Sex-linked Genes

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Objective

Students will be able to explain how genes located on sex chromosomes have different probability of inheritance than genes on autosomal chromosomes

Big Idea

Does a sex matter in terms of how a trait is inherited?

NGSS

In this lesson students continue to grow in their understanding of several Disciplinary Core Ideas:

  • LS3.A: Inheritance of Traits – Each chromosome consists of a single very long DNA molecule, and each gene on the chromosome is a particular segment of that DNA. The instructions for forming species' characteristics are carried in DNA.

  • LS3.B: Variation of Traits – In sexual reproduction, meiosis can create new genetic combinations and thus more genetic variation.

Students will engage in several Scientific Practices – (SP2) developing and using models; (SP4) analyzing and interpreting data; (SP6) constructing explanations; (SP7) collaborating with peers and defending explanations; (SP8) engaging in discussions with scientific peers.

As students work to discuss their answers and determine the correlation between sex-linked genes and traits expressed, they explore the cross cutting concept Systems and System Models -"Models are limited in that they only represent certain aspects of the system under study". 

Hook

5 minutes

To start this lesson and get students excited, I play an introduction sequence clip from the popular show "The Simpsons".

Students will practice identifying sex-linked traits using these characters as the back story, so they get really excited about the lesson.

Explain

20 minutes

I use this slideshow to present the concepts. 

Once we have gone over the presentation, I ask the students to make a list of key ideas they took from the presentation and write them on post it notes that they can add to the concept map they created in The Tour the Basics lesson. This check allows the students to discuss their ideas (SP8), and gives them an opportunity for the authentic movement and conversation needed after hearing me talk for such a long period of time.

Practice

25 minutes

I tell the students that they will be practicing what they learned by uncovering the genetic probability of sex-linked traits in the Simpson's household, and distribute the Sex-linked Traits with Homer and Marge worksheet (answer key).

Students work on this sheet with a Clock-Buddy to relieve the monotony of working with the same people, and allowing them the opportunity to defend their explanations (SP7) as they engage in scientific discussions with their classmates (SP8).

The worksheet specifically asks them to draw conclusions from several Punnett squares as well as from the information provided (SP4). Take a look at the student work, and then watch as students give explanations, and share their understanding. Both of these provide me with evidence of student thinking, and let me know whether students have understood the concepts being presented and practiced. 

Closure

5 minutes

Students seldom complete the practice sheet before the time period ends, so in this case, I announce that whatever work was not finished will have to be completed for homework, and that I will collect it the next time we meet. 

I ask the students that any "burning" questions regarding the work be posted on Edmodo in order to be able to address them and have all students complete the work on time.