Among the many research directions pursued by Susumu Ohno during his illustrious career, three fundamental molecular evolution problems stand out: (1) evolution and properties of the genetic code, (2) evolution by gene duplication and evolution of protein functions, (3) evolution of sex chromosomes in mammals. In this talk, we expound on our recent and ongoing research in these areas.
First, we report on identifying informative positions, intra-molecule relationships, and inter-molecule differences between tRNA subclasses across the three domains of life. Specifically, we apply Bayesian Network modeling and distribution divergence measures to comprehensively analyze the extant tRNA sequence data. We further speculate on the future directions in genetic code origins and evolution research.
Second, we move from Ohno’s seminal theories on evolution by gene duplication and neofunctionalization to a large-scale study of co-evolution of protein functions and protein connectivity. Using comprehensive genomic data and simulation experiments, we show that the relationship between protein connectivity (“multi-functionality”) and evolutionary variability is a complex, non-linear one.    
Third, we propose a new mathematically rigorous model of transitioning from the autosomes to sex chromosomes in vertebrates --- a model that dovetails with Ohno’s hypotheses on sex chromosome evolution and X chromosome dosage compensation and inactivation.
We conclude by outlining how Ohno’s work and ideas continue to be a guiding framework and a fruitful impetus for cutting-edge modern research in the field of molecular evolution.