Modeling With Mendel
1 Hook: What are Purebred Dogs and How are They Related to Designer Dogs?
Begin by asking students what they know about purebred dogs. In the ensuing discussion, ideas should come up such as:
- A purebred dog comes from two parent dogs of the same breed.
- Purebred dogs must be recognized by the Amerian Kennel Club (AKC) or a similar organization.
- The dog's pedigree must be verified - generally through genetic testing.
- Purebred dogs are expensive.
- Purebred dogs often have health problems.
Introduce the idea of "Designer Dogs." These are created when two purebreds are mated to create a hybrid that
combines the desirable traits of each parent. Use the article that is linked to find a list of popular designer dogs.
You or your students can make up a game of “match the parents to the offspring.” Have each student print out
pictures of two parent dogs of different breeds, and a picture of their hybrid offspring. Pictures of both of these are linked in the article. Put each parent pair in a row on the wall, and place the offspring in random order below.
Challenge your students: Who can do the best job of matching parents to their offspring?
Discuss how students think the traits were inherited. Do all offspring from the same parents look the same?
- Students brainstorm in partners or completed a KWL about purebred dogs.
- Students read the article about "designer dogs"
- Students obtain pictures of purebred dogs and their designer offspring and match the offspring ot the parents.
- Students discuss how the "designer dogs" inherited the traits that make their appearance desirable to pet owners.
2 Direct Instruction with Interactives
Introduce genetics concepts through two interactives from PBS Learning Media, "What is Heredity?" and "What is a Trait?" Students may work individually or in pairs. Once a students logs into the site (the titles are linked) the directions and process is self-explanatory. Volume on the computers should be turned on.
- Students work independently or with a partner to complete the interactive web-based activity, "What is Heredity?"
Students work independently or with a partner to complete the interactive web-based activity, "What is a Trait?"
3 Guided Practice with Expl.oreLearning Gizmos
Distribute or make available online the Student Sheet for "Mouse Genetics (One Trait)." This simulation walks students through simple patterns of inheritance. Students may work individually or in pairs. Concepts addressed include:
- dominant allele
- Punnett square
- recessive allele
Besides the online assessment that students may take to check for understanding, the following discussion questions may be used to check for understanding:
- If two parents of the same color are bred together, do all of their offspring always have that color? (Which situation is an exception to that rule?)
- How do you know that the trait for white fur is still present in a black-fur hybrid?
- Why is it impossible to see a hybrid (or heterozygous) white mouse?
- A black mouse is bred to a white mouse, producing 2 black and 1 white offspring. What is the genotype of the black mouse?
- A black mouse is bred to a white mouse. They produce three black offspring. What is the genotype of the black parent? [Note: This is a trick question! The genotype of the black parent cannot be determined from this information, although as more black offspring are produced, the probability of FF increases.]
- An Ff mouse is bred repeatedly to an ff mouse, producing 500 total offspring. In theory, 250 offspring should be black and 250 should be white, but the actual numbers are 237 black and 263 white. Why does this happen?
- Follow the directions on the Student Sheet
- Be prepared to discuss the concepts that were addressed.
- At the end of the simulation, take the online assessment
4 Guided Practice by Close Reading of Text
To gain insight into how the patterns of inheritance were developed, have students read Gregor Mendel's biography, "Rocky Road: Gregor Mendel."
Additionally, students may read Mendel's original work, "Experiments in Plant Hybridization (1865).
Students can annotate and discuss one or both articles.
- Read the articles the teacher provides.
- Read each article a second time and
- Circle any words you do not understand
- Ask questions in the margins if there are concepts you do not understand
- Highlight important information that helps explain how the mice inherited traits from the last activity or how the "designer dogs" inherited the traits that made them desirable.
5 Independent Practice in Creating Punnett Squares
The above link provides more information and practice for students in drawing Punnett Squares.
- Review with a partner how to draw a Punnett Square.
- Using the link you teacher provides, draw additional Punnett Squares and discuss their value in making prediction about speciifc traits.
6 Independent Practice with more Punnet Sqaures ans well as other Inheritance Patters
The following Explore Learning Gizmos provide additional practice for students and reinforce the information previously presented.:
Distribute or make available the Students Sheets from the site and have students follow directions on them. Besides the online assessment that students may take to check for understanding, below are additional questions for discussion:
Discussion Questions for Inheritance:
- How is asexual reproduction different from sexual reproduction?
- Why aren’t acquired traits like tattoos passed from parent to offspring?
- Which alien trait is determined by its environment?
- Can alien parents with straight antenna produce offspring with curly antenna?
- Can alien parents with curly antenna produce offspring with straight antenna?
- How can a trait “skip a generation”?
Discussion Questions for Chicken Genetics:
- Which feather color is recessive: white or red? [The allele for neither of the feather colors is recessive. Both colors are controlled by dominant alleles.]
- Why does crossing a pure white chicken and a pure red chicken only produce mixed-colored offspring?
- Suppose two mixed-colored chickens were crossed and they produced a white feathered offspring. Could this offspring be heterozygous for red feathers?
- Suppose you were studying the inheritance pattern for fur color in rabbits. How could you determine whether rabbit fur color was a codominant trait?
- Do you think probability calculations predict average outcomes or exact outcomes?
For additional practice, use the Gizmos your teacher provides.
You should be able to explain the difference between sexual and asexual reproduction
You should be able to explain how the mechanism of co-dominance affects the inheritance of traits.
7 Wrap-up and Extend by looking at the INheritance of Two Traits
Use the Explore Learning Gizmo, Mouse Genetics (Two Traits). In this activity students:
- Explore inheritance of two traits.
- Use Punnett squares to model the inheritance of two traits and predict probabilities of each offspring’s allele combination.
- Use two Punnett squares to model each trait independently, then multiply the probabilities to find the probability of a given allele combination.
- Use a single 4×4 Punnett square to model the inheritance of two traits.
Besides the online assessment that students may take to check for understanding, below are additional questions for discussion:
- What is the genotype of a mouse with white fur and red eyes?
- What are the possible genotypes of a mouse with black fur and black eyes?
- Without looking at its genotype directly, how could you determine the genotype of a mouse with black fur and black eyes?
- Two Ff Ee mice are bred. What is the probability of an offspring with white fur and red eyes? [The odds are 1 in 16, or a 6.25% probability.]
- An ff Ee mouse is bred to an Ff Ee mouse. Determine the following probabilities:
- Black fur, black eyes. [3/8, 37.5%]
- Black fur, red eyes. [1/8, 12.5%]
- White fur, black eyes. [3/8, 37.5%]
- White fur, red eyes. [1/8, 12.5%]
Key Standards Supported
Cite specific textual evidence to support analysis of science and technical texts.
Determine the central ideas or conclusions of a text; provide an accurate summary of the text distinct from prior knowledge or opinions.
Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.
Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).
Distinguish among facts, reasoned judgment based on research findings, and speculation in a text.
Compare and contrast the information gained from experiments, simulations, video, or multimedia sources with that gained from reading a text on the same topic.
Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
Determine the central ideas or conclusions of a text; trace the text’s explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words.
Assess the extent to which the reasoning and evidence in a text support the author’s claim or a recommendation for solving a scientific or technical problem.
Compare and contrast findings presented in a text to those from other sources (including their own experiments), noting when the findings support or contradict previous explanations or accounts.
Cite specific textual evidence to support analysis of science and technical texts, attending to important distinctions the author makes and to any gaps or inconsistencies in the account.
Determine the central ideas or conclusions of a text; summarize complex concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms.
Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.
Integrate and evaluate multiple sources of information presented in diverse formats and media (e.g., quantitative data, video, multimedia) in order to address a question or solve a problem.
Evaluate the hypotheses, data, analysis, and conclusions in a science or technical text, verifying the data when possible and corroborating or challenging conclusions with other sources of information.
Synthesize information from a range of sources (e.g., texts, experiments, simulations) into a coherent understanding of a process, phenomenon, or concept, resolving conflicting information when possible.
Key Standards Supported
Heredity: Inheritance and Variation of Traits
Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.
Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.