HUMAN GENETICS

for 1st YEAR STUDENTS


INTRODUCTION

Organization of the Course

T his course will cover the classical portions of human genetics required of all first year medical students at UIC. It is designed as a series of topics or review sessions with multiple choice questions for review and understanding. An instructor will be available for specific questions via E-mail. Contact the course coordinator for E-mail addresses. The course is not designed to be comprehensive in scope, but has been edited to cover selected topics considered most important to the practice of medicine by the American Society of Human Genetics at a level that the Department of Molecular Genetics feels is sufficient for first year students. Portions of human genetics will be covered in other basic medical science courses and, of course, all areas will be expanded during the clinical years. Human genetics is the most rapidly expanding area of medicine and, without serious editing, could easily consume the entire medical curriculum.


Required and Optional Texts

It is assumed that all students taking this course for credit will have access to Principles of Medical Genetics, 2nd Edition by Thomas D. Gelehrter, Francis S. Collins, and David Ginsburg. This is a required text and should be available in the bookstore. You will be responsible for any material in this text. Those of you who have had a formal course in genetics or human genetics, and just need to review basic material, may wish to use The National Medical Series for Independent Study, Genetics, by Jan M. Friedman, Fred J. Dill, Michael R. Hayden, and Barbara C, McGillivary (National Medical Series from Williams & Wilkins) Harwal Publishing Company, Malvern, Pennsylvania as an alternative to this computer-based course. Those of you who have not had a formal course in genetics may want to begin with a basic text in genetics, such as Genetics, 3rd Edition by Daniel L. Hartl, Jones and Bartlett Publishers, Boston, or Genetics, 3rd Edition by Peter J. Russell, Harper Collins Publishers, New York, or a similar recent text before attempting the study of human genetics. The choice of learning styles is up to each individual student, as it will be throughout your medical career.


General Introduction

Human Genetics has many areas of expertise, with specialists in each area. This course will focus on four areas, classical or Mendelian genetics, diseases where major effects are from a single locus, multifactorial inheritance, continuous traits (height, intelligence, etc.) and discontinuous traits (pyloric stenosis, cleft palate, etc.) where several genes plus environmental factors are involved, cytogenetics, diseases involving chromosomal abnormalities, and mathematical genetics, including population genetics, linkage, and mapping. Molecular genetics, the most rapidly developing of the genetic fields will be covered in the lecture portion of BMS 655, Human Genetics. Even at the basic level molecular genetics is changing too rapidly to be included in this computer-based course. All of these areas of human genetics interact and impact upon one another, but there is probably no individual who can work at the cutting edge of all fields - there is no true human geneticist.

Genetics, by its very nature, often involves the study of abnormality. But abnormality is a matter of definition. Sometimes the population cannot be divided into two discrete groups, but shows continuous variation. Intelligence, as measured by some test, is one such trait. In a population the distribution of intelligence follows a bell-shaped or Gaussian curve of continuous variation. Yet, we divide the population into groups (mentally challenged, normal, genius). Other traits show nearly discontinuous variation, disease or nondisease. But when we look closely even these individuals show some continuity, from severely affected, to mildly affected, to normal. Genetic abnormality therefore should be thought of as a continuum.

Abnormality <---------------------------------------> Normality

No one is fully abnormal; no one is fully normal. Each lies somewhere between the two absolutes. Similarly, diseases cannot be classified as strictly genetic or environmental. The phenotype of "genetic" diseases can sometimes be modified, even to the point of nonexpression, by controlling environmental factors. Similarly, environmental (infectious) diseases may not be expressed because of some genetic predisposition to immunity. Each disease, in each individual, lies somewhere on the continuum between a genetic disease and an environmental disease.

Genetic <--------------------------------------------> Environmental

We will continue to speak of genetic diseases. What we really mean is that the disease has a strong genetic component. The classification "genetic" is just a short hand notation meaning the disease lies very far to the left in the above continuum.

There is a great deal of variability in the human population. It has been estimated that each of us has between 50,000 and 100, 000 loci or genes carried in the 3 billion base pairs of DNA in our chromosomes. Up to 1/3 of these may be polymorphic, that is, the frequency of the most common allele is no greater than 0.99. There may be as many as 10,000 "genetic" disorders in the human population. Human variability is estimated to be greater than any other species. As we should discover as we progress through this course, there are advantages to variability that allows us to adapt and survive changing environments, and there are costs associated with the maintenance of this variability in the human population.


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