Finding a Gene on a Chromosome Map

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Objective

SWBAT be able to use a pedigree to explore how genetic scientists use family tree information to track genetic disorders

Big Idea

Which gene is causing the disorder in this family? Learn how geneticists examine DNA to locate a gene responsible for an inherited disorder.

The Need for the Lesson

Students often believe that humans have different genes. This lesson reinforces the fact that all humans have the same genes in the same order along our chromosomes. But we inherit different combinations of alleles which gives us our unique characteristics.

Middle school students need to have a real world connection to what they are learning. They are familiar with the use of DNA in criminal investigations. This lesson extends their thinking to look at inherited genetic disorders. In this lesson students will use a jigsaw model to work as geneticists to determine which gene is responsible for an inherited disorder. The model represents a simplified version of the DNA actually used in genetic research. The simply model allows students to experience the work in genetics without becoming overwhelmed.

Investigation Preparation & Summary

5 minutes

The Next Generation Science Standards (MS-LS3-1- Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.) and (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) do not mention DNA specifically. 

DNA is not mentioned specifically until high school. (HS-LS3-1 - Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring.)

Students see chromosomes in action when they learn about mitosis. The standards then leap to genes and genetic expressions. 

Most middle school students can tell you that DNA provides the information needed for traits. This lesson provides students with a closer look at DNA and the work done by geneticists.  Students will learn that DNA is a molecule with different sequences resulting in the diversity of life. Students will examine a jigsaw puzzle as a representative model of DNA to determine which gene is responsible for an inherited disease. (SP2 - Developing and Using Models)

Students are challenged to analyze the DNA samples and draw conclusions about the genetic make-up of individuals in a pedigree.

This lesson has minor modifications of the lesson found on the Genetic Science Learning Center website.

University of Utah. "Finding a Gene on the Chromosome Map" Teach Genetics. University of Utah, 2004. Web. 10 May 2015.

Students in Action

45 minutes

First I share an image of DNA that might be used in a forensic lab to compare samples taken at the crime scene. 

What does a forensic scientist do? A forensic scientist analyzes evidence from a crime scene to help find the criminals.

Here are some DNA samples being analyzed by a forensic scientist.

What do we see in the image on the left? Sample DNA from the crime scene, the victims DNA and the DNA of two possible suspects.

What are the forensic scientists looking for when they compare multiple samples of DNA? They are using the sample from the crime scene to see if it matches the victim, or one of the suspects.

Look at the image on the right, what did the forensics scientists discover? The DNA at the crime scene matches the DNA of Suspect 1.

How is it possible that the forensic scientist can compare the DNA samples and use them to determine who committed the crime? They are matching the samples.

I remind students that all humans have the same genes, arranged in the same order. We all have 23 pairs of chromosomes. But each of us has a unique combination of DNA. You inherit one allele from each of your parents. Our genes number about 20,000.

Sometimes DNA is mutated or altered. Think of a mutated gene as a typo where the typo causes instructions to be altered. It is a permanent change in DNA, making the DNA different than what is found in most people. Sometimes DNA is damaged by UV radiation, chemicals or even viruses.

Many time mutations cause no harm and may even go unnoticed. Other mutations simply make us unique and create diversity.

The genetic mutations we hear about most frequently are those that cause disorders. Color-blindness for instance is caused by the mutation of a single gene.

In this lesson we will work like geneticists to find a gene responsible for the Whirligig disorder. You have found a large family with several members having the disorder. This fictitious disorder causes those with the gene mutation to dance when they hear Rolling Stones songs.

To help you find the gene responsible for the disorder, you will use a tool called a pedigree. The pedigree describes family relationships and show which family members have been diagnosed with the disorder. This pedigree is color coded and includes a key. The pedigree you are using for this lesson identifies the individuals with the Whirligig mutation. Pedigrees may be presented with slight differences but there are standards. Males are always represented as squares and females are represented with circles. I use this image to help students see the relationships; mother/father, children/spouses and siblings. Doctors and scientists use pedigrees to show relationships among family members and show which family members are affected or unaffected by the gene mutation.

Since this is a fictitious disorder, we will not be looking at actual DNA samples. The DNA you are analyzing is in the form of a jigsaw puzzle. 

You will use the information in the pedigree to identify the color and number of the puzzle piece representing the gene responsible for the disorder. 

Read through the instructions on pages 1 and 2, then answer questions 1 and 2 on the third page.'

I circulate around the room as students are working with their elbow partners to determine which gene is responsible for the Whirligig disorder, helping students develop a strategy if they are stuck. Most students dig right in.

This portion of the lesson takes about 15 minutes. I challenge early finishes to go ahead and tackle the remaining questions on page 3.

When all students are finished with questions 1 and 2, we break for a quick check in to share what we discovered. Students note that puzzle piece #36 is responsible for the Whirligig disorder. All affected family members have a red puzzle piece #36. We note that Whirligig disorder is autosomal dominate. We know it is dominate because it does not skip a generation and it in not a sex-linked gene because it affect males and females equally.

As students progress into the next questions, I remind them of a previous lesson.

In Genetics - Introduction to Punnett Squares, we learned about Mendel and his experiments with genetic variations of peas.

I remind students that Mendel crossed a yellow pea plant with a green pea plant and was surprised to find the next generation had only yellow peas. When he crossed the second generation, he found that some of the third generation peas were green. This led him to conclude that yellow was the dominate gene and green was recessive. In order to answer the remaining questions, you will need to take a look at more than one generation.

Questions 3 - 6 were difficult for several of my students. In this video, I explain my strategy for modeling how to find the answers.

The teacher answer key from the University of Utah Teach Genetics site has detailed explanations of the solutions for the remaining questions. In the short video below, you will see a sample of student work and see the notations made to help answer the questions.

Connecting the Learning

5 minutes

In the final few minutes of the lesson, I ask student to open their science journal and reflect upon this questions.

What are the consequences of knowing or not knowing that someone has a genetic disorder? Would you want to know if you had a genetic disorder that could be harmful in the future?

Student responses vary. It is a good reflective questions Just because we have the technology, does it make sense to use it?