Introduction

Abstract

In evolution of higher organisms, gene duplication has apparently played a very important role. For more complex organization, more genetic information is needed, and gene duplication seems to be the only way to achieve it. Ohno (1970) emphasized this theme from various theoretical and empirical points of view. Among better known protein molecules, there are many examples which have originated by gene duplication; e. g., myoglobin and hemoglobin α as well as β, lysozyme and α-lactalbumin, trypsin and chymotrypsin, immunoglobulin κ, λ and heavy chains etc. All these examples clearly show that gene duplication and subsequent functional differentiation have been a major feature of evolution.