Introduction

Abstract

Recent discoveries on the molecular structure and function of eukaryotic genomes are of major evolutionary significance. Although inherited changes or mutations have long been recognized as the ultimate source of evolutionary change, the mechanisms underlying these genetic changes were initially assumed to be rather simplistic random events which provided the raw material but not directionality to evolutionary change. In light of recent discoveries, both of these assumptions are today called into question. For example, we now know that inherited changes are the result of much more than simple enzymatic errors made during the process of DNA replication. Indeed, many inherited changes that have significant phenotypic effects are known to be due to the insertion of viral-like transposable elements that comprise a major fraction of all genomes. We now know that the movement of transposable elements, and hence the rate of transposable element-mediated insertional mutation, is not a constant. Rather transposable element movement is a highly regulated process and in many instances may be induced by environmental and other forms of genomic stress. In short, the molecular processes which have resulted in inherited changes over evolutionary time are a good deal more complex than envisioned even a decade ago and, in large measure, are associated with the movement and insertional consequences of transposable elements.