Oct. 24-26, 2009, Yingjie Overseas Exchange Center, Peking University, Beijing, China中文版

The Nearly Neutral Theory of Molecular Evolution

Tomoko Ohta

National Institute of Genetics, Japan

Abstract

The neutral theory of molecular evolution was put forward by M. Kimura. The theory proposes that evolution of genes is by random genetic drift, not by selection. In this theory, new mutations are classified into deleterious, neutral and advantageous classes. I noticed that the intermediate class of mutations between the selected and the neutral classes must be important and proposed the nearly neutral theory in 1973.　The theory emphasizes the interaction of drift and selection. With rapidly increasing genome data, the applicability of the nearly neutral theory to those new data is expanding. In this report, recent progress on the applicability of the nearly neutral theory is reviewed in relation to the evolution of complex systems.
 
１  Protein Coding Regions
The most important prediction of the nearly neutral theory, i. e.,　rapid evolution of species with small population size than that of large population size, has been verified by comparative studies of synonymous and nonsynonymous substitutions among various species. Also, data of DNA polymorphism of various species show preponderance of slightly deleterious mutations.
2  Gene Regulations
It is now recognized that genetic regulatory systems are robust against mutations. Because of such robust systems, individual mutant substitutions may become nearly neutral, but after substitutions of several mutations, a path may be open to creating novel systems. Extra-transcription activity of human genome also depends upon the robustness, and provides flexibility of the system with nearly neutral variations.

The complex systems at these two levels are thought to differ on how they respond to selection pressure. In particular, evolution of gene regulation is characterized by very rapid changes as compared with protein evolution. This is thought to come from the flexibility of the regulatory systems. Therefore gene regulatory system may readily respond to environmental changes. Drift and selection work together on shifting complex systems, providing opportunity for evolution of novel forms and functions. In these processes of shifting, robustness and epigenetics provides various opportunities for evolution of novel systems. We can visualize these complicated processes　as large grey zones containing weak selection, drift, robust genetic networks and epigenetics.

Tomoko Ohta

National Institute of Genetics, Japan

CV

Born on Sept 7, 1933

Address: 
Laboratory of Population Genetics, National Institute of Genetics, Mishima, Shizuoka-ken, 411-8540 Japan

Degrees: 
Ph. D. from North Carolina State University (1967)
Doctor of Science (D. Sc.) from University of Tokyo (1972)

Career: 
Research Member, National Institute of Genetics (1967-1984)
Head of the First Laboratory, Department of Population Genetics(1977-1984)
Professor, Laboratory of Population Genetics (1984-1997)          
Foreign Honorary Member, American Academy of Arts and Sciences (1984)
Professor Emeritus (1997)
Fellow of AAAS (2000)　        
Foreign Associate, National Academy of Sciences, USA (2002)

Research Subjects:
Interaction of Drift and Selection in Molecular Evolution (The Nearly Neutral Theory of Molecular Evolution).
Evolution of Multigene Families.        

Awards: 
The First Saruhashi Prize (Society for Bright Future of Women Scientists, Tokyo) (1981)
Japan Academy Prize (1985)
Avon Special Prize for Women (1986)
Weldon Memorial Prize (Oxford University) (1986)
Person of Cultural Merit (2002)
SMBE Council Award for Lifetime Scientific Contributions to Evolutionary Biology (2006)