In this chapter, we discuss the inheritance of simple traits that are influenced by one or a few genes. We trace the history of Mendel’s experiments that led to the discovery of dominant and recessive variants and also gave rise to the idea of independent assortment of alleles. We then review Morgan’s experiments with fruit flies and how they led to the discovery of chromosomal linkage. The chapter also discusses human diseases that follow Mendelian inheritance patterns and how we can identify the underlying genes using linkage studies of affected families. Finally, the chapter concludes with a discussion of the effects of selection on dominant and recessive alleles.