Predicting Probability With Punnett Squares
Lesson 7 of 13
Objective: SWBAT predict the probability of a single trait cross by developing a punnett square to visualize the variation and distribution of a given trait.
The video clip introduction focuses on Punnett squares and highlights the main points which incorporate NGSS Life Science 3-3, as well as multiple science practices and the cross-cutting concepts of applying patterns to understand science concepts.
The value of this lesson is challenging students to apply what they have learned to develop their own genetics practice problem and create a Punnett square to determine the probability of the outcome.
Students will watch the video and record the vocabulary terms that are introduced through the presentation. Students should be comfortable with incorporating these genetic terms in their daily Biology discussion but it is important to review before the class progresses into Punnett squares and probability of genetics.
Basic Genetics Vocabulary:
- Punnett Squares
Students will turn to their partner and check for understanding. The older student will share a quick definition for each term. While the younger partner will provide an example that represent the term described by their partner.
Sample Student Definition: "Allele - a possible version of a gene (different flavors)"
Sample Student Example: "eye color - blue, brown, and green eyes are possible alleles (colors) that a baby will inherit."
Some of your students may have been introduced to the concept of Punnett squares in middle school life science, but many students do not remember how to develop a Punnett square to accurately predict the probability of a genetic cross.
It is important to remind your student that Punnett squares DO NOT TELL THE FUTURE! Punnett squares are a tool to organize the geneotypes of the parents for a given trait, create the cross, and count up the possible genotypes/phenotypes that can result for the given cross. The punnett square will not tell exactly what will occur, but will allow students to trace the genotypes of the parents, create potential genotypes of the offspring, and calculate the probability of the offspring occurring in the population.
Punnett squares are a simple tool for students to create that will organize their data and provide a visual representation of the distribution of certain traits. Although Punnett squares are useful tools to predict outcomes, many students view them as riddles as they work to calculate the probably outcomes.
As a simple introduction, or possible review, students will record Probability Punnett Squares Lecture Notes that describe how to create a Punnett square and the rationale of using Punnett squares to predict probable genetic outcomes. The lecture notes contain five review questions to reinforce the main idea of creating and solving Punnett square practice problems.
Students will work collaboratively to create their own punnett square to represent the genetic cross for the following trait:Bear Fur Color
Brown Fur - BB
Brown Fur - Bb
Black Fur - bb
- Partners will select the genotype of the mother and the genotype of the father.
- Partners will each draw their punnett square on their individual paper.
- Partners will cross the alleles by filling in the punnett square.
- Partners will calculate the genotypic and phenotypic ratio that represents the outcome of the genetic cross.
- Students will need to describe the outcome in a complete sentence.
- Example of a Conclusion Statement - When a homozygous brown bear (BB) is crossed with a homozygous black bear (bb), the outcome of the cross will be 100% heterozygous brown bear (Bb) offspring. Even though all of the bears have black fur, the brown fur allele is still there and can be expressed in the next generation. Writing the conclusion statement is a new strategy in my classroom this year in an attempt to provide more writing opportunities for students where they need to explain their answer by providing evidence of critical thinking.
Students are encouraged to use their lecture notes as a resource during this activity. The teacher will rotate around the room to mini-conference with the partners to informally assess student understanding.
Students will use the Introductory Genetics Practice Worksheet to reinforce their skill to set-up the Punnett square, complete the genetic cross, and most importantly calculate the probability of genotypic and phenotypic outcomes in the form of a ratio.
Sample of Student Work - Punnett Squares - This document demonstrates the student's satisfactory understanding of these introductory genetic concepts. The students has a strong grasp on the topic and is ready to advance to dihybrid crosses.
Additional Practice Activities: These additional reinforcement activities can be used to differentiate instruction to meet the needs of the diverse learners in your classroom.
Student Reflections: Students will reflect on their experiences in today's lesson by writing a statement that describes the value of using Punnett squares to predict the probability of outcomes and how these probabilities contribute to the variations that are observed in a population.
Student-Developed Practice Problems: Students will use the experience in today's lessons as a guide to develop their own genetics word problem that they will challenge their partner to solve as an anticipatory activity in the next lesson. In order to assess student comprehension, all students must solve their own problem and provide an explanation that discusses the outcome of the sample problem.
Students will complete the Reflection and Practice Problem as homework.
Punnett Square Student Reflection #1: This student has demonstrated an understanding of how to fill-out or complete a simple genetic cross using a Punnett Square. This student will need a short conference to ensure that she grasps that Punnett Squares do not provide the exact outcome, but provides the probability of an event occurring.
Punnett Square Student Reflection #2: This student has demonstrated a strong understanding of Punnett Squares and its ability to provide the probability of "different outcomes that you can get". This student appears to be ready to progress to more advanced lessons/activities that utilize simple Punnett Squares to predict the outcome of some very entertaining topics!