In this paper, We will examine how molecular genetics can be used to test various ethological hypotheses. Genes can also be used in the proximate explanation of a trait in a very straightforward manner. If a study finds that some variant of gene X is associated with a variant of behavior Y, we are casting genes in a proximate, rather than an ultimate, light. Identifying the  genes behind behavior traits is a large-scale endeavor going on in hundreds of labs around the world today. Researchers involved in this area examined the molecular genetic underpinning of traits such as foriging, mate choice, aggression, division of labor,and so on. We examine two case studies at the molecular genetic level: ultraviolet vision and  song acquisition in birds.