Reflection: Grappling with Complexity Selective Pressure Happens! - Section 4: Partner Activity: Mapping the Family Genes


I had a group of students that decided they wanted to do a genetic cross with five different traits.  I tried to persuade them against it, but they were determined. I suggested that they use a spreadsheet program so that they could keep their Punnett square neat and less confusing.  Unfortunately, this group's work does not have all of the gamete possibilities for a five trait cross. A five trait cross should have 32 possibilities and their genetic cross group had ten. This is actually a very common mistake that students make.  As a teacher, it is important to do two things.  Show them the math so they can understand how the number of possibilities is determined.  Secondly, encourage them to set the Punnett square aside and continue with the lesson.  

First, I showed this group the reasoning that helped determine the number of possibilities.  It was a great connection between what students had learned in their math class and how it applies to genetic crosses.  I made a copy of this sheet and had them put it in their lab notebooks the following day.    

Next, I encouraged them to put the Punnett square aside because they had a good understanding of how it worked as a model. They were just bogged down in the details.  I told them to move onto the next part of the lesson where they picked one offspring from the second and third generation and made models.  This gave students a visual representation of the apparent "loss" of recessive traits in the second generation and the "reappearance" of those recessive traits in the third generation.  This was the entire purpose of this exercise.  It was more important for those students to understand this big idea than to get everything correct in their Punnett square.  

  Grappling with Complexity: Modeling Genetic Crosses
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Selective Pressure Happens!

Unit 13: Mendellian Genetics
Lesson 1 of 2

Objective: Students will apply laws of Mendelian inheritance to predict the genotype and phenotype of progeny. Students will also determine the effects of selective pressure on progeny.

Big Idea: Genetics isn't the only thing that can affect what offspring live to reproduce.

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1 teacher likes this lesson
inheritance (Biology), Science, cause and effect, Analyzing and interpreting data, Engaging in argument from evidence , genetic variation, Selective pressure, trait, Variation in Traits, Scale, proportion, and quantity
  80 minutes
screen shot 2015 09 01 at 10 02 44 pm
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