OMG! Who's genes are you wearing?
Lesson 10 of 16
Objective: Students will be able to apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.
Warm-Up: What characteristics (traits) did you get from either of your biological parents?
This question is a sure way to get students engaged as many of them will want to share information about what trait they feel they inherited from whom. After allowing students to share with the class for a minute or so, I like to share a picture of my family so that the students will be able to learn a little about me, as well as see genetic variation in in the different physical appearances of my offspring and siblings. Point out that families don’t always share outward physical traits that suggest that they are related. Ask students to explain why they think this is so. Listen to their thoughts to gain a sense of their knowledge about inheritance and to surface any misconceptions that might exist within the class about hereditary.
This question sets the stage for the lesson on genetics by activating prior knowledge about the nature of the inheritance of traits.
Introduce New Material
Inform students of the learning targets:
- I can explain the difference between phenotypes and genotypes.
- I can use a Punnett square to calculate the probability of the inheritance of traits.
Introduce the vocabulary associated with the lesson: heredity, traits, characteristics, gene, allele, variation, homozygous, heterozygous, inheritance, genotype, phenotype, dominant, recessive, probability, monohybrid.
Instruct students to add bolded terms to their vocabulary maps. Remind them that the bolded terms have Greek or Latin root words, prefixes or suffixes. This is a vocabulary-rich lesson so plan to spend extra time explicitly teaching the vocabulary associated with the lesson at the appropriate times within the lesson. Students often struggle to use and understand the vocabulary of genetics correctly.Begin the lesson
with the music video,
Before viewing the video, establish the viewing purpose by telling students that they should know at the end of the video. Display the question they should consider while viewing:
- What traits did you see at the end of the video?
After viewing the video, ask students to respond to the question. Expect that student interest and willingness to respond will be high after viewing the video. Expect that students will identify things like blond hair, black hair, brown eyes, blue eyes, etc.. as traits. Don’t spend time clarifying the difference between traits and versions of traits at this point. The main purpose of the use of the video is to serves as a reference later in the lesson to help students solidify the concept of what is trait and what is a version of a trait.
Distribute guided notes or use a note-taking format that has been taught.
Begin by explicitly teaching the term, trait. Because students can struggle with the concept that traits are controlled by more than gene, spend time discussing the fact that two versions of a gene are needed for the expression of a trait. Introduce the term, allele. Explain that gene and allele are interchangeable terms. Reference the Meiosis, part 1 lesson to remind students that an egg or sperm carries only one allele for each inherited trait because allele pairs separate during meiosis.
Teach students that alleles are expressed as letters. Make an association between the letter “l” in letters and the 3 letter “l’s” in the word alleles to help students remember that versions of alleles (genes) are written as letters. Memory Cue: see alleles, think letters.
Reference the “Black or White” video. Ask student to think about the question that was asked earlier after they watched the video. Ask them to answer the same question again now that they understand the term, trait. Listen to their responses to assess how well they understand the subtlety of trait and versions of traits. Look for students to indicate that hair color is the trait and blond or brown hair is the version of the trait.
Once it is established that students understand the term, allele, introduce the term genotype. Ask students to look within the term and identify what word is within the term. Students should note that gene is found within the term, genotype. Explain that the genotype is expressed as letters, now known as alleles. Emphasize that the genotype is “worn” but not seen on the outside.
Display a check for understanding and instruct students to talk at their tables to determine to answers to the following questions for this scenario: a female homozygous black fur rabbit breeds with a male heterozygous black fur rabbit.
- What is the trait?
- Select an allele (one letter) to represent the trait.
- How many versions of the trait are described?
- What are the genotypes of the parents?
Contrast the term, genotype with the term, phenotype. Tell students to think of physical appearance when they see the term, phenotype. Make the connection between ph- of the word, phenotype and the ph- of the word, physical appearance. Emphasize that the genotype isn't seen but it determines the phenotype, which is seen. Give students a memory cue to remember the relationship between genotypes and phenotypes: The letters (genotype) determine the look (phenotype).
Have students repeat this statement after you 2-3 times.
Lastly, explicitly teach the difference between heterozygous and homozygous, referencing the root words in both terms to help students see that each word’s meaning is easily identifiable when the root words are known. Conduct a 2nd check for understanding. Display a set of alleles and ask the class chorally to indicate if the allele pair is heterozygous or homozygous.
Ask students, “ How many traits are crossed in a monohybrid cross?” If needed, guide them to the correct understanding by reminding them to identify the meaning of the prefix mono-. Look for students to identify that mono-means one. Ask what other words use this prefix. Allow students to share words that use mono and be prepared to share a few words as well (carbon monoxide, monolithic, etc…)
Use a LCD projector to display a monohybrid cross problem. Model the steps for completing a monohybrid cross using the think aloud strategy. Instruct students to follow along, using the guided notes to record the problem as it is calculated.
Distribute whiteboards and dry erase markers. Display a second Practice problem. But this time, instruct students to work in pairs to complete the problem and raise their board to show their answer before you model the calculation. This quick formative assessment will help identify if re-teaching is needed or not. As noted from the work, these students understand how to complete a Punnett Square.
Display a 3rd practice problem. Again, instruct students to work in pairs to complete the problem and raise their board to show their answer before you model the calculation. Observe which groups appear to understand how to perform a monohybrid cross and identify those that will need intervention during Independent Practice.
Distribute a set of Punnett square practice problems. Inform students that they will have to use the phenotypic descriptions and the chart of dominant and recessive alleles to determine the parental genotypes before they can complete the problems.
Assign all or a portion of the problems. Make sure that students know to include both the genotypic and phenotypic percentages in their answers. Use the information gained from the Guided Practice to identify which students will benefit from small group re-teaching, if needed. Re-teach concepts to the small group and release other students to work independently (or in paired groups) to complete the assignment.
Allow students to work independently (working solo or with assistance) for 10 or more minutes. Walk around to make sure that students are able to identify the correct genotypes of the parents. Encourage students to draw pictures or diagrams that will help them represent the parents phenotypes if they find themselves struggling to identify genotypes and work backward into the parents genotypes, using the legend.
Expect that some students will struggle to differentiate between geneotype and phenotype. Recall that the term, genotype refers to the gene (what you cannot see) and the phenotype refers to the physical features (what you can see). By dramatic and really emphasis pheno- as in physical features. Overly emphasizing pheno- will help some students remember that phenotype represents physical features.
The student work demonstrate that students did meet the learning targets for the lesson.
As a ticket out the door, display a chart with two columns, labeled Genotype and Phenotype. Work as a whole group to place each of the terms in each of the following pairs in the correct column:
- Hair color, brown hair
- Low cholesterol, cholesterol level
- Flower color, purple flower
- Plant height, tall plant
- Long tail, tail length
Distribute post-it notes and instruct students to use the “Parking Lot” to post any unanswered questions they may have about genes, alleles, traits, phenotypes and genotypes.