Human Genetic Variation
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Figure 1 - Humans are a genetically diverse lot. How will understanding this diversity at a molecular level change our lives?

Introduction

Human Genetic Variation has two central objectives. The first is to introduce students to major concepts related to human genetic variation. Homo sapiens comprises a single species, yet the more than 6 billion of us alive today, and the millions who preceded us following the emergence of fully modern humans some 150,000 years ago, are a diverse lot. One look at the students who sit in your class each day is all you need to confirm that fact. The module's first objective is to help students recognize and understand this variation.

The second objective is to convey to students the relationship between basic biomedical research and the improvement of personal and public health. The new knowledge that scientists are gaining as they map and sequence the human genome is rapidly changing the practice of medicine, and it is vital that citizens recognize these changes and are prepared to deal with them. Being prepared involves understanding the basic science that underlies new medical practices and therapies, and recognizing the complex issues and questions that some of these procedures and therapies raise. Thus, the module's second objective is to help students think about how the detailed analysis of human genetic variation is already changing their lives.

If recognizing human variation is common, it is not new; certainly our ancestors realized that no two humans are identical. Nevertheless, biologists before Charles Darwin subscribed to what Ernst Mayr has called "essentialist thinking": the notion that each species is defined by an invariant type that limits the ability of its members to vary too much from the essential nature of the species. Among Darwin's great insights was the recognition that the essentialist view is incorrect, that the members of any given species are highly variable, and that some variations within a species will confer selective advantage on those individuals that possess them. This variation within species makes differential selection, and therefore evolution, possible. Mayr has called this view "population thinking," and it pervades modern biology.

Darwin, however, even while working as Mendel's contemporary, was confounded by his inability to identify the root source of biological variation or the mechanisms by which those variations are transmitted to subsequent generations of organisms within the same species. The rediscovery of Mendel's work in the early 1900s provided those answers, and the reconciliation of Mendelism and Darwinism in the modern synthesis of evolution in the 1930s and 1940s formed the basis for the biology we practice and teach today.

The identification of DNA as the genetic material in the early 1940s, and the elucidation of its structure about a decade later, opened the way for an analysis of genetic variation at the molecular level. That analysis proceeds at breakneck speed today, propelled by a host of powerful new techniques in molecular biology.

This module focuses on our progress in analyzing human genetic variation and the impact of that analysis on individuals and society. There are many concepts we could have addressed, but we have chosen, with the help of a variety of experts in this field, a relatively small number for exploration by your students. Those concepts follow.

We hope the five activities provided in this module (Figure 2) will be effective vehicles to carry these concepts to your students. Although the activities contain much interesting information about various aspects of human genetics, we suggest that you focus your students' attention on the major concepts the module was designed to convey. The concluding steps in each activity are intended to focus the students' attention on those concepts as the activity draws to a close.

Figure 2 - This diagram identifies the module's major sections and describes their contents.
Activity 1
Alike, But Not the Same
Activity 2
The Meaning of Genetic Variation
Activity 3
Molecular Medicine Comes of Age
Activity 4
Are You Susceptible?
Activity 5
Making Decisions in the Face of Uncertainty
Students conduct an inventory of human traits and play a game that highlights each individual's uniqueness. Students investigate variation in the beta globin gene. Students assume the roles of employees of two fictional pharmaceutical companies to discover medical benefits of understanding variation at a molecular level. Students explore the relationship between genetic variation and environmental factors in the onset of heart disease. Students analyze a family's decisions about testing for variants of genes that increase susceptibility to breast cancer and consider some of the personal and social implications of genetic testing.
 

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