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Modern Genetic Analysis Chapter 1. Genetics and the Organism
Experimental Genetics

The study of genes has proved to be a powerful approach to understanding biological systems. Because genes affect virtually every aspect of the structure and function of an organism, being able to identify and determine the function of genes is an important step in charting the various processes that underlie a particular character under investigation. Genetics is an approach to all of biology, not just to heredity. What exactly does the genetic approach involve? Many different methodologies are used to study genes and gene activities, but these can be summarized briefly as follows:

1. Isolation of phenotypic variants. Most often the variants used are mutants. Each mutant potentially represents a genetic component of the system under study.
2. Analysis of progeny of controlled matings ("crosses") between phenotypic variants. This type of analysis, begun by Mendel, identifies genes and their alleles, their chromosomal locations, their inheritance patterns, and their interactions.
3. Biochemical analysis of cellular processes controlled by specific genes. Life is basically a complex set of chemical reactions, so studying the ways in which genes control these reactions is an important way of dissecting this complex chemistry. Alleles causing defective biochemical function are invaluable in this type of analysis.
4. Microscopic analysis. Microscopic study of chromosome structure and movement has long been an integral part of genetic analysis, but new technologies have provided ways of labeling the genes themselves and their products so that their locations can be visualized under the microscope.
5. Analysis of DNA. Several techniques, such as cloning, allow the DNA of an individual gene to be isolated for direct analysis. This allows such secondary applications as transgenesis, gene manipulation, and DNA sequencing.

In any one genetic analysis, all these methodologies can be brought to bear on the biological function under study. The approaches are largely complementary and represent a powerful and incisive arsenal for investigation, of which we will see many examples throughout this book. The way these methodologies have been used to deduce the nature of genes is shown in Genetics in Process 1-2 on the following page.

© 1999 by W. H. Freeman and Company. All rights reserved.