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Modern Genetic Analysis Chapter 16. The Genetic Basis of Development
Introduction

In all higher organisms, life begins with a single cell, the newly fertilized egg. It reaches maturity with thousands, millions, or even trillions of cells combined into a complex organism with many integrated organ systems. The goal of developmental biology is to unravel the fascinating and mysterious processes that achieve the transfiguration of egg into adult. Because we know more about development in these organisms, we will restrict most of our discussion to animal systems.

The different cell types of the body are distinguished by the variety and amounts of the proteins that they expressthe protein profile of each cell (that is, the quantitative and qualitative array of proteins that it contains). The protein profile of a cell in a multicellular organism is the end result of a series of genetic regulatory decisions that determine the "when, where, and how much" of gene expression. Thus, for a particular gene, we are interested in which tissues and at what developmental times the gene is transcribed and how much of the gene product is synthesized. From a geneticist's point of view, all developmental programming that controls an organism's protein profiles is determined by the regulatory information encoded in the DNA. We can look at the genome as a parts list of all the gene products (RNAs and polypeptides) that can be potentially produced and as an instruction manual of when, where, and how much of these products are to be expressed. Thus, one aspect of developmental genetics is to understand how this instruction manual operates to send cells down different developmental pathways, ultimately producing a large constellation of characteristic cell types.

This is not all that we want to understand about developmental genetics and production of cellular diversity, however. We also want to understand how these different cell types are deployed in a coherent and constructive distributionin other words, how they become organized into organs and tissues, and how those organ systems and tissues are organized into an integrated, coherently functioning individual organism.

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