He compared in his thesis the genomes of mould and yeast fungi. He also developed computational and laboratory methods for analysing the expression of the genome of Trichoderma reesei fungus.

Mould fungi are used for producing enzymes and other proteins. Enzymes are generally used in industrial food, pulp, textile and energy processes. Characteristics of biomass can be modified with the help of enzymes, e.g. in bleaching of jeans or paper. The Trichoderma reesei mould is especially known for its capability to produce proteins efficiently.

Arvas compared computationally the genomes of mould and yeast fungi. The yeasts have half smaller genomes than moulds and they produce less proteins. The dissertation improves understanding of fungal genomes and the relationships of genomes and external characteristics i.e. phenotypes of fungi. This is important to successfully modify the genomes of fungi in order to enhance their protein productivity.

Arvas developed computational and laboratory methods to study gene expression and tested how these can be applied for Trichoderma reesei.

In addition, he studied gene expression of fungi in conditions relevant for protein production. He noticed novel expression responses that can partly explain the good protein productivity of the fungi Trichoderma reesei.

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Considering the high heritabilities for global brain volumes and particular focal brain densities and thicknesses, the search for genes that are involved in brain growth, aging, and brain structure maintenance is important. Such knowledge can help us understand normal developmental and age-associated changes in individual variation in brain functioning. Moreover, it enhances our knowledge of individual variation in brain functioning and facilitates the interpretation of the morphological changes found in psychiatric disorders such as schizophrenia [van Haren et al., 2007]. Also, it allows future efforts to find particular genes responsible for brain structures to be concentrated in areas that are under considerable genetic influence [Hulshoff Pol et al., 2006].

A genetic approach to find genes involved in brain structure that has been applied in several studies is that of diseases with a clear genetic etiology such as Huntington's disease, Down syndrome, Williams syndrome, and Velocardiofacial syndrome. A review reveals for these diseases besides disease specific brain changes, decreases in total brain, white matter, and hippocampus volumes, irrespective of the genes and/or chromosomes involved. This suggests that many genes are probably involved in the individual variation of these measures [Peper et al., in press].

It is important to investigate which environmental factors have an influence on the expression of genes (as found in DNA-methylation). Additionally, the study of interaction between genes and environmental factors is warranted. Furthermore, the simultaneous effects of multiple genes and possibly the interaction among genes, also needs investigation as the high heritability of a complex quantitative phenotype such as brain volume cannot be explained by a single-gene polymorphism

Conclusion

MRI studies in twins indicate that, given the basic additive genetic model, overall brain volume in adulthood is highly heritable. To test for influences of genetic, common, and unique environmental factors or interactions between genetic and environmental influences. twin studies carried out in large and more homogenous samples, analyzed with advanced quantitative genetic methods are needed. To investigate the stability of genetic and environmental influences onto functional neural networks in human brain longitudinal twin studies in childhood as well as in adulthood are needed since brain volume changes dynamically throughout life. New brain-imaging methods, such as DTI-fiber tracking and resting state functional MRI, allow to study the heritability of neural networks underlying brain functioning. These new methods, in coherence with new genetic approaches, will enable us to further disentangle which genes and environmental factors and interactions therein influence human brain structure throughout life.

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