they were unable to see any value in it other than this is the
information given to us. The students also struggled with creating their own terms and
definitions. They were excited to see that their terms such as “Giant” and “Midget” could
be scientifically used. Often times, their terms or slang is often no accepted so they
were very happy to see that how they express themselves could be used. With this, the
students were excited yet surprised for their own definitions. When asked “what does
dominant mean?” When a student went into a story about how he dominated a fight and
kick the other kids butt. He was surprised to see me write on the board “kicks the other’s
butt” When then discussed how this might not be the best definition and that saying it
mask the other trait but the kids were able to make a connection to the content and see
it in their own terminology.
Students at first struggled with how to set up and start a Punnett square. This
was still evident in the final assessment because students were still mislabeling
heterozygous dominant and homozygous dominant parents. The students also had
difficulty with how Punnett squares only showed predicted outcomes and not actual.
Throughout the entire lab students could see that their numbers were different but could
not see how they were different or how to compare it. Changing the question or having
students reduce their ratios might help students to see this relationship. Students also
struggled during the lab to see that the more data you work with (the 1,000 tosses
series) the more accurate your predicted information will be. It may be more beneficial
to review probability and use a simplistic method first of flipping a coin.
The class discussion as analyzing data and creating rules and terms for how
traits are passed was extremely helpful in seeing how students understand the nature of
science. Many students were left with questions afterwards as to how does human traits
fit into this – “Does human height work the same?” or “What traits are dominant to other
traits?” Students wanted to probe deeper into the material beyond what they knew of
pea plants.
The sequence was only partially inquiry in that students were unable to generate
their own questions and predictions. In future classes Students would be able to get a
better experience of this by incorporating more opening questions and brainstorming but
students were able to develop their own laws and terminology based on patterns within
the data provided to them.
What I would change
To make the lesson sequence more inquiry driven, I would change how much I
stressed Mendel’s life. Often times, when you ask students to take notes, they focus on
that part of the lesson since it was teacher derived and not their own observations and
data. Instead of focusing on who Mendel was, have the students focus more on what
Mendel saw could be a way to integrate more inquiry into the lesson and more value for
the students. I could start the unit with a picture of two plants, one the normal variety
and one a unique variety and have student guess why the two plants are so different in
appearance. After we have brainstorm for a bit, students could suggest their answers
(environmental causes, hormonal changes, or genetic causes) and I could lead students
into how genetics play a role in why the two plants are different. Then have the students
discuss how to examine the genetics and formulate an experiment involving crosses or
breeding plants together to view their offspring.
The opening pollination lab desperately needs to be changed. Students were
hung up far too much on pollination and not on making connections to the data that
would be presented in future class activities. The students also were unable to make
predictions about the crosses, as a true inquiry lesson would allow them. In future
classes, I will have the flowers sorted by genetic make up. Instead of one vase with all
the flowers, I will have the flowers in three vases each labeled with the plants genetic
traits. For example, one vase will be purebred tall, another purebred short, then hybrid
tall. Then the kids will have the opportunity to cross the plants and make predictions and
make connections to the data in the next activity. Students would still need to be
assigned to a specific cross to make sure each of the crosses was covered. This will
also help when students get to their cross’s data. This will help them to see that it is
data from their cross and not just numbers being thrown at them. I would also possibly
eliminate a cross between hybrid tall pea plants and purebred short pea plants. This
cross although shows another cross between pea plants doesn’t allow students to gain
any additional information from the crosses but can confuse them as to whether tall pea
plants does in fact dominant over short pea plants.
The student also struggled with how tall is a tall pea plant and how short is a
short pea plant. I think to help this it might be needed to have a visual reference in the
classroom. Using rolled paper, I could make a paper pea plant for the classroom wall
that is 6 feet tall and have another that is 18 inches tall to help students understand how
dramatically different these two types of pea plants are.
I also found that after this sequence when we started discussing meiosis,
students could not make a connection between meiosis and Punnett squares. I think it
would be more helpful to have the students, once they understand meiosis, complete
Punnett squares using chromosomes halves with alleles on them, to help students see
that through meiosis the alleles are able to split and allow for Punnett squares to
actually predict results. This could also help in later units for students to see how
genetic disorders could result from incomplete segregation during meiosis.