Crop yield is the most important trait in both crop production and breeding. We never stop looking for genes that can increase yield. However, yield is a quantitative trait, controlled by so many genes and affected a lot of by environments. Therefore, the trait “yield” has very low heritability. There has been a lot QTL for yield, but how to clone yield genes? One fact for trait “yield” is that anything can affect it and usually it is just a pleiotropic effect of other genes, genes for heading date (escaping cold or drought), genes for grain number, genes for disease resistance, root length etc. Therefore, when we want to clone a gene underneath a yield QTL. The first thing is to find the trait it really represents. My advisor Dr. Dubcovsky mentioned one really inspiring way to do that: screen all aspects of traits, root, leaf, morphology etc, of two isogenic lines to find the most straight-forward trait!