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Middle School Science: Genetics and the Law of Segregation

written by: Kathy Foust • edited by: Donna Cosmato • updated: 9/13/2012

This back-to-school science lesson plan turns genetics terminology into a language that can easily be understood by your middle school students as they begin their exploration of genetics.

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    Mendel's Law

    As students head back to school, this science lesson teaches students about one of the most basic laws of genetics. Students must learn about the law in this genetics lesson plan as an introduction to the generic topic of genetics.

    Introduce Mendel's Law of Segregation as follows:

    • Each individual has two factors for each trait.
    • The factors segregate as the gametes form.
    • Each gamete has only one factor from each pair of factors.
    • Fertilization gives each new individual two factors for each trait.

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    Genetics Activity

    Students are probably aware on some level that their parents handed down traits to them. They just don't know the specifics of how this happens. Have them create a list of some of their physical traits as well as a record of which parent they share those traits with. They will also have some traits listed and marked "other," meaning they are not aware of who they share this trait with. For this lesson students will focus on the traits that they marked as "other."

    • Ask the students how they got those traits if their genetics come solely from their parents.

    Use the Law of Segregation to explain that their parents also got one trait from each of their own parents and so on down the line. That's why a child with blue eyes may actually have parents who each have brown eyes or something similar. In order for the students to find out exactly where they got the traits that they don't recognize as their parents' traits, they would have to trace their own ancestry. Ask students to complete their sheets by considering the traits of their grandparents or even their great-grandparents.

    Use the scenario below as an example to explain the Law of Segregation.

    Jill and Tom each have blue eyes. They have a child with green eyes. Jill's mother has green eyes, as does Tom's father. Jill and Tom each carry the gene for green eyes, but that was not their dominant eye color gene. However, since each parent contributes their own gene and they both happened to contribute the recessive gene for green eyes to their child, the child ended up with green eyes.

    Review this information with students and ask them to come up with their own examples that explain how genes can seem to "skip" a generation.