Lesson 1A-3: Genetic Variation and the Malaria-Sickle Cell Link

Engaging the Student (Entry Task) 

Checking for Understanding (exit ticket)

2 class periods

 Briefly review prerequisite knowledge of genetics, inheritance and natural selection.

Ask students:

1. What is the ultimate source of all new genetic traits?
2. Are all genetic mutations adverse or unfavorable? Give an example to support your answer. 

Student Handouts

Contents: 

• Page 1: How Much Variation? Beta Globin Gene (Person A)

•  Page 2: How Much Variation? Beta Globin Gene (Person B)

• Page 3: How Much Variation? Doing the Math

• Page 4: Exploring Sickle Cell Disease

• Pages 5 & 6: Hard-copy of Reference Database (if internet unavailable)

• Page 7: Results of the Lindsey Test 

View the full 2-day lesson plan here:

• Lesson 1A-3: Genetic Variation and the Malaria-Sickle Cell Link

To prepare for this lesson, please read this:

• Teacher Guide: Understanding Human Genetic Variation 

In this lesson, students investigate variation in the beta globin gene by identifying base changes that do and do not alter function, and by using several Internet-based resources to consider the significance in different environments of the base change associated with sickle cell disease.

As discussed in the Teacher Guide: Understanding Human Genetic Variation, there is considerable variation between the genomes of any two individuals, but only a small amount of that variation appears to have any significant biological impact, that is, produces differences in function. The Human Genome Project will continue to illuminate the extent of human genetic variation as well as the variations that have biological significance.

This activity uses an examination of variation in a 1,691-base segment of the beta globin gene to help students consider the extent of human genetic variation at the molecular level and the relationships between genetic variation and disease and between genetic variation and evolution.

Major Concepts: The ultimate source of genetic variation is differences in DNA sequences. Most of those genetic differences do not affect how individuals function. Some genetic variation, however, is associated with disease, and some improves the ability of the species to survive changes in the environment. Genetic variation, therefore, is the basis for evolution by natural selection.

Objectives: After completing this activity, students will:

• recognize that the extent of molecular variation between two people is only about 0.1 percent, but because of the large size of the human genome, this translates to about 3 million base differences;
• understand that most human genetic variation does not appear to affect function;
• be able to explain that some human genetic variation is related to disease and provide an example; and
• be able to describe a benefit of human genetic variation and relate this benefit to human evolution by natural selection.

Prerequisite Knowledge: Students should understand basic Mendelian patterns of inheritance, especially autosomal-recessive inheritance; the basic structure of DNA; the transcription of DNA to messenger RNA; and the translation of messenger RNA to protein.

Basic Science-Health Connection: Although the idea is made explicit only in annotations to teachers, this activity illustrates how advances in science and technology have allowed us to establish relationships between some genetic variations and particular phenotypes. For example, our understanding of the relationship between DNA and protein has allowed us to establish a relationship between a change in a single base pair and the symptomology of sickle cell disease. Similarly, our understanding of the basic biochemical mechanisms underlying the symptoms associated with sickle cell disease has provided important clues about possible strategies for clinical intervention. You may wish to make some of these points with your students as they complete the activity.

Copyright ©1999 by the BSCS and Videodiscovery, Inc. All rights reserved. You have the permission of BSCS and Videodiscovery, Inc. to reproduce items in this module for your classroom use. 

• Copies of Student Handouts Pages 1-4 , one copy per student
• Copies of Student Handout Page 7, one copy per team
• Copies of Student Handout Pages 5-6 (if internet research unavailable) 
• Computer with Internet Access (1 per team)
• Web Resource Links:
• Mini-Documentary: What is Sickle Cell Disease?
• Online Reference Database 

Teachers, see full lesson plan for exit ticket answers. 

1. Will natural selection favor the survival of people who produce Hb S or people who produce normal hemoglobin?
2.  All populations have genetic variations that lead to increased incidence of particular disorders (for example, cystic fibrosis among Caucasians of European ancestry, Tay-Sachs disease among Eastern-European Jews, and a particular type of Thalassemia, a blood disorder among Asians). Explain why such apparently harmful variations have been maintained in those populations.