A Recipe for Traits
Lesson 11 of 19
Objective: SWBAT explain how DNA is a set of instructions that specifies the traits of an organism.
This lesson is part of a heredity unit that look at the inheritance and variation of traits. This lesson specifically looks at the mechanism behind how sexual reproduction results in the combination of two distinct pieces of DNA to create a unique individual. This mechanism results in the inheritance and variation of traits.
Performance Task Addressed:
MS-LS3-2. 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.
Science and Engineering Practices:
SP7: Engaging in Argument from Evidence
SP2: Developing and using Models
Cause and Effect: Cause and effect relationships may be used to predict phenomena in natural systems.
To engage in students in the lesson I show the The Story of Fido's Traits video which discusses the relationship between DNA and inheritance of physical traits. (MS-LS3-2-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.)
While students watch video I have students answer the following questions:
1) All dogs descended from what common ancestor?
2) All dogs are a result of how many pieces of DNA?
3) What is the reason why there is variation amongst siblings?
4) Siblings are only what percentage genetically identical?
5) What are the segments of DNA called?
6) What are some example of traits that are inherited?
7) Dominant traits only require ____ copy of each gene. What is the dominant color for dogs?
8) Recessive traits require ______ copies of each gene. What are some recessive colors for dogs?
9) What is the function of dog's melanocytes?
10) What type of hair is recessive? What type is dominant?
In this section we explore the relationship between DNA, genes, and traits by completing an activity titled Traits Recipe from Genetic Science Learning Center.
Students create and decode a “DNA recipe” for man’s best friend to observe how variations in DNA lead to the inheritance of different traits. Strips of paper (representing DNA) are randomly selected and used to assemble a DNA molecule. Students read the DNA recipe to create a drawing of their pet, and compare it with others in the class to note similarities and differences. (SP2- Developing and Using Models/MS-LS3-2 - 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.)
- Every organism inherits a unique combination of traits.
- DNA is a set of instructions that specifies the traits of an organism.
- Information in the DNA molecule is divided into segments (called genes).
- Variations in the DNA lead to the inheritance of different traits.
- Drawing Paper
- Colored Pencils
- Colored Paper for DNA strips (4 colors needed)
- Make sure to create envelopes with strips of DNA ahead of time.
- Ensure that students place strips back in envelopes after activity has been completed, one class set is sufficient to repeat activity.
- Explain to students that 4 symbols represented in strips are analogous to 4 type of chemical bases found in DNA. This is building background knowledge for future lessons.
- Students work in pairs to complete the activity.
1. Once all students have completed their drawings of their dogs ask them if any dogs are identical. Emphasize the point that variation in traits arose from different combinations of just four symbols, just as in DNA.
In this section of lesson students read a cK-12 article that explains the relationship between DNA, Chromosomes, and Gene expression. This article provides an explanation to the explore activity where a DNA recipe resulted in the expression of various genetic traits.
Topics Covered in Article:
- Autosomes vs Sex Chromosomes
- Alleles and Genetic Variation
Once students finish reading article students complete the following questions:
- Describe human chromosomes.
- Compare and contrast human autosomes and sex chromosomes.
- What is SRY?
- Why are females the "default sex" of the human species?
Teacher Note: I have included a Study Guide that explains DNA, chromosomes, and genes further.
This section of lesson elaborates on what students have learned about DNA and trait expression by learning about something that students are drawn to, bringing back Dinosaurs to life.
There's More than One way to Make a Dinosaur
The movie and novel Jurassic Park set people's mind a flutter with possibilities. Dinosaurs! Cloned dinosaurs from ancient DNA! How cool is that! Unfortunately, science has poured some cold water on this cool idea. It seems DNA doesn't stick around for millions of years, even under the best conditions it seems to be readable for only around 1.5 million years. Not much use in trying to bring back animals that disappeared over 65 million years ago. Read DNA Half Life to find out more.
Students use the Writing in the Margins strategy to help them tackle this scientific text.
Writing in the margins engages readers in the reading task and allows them to document their thinking while reading. Both writing in the margins and drawing in the margins engages students in actively thinking about the texts they read. The power of this strategy is not the actual act of writing and drawing in the margins; instead, it is the thinking processes that students must undergo in order to produce such ideas.
For this article students use the Clarify Strategy:
Clarify complex ideas presented in the text. Readers clarify ideas through a process of analysis, synthesis and evaluation. Pausing to clarify ideas will increase your understanding of the ideas in the text.
In order to clarify information you might...
define key terms.
reread sections of the text.
analyze or connect ideas in the text.
paraphrase or summarize ideas.
But all is not lost for those hoping for the dinosaurs return. Actually, as some of you know, they never really went away. Oh, the Age of the Dinosaurs ended and with it their world dominance, and most of them certainly disappeared. But some survived...we call them birds, and scientists like Jack Horner think they may be key to some very interesting science.
In this section of lesson students complete an Exit Slip that assesses their mastery of lesson's learning objectives. In this exit slip students are given the choice of completing 1 out of 3 prompts where they are required to write an evidence based argument. (W.7.1 - Write arguments to support claims with clear reasons and relevant evidence/SP7 - Engaging in argument from evidence).