Modeling Genetics

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Objective

Students will model how biological traits are passed on to successive generations.

Big Idea

Hereditary information, coded by DNA, is passed down from generation to generation in a predictable way.

Warm-Up

5 minutes

Warm-Up: Why is it impossible to see a hybrid organism if it has a recessive trait?

Activate students’ prior knowledge from the Genetics lessons, Mendel's genetics and Who's genes are you wearing? Be prepared to stimulate students’ thinking with questions like, “What does hybrid mean or what is a recessive trait”, as a means to get them thinking before they attempt to respond to the question.

This question serves as a great way to lead students into a quick review.  Look for students to be able to communicate that hybrid means mixed traits organisms and that recessive traits are not demonstrated in the phenotype when part of a gene that also has a dominant allele. Make a point to help students use the use the academic vocabulary in their responses in order to increase their academic literacy.

Content Review

10 minutes

Share the learning targets for today’s lesson:

  • I can analyze how biological traits are passed on to successive generations.
  • I can comprehend Mendel’s laws of genetics and how these laws affect variability within a species.

Conduct a brief review of key concepts using inquiry-based questions that allow students to demonstrate what they know and how familiar they are with key terms.  Ask questions like:

  • How is an allele related to a gene, or
  • How is homozygous different from heterozygous? 

Conduct this review as a whole class discussion, eliciting responses from students who volunteer to answer questions, as well as those who do not.  Look for students to be able to explain that an allele is represented by one letter and a gene is represented by two letters. Students should know that the inherited trait is represented by the gene. Spend time reviewing the language of the content and allowing students to practice using the terms appropriately in context, as well as pronouncing them correctly.  

If students do not display a working knowledge of the terms, conduct a spiral review of the content and vocabulary, take time to conduct a quick spiral review of the concepts.  Spend time re-teaching the meaning of the latin root words, homo- and hetero.   Repetition leads to a deeper impression for many students and this type of academic discourse helps greatly to enhance the learning.

Guided Practice

10 minutes

Display the Baby Reebop Lab Directions.   Explain that the lab will be conducted in groups of two students.  Prior to the class, decide if the groups will be pre-assigned or if students will be able to choose their work partners.

Using an LCD projector and interactive pad, guide students through a summary of the lab procedure:

  1. Show students how they will separate the strips found in the envelope by color; one partner will have blue to represent the paternal side and the other partner will take pink to represent the maternal side.
  2. Emphasize that student should keep the strips separated by color and in pairs.
  3. Point out that the strips have letters on them. With the letters face up, show students how to match each pair of letters in order according to the size.
  4. Model how to turn all the strips face down so that  you cannot see the letters.
  5. Explain that each student in the group will take turns and select one strip from each pair and place it back into the envelope, leaving the other paper strip from the pair on the table.
  6. Model how students will turn the remaining paper strips face up again so that they can see the letters.
  7. Match the letters (one blue and one pink).  Make sure students understand that the letter may be either uppercase or lowercase when matching.
  8. Model how to record the data for each trait on Table 1.
  9. Model how to use the traits list match the genotypes with the phenotypes in order to determine what supplies will be needed to make the Reebop.
  10. Model how students will use the Reebops Decoder legend and Table 1 to identify the parts needed to make the Reebop. 

While modeling the procedure for students, ask questions to further enhance students’ understanding of concepts before they are released to work independently:

  • What do you think the strips with letters represent?
  • Why are there two strips for each letter?
  • What do the matched pink and blue letters represent?

Preview the Lab Analysis Questions so that students will be aware of what they are expected to observe, know or be able to do at the end of the lab.  It’s important to do this because students often lose sight of the purpose of a lab and fail to demonstrate the knowledge that the lab was intended to build.

Independent Practice

25 minutes

Distribute Make a baby Reebop lab instructions and lab write-up forms to each group of two students.  Allot 5-7 minutes for students to read the lab.  After the time has passed, release student groups to complete the lab.   Instruct students to work in groups of two to create the Reebop.  Make sure that students understand that each person is expected to complete his/her own lab-write-up.

Remind students that one person from each group should bring the envelope with ALL of the chromosomes they randomly selected and the shopping list to the teacher to collect the Reebop parts. 

Walk around to observe and listen to groups as they work.  Use questioning to guide students’ thinking when it is observed that students are not making the expected connections to draw the correct conclusions.  

Point out how the collection of chromosomes is a random process, pulling  one allele from either parents' genes to determine the traits inherited by the Reebop.

After students make their Reebop, check their finished product against the genotypes listed on the Lab sheet. Affirm the accuracy of their work or re-direct them to go back and re-work their Reebop.

Allow students to work together to complete the lab analysis questions.  Allowing students to work together gives them an opportunity to pool their collective thoughts to develop sound written responses to the questions.  It also requires them to talk and possibly defend their answer against their partner's answer, which is a higher order thinking skill.

When students complete the Reebop and the lab questions, collect the lab write-up forms.  Read students' responses to the questions, noting if they were able to correctly respond to the question.  In particular, note is students were able to correctly deduce what would happen if the parents' chromosomes failed to separate during meiosis.  This type of question is a higher level question that requires students to take what they know to make a prediction.

The student work sample that is included shows that the student possesses an understanding of the concepts, given that the student's responses to the questions are accurate and he is able to correctly use the associated vocabulary in his responses.

Close

5 minutes

Ask students if they have a better understanding of how siblings do not necessarily look alike, now having modeled genetics.  Ask what part of the lab made the concept clearer.

Listen for students' ability to convey that they know that genetic variation results from crossing over of chromosomes. Listen to see if they are able to convey that probability of inheritance is random. Encourage students to use the vocabulary  of the standards in their conversations.   Expect students to attribute their increased understanding to the blind pull of traits they conducted to determine the traits that the Reebop would have.  This simple activity is a powerful method to increase understanding of how the inheritance of traits is the result of random assortment of traits from both parents.