Inheritance Patterns (#3 of 6): Codominance

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1. Students will apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population. (HS-LS-3) 2. Students will understand that cells store and use genetic information to guide their functions. An organism’s genotype determines its phenotype. These traits can be dominant or recessive depending on the alleles found on their genes.

Big Idea

Nearly all human traits, even many diseases, are inherited in predictable ways. Using the tools of mathematics and modeling, these inheritance patterns can be properly deduced.

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these. Furthermore, for the bigger picture of this unit of study please refer to this document.

With regard to this particular lesson (as part of the series) students will be able to...

1. Explain how are traits passed from one generation to another and why do members of the same family have different traits.

2. Explain why some traits are hidden in one generation and expressed in the next.

3. Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population. (HS-LS-3)

4. Solve monohybrid (one trait) and dihybrid (two trait) cross problems (AKA Punnett Squares).

a)    Complete dominance (click here to link to lesson)

b)    Incomplete dominance (click here to link to lesson)

c)    Co-dominance (e.g. ABO blood types) (focus of this lesson)

d)    Sex-linked (e.g. colorblindness and hemophilia) (click here to link to lesson)

5. Interpret a pedigree and the symbols used to represent males, females, affected and unaffected individuals. (click here to link to lesson)

6. Make and defend a claim for the inheritance pattern(s) found in a given pedigree. (click here to link to lesson)

I hope you get some value from my work!

Anticipatory Set ("Hook")

10 minutes

Teaching Challenge: How do I develop a classroom culture where students engage in meaningful and productive scientific discourse with peers?

Teaching Challenge: How can I develop a classroom culture that encourages student engagement, curiosity, and a desire to understand the world through scientific exploration?  

Blood Type Discussion

I don't know your perspective but blood typing always is a fascinating, yet poorly understood, topic for my students. It is important from a medical perspective for sure. And in the case of Japanese culture, blood type can be a discriminating trait. Type A blood (which, of course, I happen to be) is regarded as the premier blood type! However that belies a deep-seated misconception (from a medical standpoint at least); the only type that matters is that which is compatible with the individual who needs it. Therefore, I like to take advantage of this teachable moment and begin the lesson by discussing the basics of blood types (ABO blood groups, the RBC cell-surface sugars they represent, and the issues of blood type in-/compatibility and the value of Type O blood-to-blood banks). Invariably, students will ask questions that they wonder about such as:

"Which blood type is most common?" (Depends on the demographic in question)

"How can I learn my own blood type?" (I donated blood in college and requested the type so now I know)

"How does a blood transfusion work?" (Very delicately! Well, that wasn't my exact answer) =)

I had a student disclose that he has sold plasma to the blood bank from time to time and more than a few students' eyes lit up like they were thinking "CHA-ching!" which brought a lot of laughs from the class. I always try to be open to these kinds of illuminating moments. Quite memorable for sure!

I then have students compare and contrast the genotype system for co-dominance with the prior two patterns. They should note that there are two mutually independent ways to be “dominant” (AB) but one recessive form (O).

Instructional Input/Student Activities

35 minutes

Punnett Squares Practice packet (Co-dominance pp. 3-5)

As done before I work through problems #1, 2, and 4 together with students. I chose #4 additionally because it presents multiple layers of thinking as the solution is worked. In other words, the problem gets complicated with the presence of a non-biological (adopted child) in the mix. Thereafter, students will complete #3, 5-8 on their own.

As they do so, I roam the class checking that students are faithfully following the full process and being on hand to help students as needed. I offer extra credit for solving problems #1-6 on p. 5.

If necessary, the 7-step process is reviewed in this document.

Closure: What did we learn? Where do we go from here?

10 minutes

Formative assessment is crucial for getting that "dipstick" measurement of student learning. There are a great many ways in which this can be done. One of the more recent and very transformational strategies I have used is called the Peer Instruction Protocol first devised by Dr. Eric Mazur.

Peer Instruction Protocol (PIP) 

As a wrap-up for today, I conduct the review using the PIP assessment (only questions #5 & 6)