1. Topic-
Probability and Heredity
 
2. Content-
Key Terms:

probability
Punnett square
phenotype
genotype
homozygous
heterozygous
codominance
 
3. Goals: Aims/Outcomes-
1. Explain that Mendel used the principles of probability to explain his results.
2. Recognize how probability is used to predict what will possibly occur, but not what is definitely occur.
3. Apply the principles of probability to predict genetic crosses.
 
4. Objectives-
1. Define probability and describe how it helps explain the results of genetic crosses.
2. Explain what is meant by genotype and phenotype.
3. Develop hypotheses about whether traits controlled by dominant alleles are more common than traits controlled by recessive alleles.
 
5. Materials and Aids-
Science Explorer: Prentice Hall Life Science:
Prentice Hall (2009). Science Explorer: Life Science. (Teacher's Edition). Upper Saddle River, NJ: Pearson. Print.
Discovery Education, United Streaming website
NSTA: SciLinks.org
Phschool.com
Smartboard
PowerPoint
Responders
Internet
 
6. Procedures/Methods-

A. Introduction-

1. Explain that knowing the definitions of key-concept words helps students understand what they read.
2. Have students write the key term definitions in their own words.
3. Call on volunteers to read their definitions aloud. Make sure that students have explained the definitions in their own words.
4. Invite students to describe situations in which they have used a coin toss to decide an issue. Ask the students, "Why did you toss a coin in these situations?" and "Why is a coin toss fair?"
 

B. Development-

How to Make and Interpret a Punnett Square:
1. Display a blank Punnett square on the Smartboard and explain why it is broken into four squares.
2. Write the male parent's alleles along the top of the square and the female parent's alleles along the left side.
3. Copy the female parent's alleles into the boxes beneath them.
4. Copy the male parent's alleles into the boxes beneath them.
5. The completed Punnett square shows all the possible allele combinations in the offspring.
6. Describe the genotypes and phenotypes of the offspring.
 

C. Practice-

1. Remind the students that a Punnett square identifies possible gene combinations.
2. Have students divide into small groups and identify the alleles that each could pass on to the offspring (BB and bb.
3. Circulate the classroom to make sure students understand how the alleles combine.
4. Ask the students, "Why are all the offspring black?". (Black is the dominant allele, and all the offspring have it.)
5. Ask the students to apply the principles of probability by asking, "What percent of the F2 generation of offspring are likely to be black and why?" (75%)
 

D. Independent Practice-

1. Analyze and interpret the data in a bar graph reflecting the results of Mendel's pea plant crosses.
2. Identify the data plotted on the x-axis and y-axis.
3. Read the graph to determine how many F1 offspring have yellow seeds, how many had green seeds.
4.Calculate the total number of offspring that resulted from this cross. Then calculate the percentage of the offspring with yellow peas, and the percentage with green peas.
5. Use calculations from number 4 to infer probable genotypes of the parent plants.
 

E. Accommodations (Differentiated Instruction)-

1. Provide one student in a pair with four straws of different lengths, but all the same color.
2. Ask the student to hold them so that they all appear to be the same length and ask them, "What is the chance that the longest straw will be chosen?" (one out of four)
3. Have the second student in the pair replace the straw. Ask if the probability is still 25% that the same straw will be chosen if he or she draws again.
4. Explain that this models how the events occur independently and how we use the Punnett square to model this as well.
5. Have students repeat this exercise as needed to understand the concept.
 

F. Checking for understanding-

1. Display the section 2 assessment questions from page 123 of the text on the Smartboard.
2. Have the students use the responders to answer each question using multiple-choice options. This data will be saved for later analysis and interpretation so teacher can differentiate and revise instruction based on individual student needs.
3. Stop after each question, explain, discuss, and reteach if necessary.
 

G. Closure-

1. Review the principles of probability by discussing the Punnett squares on pages 120-121 and 123.
2. Review the key concepts of homozygous alleles, heterozygous alleles, as well as the codominance. 3. Remind students that capital letters are used to reflect dominant alleles, lowercase letters are used reflect recessive alleles, and capital letters are accompanied by superscripts to reflect codominance.
 
7. Evaluation-
1. Create a Punnett Square to predict the results of a genetic cross when the genotypes of both parents are known. (male parent brown eyes Bb and female parent blue eye bb). Have the students explain the results and provide the percentages of the probability of each cross for each offspring. Have the student predict the outcomes if the male parent was BB and the female was bb, then if the male was BB, and the female was Bb.
2. Administer section test with multiple-choice items, short, constructed-response items, and one essay. Mark and analyze the results to determine weaknesses as well strengths. Differentiate instruction and reteach if necessary.
 

This Lesson Plan is available at (www.teacherjet.com)