"X" Marks The Spot
Lesson 8 of 13
Objective: SWBAT demonstrate their understanding of genetics by applying the concept of "X" chromosome inactivation to explain the variation of traits that are observed in a population.
Students will watch the video clip which will serve as the direct instruction for today's lesson. Students will record notes during the 6 minute video and the class will conduct a quick whole-group review to discuss the most interesting highlights about the concept of "x"inactivation. Students will be encouraged to ask questions and seek clarification during our class discussion.
X-inactivation occurs because females are XX and have two copies of the X chromosomes. One of the X chromosomes must be turned off so the genes on the other X chromosome can be expressed.
Students will use the flip of a coin to represent the turning off of one of the female x-chromosomes which occurs in the human body at the 32-cell stage.
- If the students flip a heads up on their coin - the XB (dominant trait) will be shut off leaving the Xb allele to be expressed at a patch of orange fur.
- If the students flip a tails up on their coin - the Xb(recessive trait) will be shut off leaving the XB allele to be expressed at a patch of brown fur.
Sample of Student Work: Creating The "X" Cats #1 - All student work samples will represent a different color combination pattern to demonstrate the x-inactivation randomness during the embryonic stage of development.
Sample of Student Work:Creating the "X" Cats #2 - This activity enabled students to experience the independent nature of each trial because many students flipped multiple heads in a row and a multiple tails in a row. When students were asked the probability of flipping a heads next . . . they contemplated and responded 50%. Students began to understand that no matter how many times you flip the coin, they had a 50/50 chance to get heads.
Sample of Student Work:Creating the "X" Cats #3 - Students enjoyed creating a model of their cats that represented the x-inactivation to provide a visual of one X chromosome being turned off while the other was being expressed.
As a kinesthetic review for students to work with traits associated with human genetics, the students will participate in a class competition of Human Genetics Bingo.
- Students will fold their paper into 1/3's and then into 1/3's again so then when it is unfolded the paper will contain 9 boxes.
- Students will brainstorm physical traits that they can observe in their classmates. Some student-generated examples may include:
- Freckles - No freckles
- Hitchhiker's thumb - No hitchhiker's thumb
- Widow's peak - No widow's peak
- Dimples - No dimples
- Cleft chin - No cleft chin
- Attached earlobes - Unattached (dangling) earlobes
- PTC paper taster - Non-PTC paper taster
- Brown hair - Blonde hair - Black hair - Red hair
- Brown eyes - Blue eyes - Green eyes - Hazel eyes
3. Students will select 9 of the traits and write one trait in each of the 9 boxes of their folded paper.
4. Once students have prepared their Genetics BINGO card, the fun begins! Students will ask their peers to sign their BINGO card if that peer expresses the phenotype that is named on the selected square. Students are not allowed to just give their paper to their peers and expect them to sign it. Students must work on their communication skills as well as their understanding of Biology.
5. Make the game as exciting as you want . . . think of prizes!!!
Student Work: Genetics BINGO Cards - Students each made their own unique BINGO cards based on the list of single gene traits that were brainstormed in the list above. Students worked to fill out their cards until a student in the class achieved "blackout" and filled their card.