Introduction

As medical laboratory technologists (MLTs) working in a blood bank, which types of genetics do we need to know and at what level? Keep in mind that genetics is a subject of significance to all disciplines in medical laboratory science (MLS). Also, although there are many kinds of genetics, there are five categories of particular relevance to MLS:

• mendelian genetics, first described by Gregor Mendel in 1865;

• immunogenetics, especially the areas that deal with the genetics of blood groups, immunoglobulins, and the major histocompatibility complex;

• population genetics, based on the Hardy-Weinberg law;

• molecular genetics, whose applications are being used increasingly to diagnose and to treat inherited diseases and viral infections;

• cytogenetics, a subspecialty that is concerned with the microscopic appearance of chromosomes and their behavior during cell division and how these characteristics relate to a person's genotype and phenotype.

Given this complexity, several kinds of genetics are significant to blood bank MLTs. As a minimum to work as a new graduate in a hospital blood bank or blood transfusion service (BTS), you need to understand a variety of genetic terms and symbols that are used routinely in transfusion medicine (TM); you also need to understand how blood groups in each of the major blood group systems (BGS) are inherited.

To work in non-routine areas of TM, you will require additional skills. For example, to do research such as investigating viral infections in donor blood at the molecular level or mapping blood genes, you will need a sound grasp of the theory and methods of molecular genetics. To make sense of current journal articles on genetics, you also need to be fluent in the lexicon of molecular genetics as these articles often refer to such things as the polymerase chain reaction (PCR) and restriction fragment length polymorphisms (RFLPs). Critical to understanding molecular genetics is a strong foundation in biochemistry. If you become involved in investigating the inheritance of newly discovered blood group genes, you will need an in-depth understanding of population genetics.

Of course, as MLTs working in any discipline you are expected to be able to apply the principles of mendelian genetics to a wide variety of inheritance problems. Moreover, as time passes competence in genetics will gain in significance since this discipline is becoming increasingly important to clinical practice in medicine.

Today "knowing" everything is impossible, especially in a complex and evolving field like genetics. The best approach is to learn basic definitions and concepts so that you are functionally literate. You can build on this foundation later as circumstances dictate. In this module we will concentrate on the inheritance of blood groups, genetic terminology and symbols, and inheritance patterns. Take the time to understand these principles and terms. They are core concepts that you will use again when the various BGS are discussed.

Learning genetics entails applying principles to solve problems and puzzles. For example, suppose that two people who are heterozygous for a gene that causes cystic fibrosis (CF) mate and produce children. What percentage of their offspring will have CF? Which inheritance pattern does CF follow? To take another example, if the daughter of a man with hemophilia A mates with a man who does not have hemophilia A, what percentage of their sons will have hemophilia A? Will their affected sons be homozygous, heterozygous, or hemizygous for the gene that cause hemophilia? You will be able to solve these and similar problems after completing this module.

As you progress through the module and come across various genetic terms, be sure to take time to look them up in the glossary (second item under Resources in the left frame).

Overview

Introduction

Historical Perspective