The phenotype of a plant is defined by the complex interactions between its genotype and the environment. By growing different natural variants of Arabidopsis thaliana in the same environment, a significant association between genotype and phenotype can lead to the identification of genes involved in plant growth and development. These studies are named genome-wide association studies (GWAS).
A well-known problem with GWAS is that despite a high heritability, only few genetic factors can be identified. We partly solved this problem by lowering the significance threshold and by studying the intermediate levels between genotype and phenotype, such as carbon and nitrogen metabolism. These solutions led to the identification of numerous candidate genes for growth and development.
Furthermore, we studied the effects of epigenetics that could determine a substantial part of the heritability. Our findings show that epigenetic variation, independent of genetic variation, can cause wide variation in plant growth, development and metabolism. We further show that the epigenetic variation can be induced by the environment, can be passed on from grandparent to grandchild, and appears to enhance fitness of the grandchildren. These findings contradict the firm genetic laws and point strongly to Lamarck’s theory of soft inheritance that states that phenotypic changes acquired during a lifetime can be passed on to future generations. It must be noted though that genetic factors and their interaction with the environment will remain the main determinants of phenotypic variation.